lua

lstrlib.c (57546B)

---

 /*
 ** $Id: lstrlib.c $
 ** Standard library for string operations and pattern-matching
 ** See Copyright Notice in lua.h
 */
 
 #define lstrlib_c
 #define LUA_LIB
 
 #include "lprefix.h"
 
 
 #include <ctype.h>
 #include <float.h>
 #include <limits.h>
 #include <locale.h>
 #include <math.h>
 #include <stddef.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 
 #include "lua.h"
 
 #include "lauxlib.h"
 #include "lualib.h"
 #include "llimits.h"
 
 
 /*
 ** maximum number of captures that a pattern can do during
 ** pattern-matching. This limit is arbitrary, but must fit in
 ** an unsigned char.
 */
 #if !defined(LUA_MAXCAPTURES)
 #define LUA_MAXCAPTURES		32
 #endif
 
 
 static int str_len (lua_State *L) {
   size_t l;
   luaL_checklstring(L, 1, &l);
   lua_pushinteger(L, (lua_Integer)l);
   return 1;
 }
 
 
 /*
 ** translate a relative initial string position
 ** (negative means back from end): clip result to [1, inf).
 ** The length of any string in Lua must fit in a lua_Integer,
 ** so there are no overflows in the casts.
 ** The inverted comparison avoids a possible overflow
 ** computing '-pos'.
 */
 static size_t posrelatI (lua_Integer pos, size_t len) {
   if (pos > 0)
     return (size_t)pos;
   else if (pos == 0)
     return 1;
   else if (pos < -(lua_Integer)len)  /* inverted comparison */
     return 1;  /* clip to 1 */
   else return len + (size_t)pos + 1;
 }
 
 
 /*
 ** Gets an optional ending string position from argument 'arg',
 ** with default value 'def'.
 ** Negative means back from end: clip result to [0, len]
 */
 static size_t getendpos (lua_State *L, int arg, lua_Integer def,
                          size_t len) {
   lua_Integer pos = luaL_optinteger(L, arg, def);
   if (pos > (lua_Integer)len)
     return len;
   else if (pos >= 0)
     return (size_t)pos;
   else if (pos < -(lua_Integer)len)
     return 0;
   else return len + (size_t)pos + 1;
 }
 
 
 static int str_sub (lua_State *L) {
   size_t l;
   const char *s = luaL_checklstring(L, 1, &l);
   size_t start = posrelatI(luaL_checkinteger(L, 2), l);
   size_t end = getendpos(L, 3, -1, l);
   if (start <= end)
     lua_pushlstring(L, s + start - 1, (end - start) + 1);
   else lua_pushliteral(L, "");
   return 1;
 }
 
 
 static int str_reverse (lua_State *L) {
   size_t l, i;
   luaL_Buffer b;
   const char *s = luaL_checklstring(L, 1, &l);
   char *p = luaL_buffinitsize(L, &b, l);
   for (i = 0; i < l; i++)
     p[i] = s[l - i - 1];
   luaL_pushresultsize(&b, l);
   return 1;
 }
 
 
 static int str_lower (lua_State *L) {
   size_t l;
   size_t i;
   luaL_Buffer b;
   const char *s = luaL_checklstring(L, 1, &l);
   char *p = luaL_buffinitsize(L, &b, l);
   for (i=0; i<l; i++)
     p[i] = cast_char(tolower(cast_uchar(s[i])));
   luaL_pushresultsize(&b, l);
   return 1;
 }
 
 
 static int str_upper (lua_State *L) {
   size_t l;
   size_t i;
   luaL_Buffer b;
   const char *s = luaL_checklstring(L, 1, &l);
   char *p = luaL_buffinitsize(L, &b, l);
   for (i=0; i<l; i++)
     p[i] = cast_char(toupper(cast_uchar(s[i])));
   luaL_pushresultsize(&b, l);
   return 1;
 }
 
 
 static int str_rep (lua_State *L) {
   size_t l, lsep;
   const char *s = luaL_checklstring(L, 1, &l);
   lua_Integer n = luaL_checkinteger(L, 2);
   const char *sep = luaL_optlstring(L, 3, "", &lsep);
   if (n <= 0)
     lua_pushliteral(L, "");
   else if (l_unlikely(l + lsep < l || l + lsep > MAX_SIZE / cast_sizet(n)))
     return luaL_error(L, "resulting string too large");
   else {
     size_t totallen = ((size_t)n * (l + lsep)) - lsep;
     luaL_Buffer b;
     char *p = luaL_buffinitsize(L, &b, totallen);
     while (n-- > 1) {  /* first n-1 copies (followed by separator) */
       memcpy(p, s, l * sizeof(char)); p += l;
       if (lsep > 0) {  /* empty 'memcpy' is not that cheap */
         memcpy(p, sep, lsep * sizeof(char));
         p += lsep;
       }
     }
     memcpy(p, s, l * sizeof(char));  /* last copy (not followed by separator) */
     luaL_pushresultsize(&b, totallen);
   }
   return 1;
 }
 
 
 static int str_byte (lua_State *L) {
   size_t l;
   const char *s = luaL_checklstring(L, 1, &l);
   lua_Integer pi = luaL_optinteger(L, 2, 1);
   size_t posi = posrelatI(pi, l);
   size_t pose = getendpos(L, 3, pi, l);
   int n, i;
   if (posi > pose) return 0;  /* empty interval; return no values */
   if (l_unlikely(pose - posi >= (size_t)INT_MAX))  /* arithmetic overflow? */
     return luaL_error(L, "string slice too long");
   n = (int)(pose -  posi) + 1;
   luaL_checkstack(L, n, "string slice too long");
   for (i=0; i<n; i++)
     lua_pushinteger(L, cast_uchar(s[posi + cast_uint(i) - 1]));
   return n;
 }
 
 
 static int str_char (lua_State *L) {
   int n = lua_gettop(L);  /* number of arguments */
   int i;
   luaL_Buffer b;
   char *p = luaL_buffinitsize(L, &b, cast_uint(n));
   for (i=1; i<=n; i++) {
     lua_Unsigned c = (lua_Unsigned)luaL_checkinteger(L, i);
     luaL_argcheck(L, c <= (lua_Unsigned)UCHAR_MAX, i, "value out of range");
     p[i - 1] = cast_char(cast_uchar(c));
   }
   luaL_pushresultsize(&b, cast_uint(n));
   return 1;
 }
 
 
 /*
 ** Buffer to store the result of 'string.dump'. It must be initialized
 ** after the call to 'lua_dump', to ensure that the function is on the
 ** top of the stack when 'lua_dump' is called. ('luaL_buffinit' might
 ** push stuff.)
 */
 struct str_Writer {
   int init;  /* true iff buffer has been initialized */
   luaL_Buffer B;
 };
 
 
 static int writer (lua_State *L, const void *b, size_t size, void *ud) {
   struct str_Writer *state = (struct str_Writer *)ud;
   if (!state->init) {
     state->init = 1;
     luaL_buffinit(L, &state->B);
   }
   if (b == NULL) {  /* finishing dump? */
     luaL_pushresult(&state->B);  /* push result */
     lua_replace(L, 1);  /* move it to reserved slot */
   }
   else
     luaL_addlstring(&state->B, (const char *)b, size);
   return 0;
 }
 
 
 static int str_dump (lua_State *L) {
   struct str_Writer state;
   int strip = lua_toboolean(L, 2);
   luaL_argcheck(L, lua_type(L, 1) == LUA_TFUNCTION && !lua_iscfunction(L, 1),
                    1, "Lua function expected");
   /* ensure function is on the top of the stack and vacate slot 1 */
   lua_pushvalue(L, 1);
   state.init = 0;
   lua_dump(L, writer, &state, strip);
   lua_settop(L, 1);  /* leave final result on top */
   return 1;
 }
 
 
 
 /*
 ** {======================================================
 ** METAMETHODS
 ** =======================================================
 */
 
 #if defined(LUA_NOCVTS2N)	/* { */
 
 /* no coercion from strings to numbers */
 
 static const luaL_Reg stringmetamethods[] = {
   {"__index", NULL},  /* placeholder */
   {NULL, NULL}
 };
 
 #else		/* }{ */
 
 static int tonum (lua_State *L, int arg) {
   if (lua_type(L, arg) == LUA_TNUMBER) {  /* already a number? */
     lua_pushvalue(L, arg);
     return 1;
   }
   else {  /* check whether it is a numerical string */
     size_t len;
     const char *s = lua_tolstring(L, arg, &len);
     return (s != NULL && lua_stringtonumber(L, s) == len + 1);
   }
 }
 
 
 static void trymt (lua_State *L, const char *mtname) {
   lua_settop(L, 2);  /* back to the original arguments */
   if (l_unlikely(lua_type(L, 2) == LUA_TSTRING ||
                  !luaL_getmetafield(L, 2, mtname)))
     luaL_error(L, "attempt to %s a '%s' with a '%s'", mtname + 2,
                   luaL_typename(L, -2), luaL_typename(L, -1));
   lua_insert(L, -3);  /* put metamethod before arguments */
   lua_call(L, 2, 1);  /* call metamethod */
 }
 
 
 static int arith (lua_State *L, int op, const char *mtname) {
   if (tonum(L, 1) && tonum(L, 2))
     lua_arith(L, op);  /* result will be on the top */
   else
     trymt(L, mtname);
   return 1;
 }
 
 
 static int arith_add (lua_State *L) {
   return arith(L, LUA_OPADD, "__add");
 }
 
 static int arith_sub (lua_State *L) {
   return arith(L, LUA_OPSUB, "__sub");
 }
 
 static int arith_mul (lua_State *L) {
   return arith(L, LUA_OPMUL, "__mul");
 }
 
 static int arith_mod (lua_State *L) {
   return arith(L, LUA_OPMOD, "__mod");
 }
 
 static int arith_pow (lua_State *L) {
   return arith(L, LUA_OPPOW, "__pow");
 }
 
 static int arith_div (lua_State *L) {
   return arith(L, LUA_OPDIV, "__div");
 }
 
 static int arith_idiv (lua_State *L) {
   return arith(L, LUA_OPIDIV, "__idiv");
 }
 
 static int arith_unm (lua_State *L) {
   return arith(L, LUA_OPUNM, "__unm");
 }
 
 
 static const luaL_Reg stringmetamethods[] = {
   {"__add", arith_add},
   {"__sub", arith_sub},
   {"__mul", arith_mul},
   {"__mod", arith_mod},
   {"__pow", arith_pow},
   {"__div", arith_div},
   {"__idiv", arith_idiv},
   {"__unm", arith_unm},
   {"__index", NULL},  /* placeholder */
   {NULL, NULL}
 };
 
 #endif		/* } */
 
 /* }====================================================== */
 
 /*
 ** {======================================================
 ** PATTERN MATCHING
 ** =======================================================
 */
 
 
 #define CAP_UNFINISHED	(-1)
 #define CAP_POSITION	(-2)
 
 
 typedef struct MatchState {
   const char *src_init;  /* init of source string */
   const char *src_end;  /* end ('\0') of source string */
   const char *p_end;  /* end ('\0') of pattern */
   lua_State *L;
   int matchdepth;  /* control for recursive depth (to avoid C stack overflow) */
   int level;  /* total number of captures (finished or unfinished) */
   struct {
     const char *init;
     ptrdiff_t len;  /* length or special value (CAP_*) */
   } capture[LUA_MAXCAPTURES];
 } MatchState;
 
 
 /* recursive function */
 static const char *match (MatchState *ms, const char *s, const char *p);
 
 
 /* maximum recursion depth for 'match' */
 #if !defined(MAXCCALLS)
 #define MAXCCALLS	200
 #endif
 
 
 #define L_ESC		'%'
 #define SPECIALS	"^$*+?.([%-"
 
 
 static int check_capture (MatchState *ms, int l) {
   l -= '1';
   if (l_unlikely(l < 0 || l >= ms->level ||
                  ms->capture[l].len == CAP_UNFINISHED))
     return luaL_error(ms->L, "invalid capture index %%%d", l + 1);
   return l;
 }
 
 
 static int capture_to_close (MatchState *ms) {
   int level = ms->level;
   for (level--; level>=0; level--)
     if (ms->capture[level].len == CAP_UNFINISHED) return level;
   return luaL_error(ms->L, "invalid pattern capture");
 }
 
 
 static const char *classend (MatchState *ms, const char *p) {
   switch (*p++) {
     case L_ESC: {
       if (l_unlikely(p == ms->p_end))
         luaL_error(ms->L, "malformed pattern (ends with '%%')");
       return p+1;
     }
     case '[': {
       if (*p == '^') p++;
       do {  /* look for a ']' */
         if (l_unlikely(p == ms->p_end))
           luaL_error(ms->L, "malformed pattern (missing ']')");
         if (*(p++) == L_ESC && p < ms->p_end)
           p++;  /* skip escapes (e.g. '%]') */
       } while (*p != ']');
       return p+1;
     }
     default: {
       return p;
     }
   }
 }
 
 
 static int match_class (int c, int cl) {
   int res;
   switch (tolower(cl)) {
     case 'a' : res = isalpha(c); break;
     case 'c' : res = iscntrl(c); break;
     case 'd' : res = isdigit(c); break;
     case 'g' : res = isgraph(c); break;
     case 'l' : res = islower(c); break;
     case 'p' : res = ispunct(c); break;
     case 's' : res = isspace(c); break;
     case 'u' : res = isupper(c); break;
     case 'w' : res = isalnum(c); break;
     case 'x' : res = isxdigit(c); break;
     case 'z' : res = (c == 0); break;  /* deprecated option */
     default: return (cl == c);
   }
   return (islower(cl) ? res : !res);
 }
 
 
 static int matchbracketclass (int c, const char *p, const char *ec) {
   int sig = 1;
   if (*(p+1) == '^') {
     sig = 0;
     p++;  /* skip the '^' */
   }
   while (++p < ec) {
     if (*p == L_ESC) {
       p++;
       if (match_class(c, cast_uchar(*p)))
         return sig;
     }
     else if ((*(p+1) == '-') && (p+2 < ec)) {
       p+=2;
       if (cast_uchar(*(p-2)) <= c && c <= cast_uchar(*p))
         return sig;
     }
     else if (cast_uchar(*p) == c) return sig;
   }
   return !sig;
 }
 
 
 static int singlematch (MatchState *ms, const char *s, const char *p,
                         const char *ep) {
   if (s >= ms->src_end)
     return 0;
   else {
     int c = cast_uchar(*s);
     switch (*p) {
       case '.': return 1;  /* matches any char */
       case L_ESC: return match_class(c, cast_uchar(*(p+1)));
       case '[': return matchbracketclass(c, p, ep-1);
       default:  return (cast_uchar(*p) == c);
     }
   }
 }
 
 
 static const char *matchbalance (MatchState *ms, const char *s,
                                    const char *p) {
   if (l_unlikely(p >= ms->p_end - 1))
     luaL_error(ms->L, "malformed pattern (missing arguments to '%%b')");
   if (*s != *p) return NULL;
   else {
     int b = *p;
     int e = *(p+1);
     int cont = 1;
     while (++s < ms->src_end) {
       if (*s == e) {
         if (--cont == 0) return s+1;
       }
       else if (*s == b) cont++;
     }
   }
   return NULL;  /* string ends out of balance */
 }
 
 
 static const char *max_expand (MatchState *ms, const char *s,
                                  const char *p, const char *ep) {
   ptrdiff_t i = 0;  /* counts maximum expand for item */
   while (singlematch(ms, s + i, p, ep))
     i++;
   /* keeps trying to match with the maximum repetitions */
   while (i>=0) {
     const char *res = match(ms, (s+i), ep+1);
     if (res) return res;
     i--;  /* else didn't match; reduce 1 repetition to try again */
   }
   return NULL;
 }
 
 
 static const char *min_expand (MatchState *ms, const char *s,
                                  const char *p, const char *ep) {
   for (;;) {
     const char *res = match(ms, s, ep+1);
     if (res != NULL)
       return res;
     else if (singlematch(ms, s, p, ep))
       s++;  /* try with one more repetition */
     else return NULL;
   }
 }
 
 
 static const char *start_capture (MatchState *ms, const char *s,
                                     const char *p, int what) {
   const char *res;
   int level = ms->level;
   if (level >= LUA_MAXCAPTURES) luaL_error(ms->L, "too many captures");
   ms->capture[level].init = s;
   ms->capture[level].len = what;
   ms->level = level+1;
   if ((res=match(ms, s, p)) == NULL)  /* match failed? */
     ms->level--;  /* undo capture */
   return res;
 }
 
 
 static const char *end_capture (MatchState *ms, const char *s,
                                   const char *p) {
   int l = capture_to_close(ms);
   const char *res;
   ms->capture[l].len = s - ms->capture[l].init;  /* close capture */
   if ((res = match(ms, s, p)) == NULL)  /* match failed? */
     ms->capture[l].len = CAP_UNFINISHED;  /* undo capture */
   return res;
 }
 
 
 static const char *match_capture (MatchState *ms, const char *s, int l) {
   size_t len;
   l = check_capture(ms, l);
   len = cast_sizet(ms->capture[l].len);
   if ((size_t)(ms->src_end-s) >= len &&
       memcmp(ms->capture[l].init, s, len) == 0)
     return s+len;
   else return NULL;
 }
 
 
 static const char *match (MatchState *ms, const char *s, const char *p) {
   if (l_unlikely(ms->matchdepth-- == 0))
     luaL_error(ms->L, "pattern too complex");
   init: /* using goto to optimize tail recursion */
   if (p != ms->p_end) {  /* end of pattern? */
     switch (*p) {
       case '(': {  /* start capture */
         if (*(p + 1) == ')')  /* position capture? */
           s = start_capture(ms, s, p + 2, CAP_POSITION);
         else
           s = start_capture(ms, s, p + 1, CAP_UNFINISHED);
         break;
       }
       case ')': {  /* end capture */
         s = end_capture(ms, s, p + 1);
         break;
       }
       case '$': {
         if ((p + 1) != ms->p_end)  /* is the '$' the last char in pattern? */
           goto dflt;  /* no; go to default */
         s = (s == ms->src_end) ? s : NULL;  /* check end of string */
         break;
       }
       case L_ESC: {  /* escaped sequences not in the format class[*+?-]? */
         switch (*(p + 1)) {
           case 'b': {  /* balanced string? */
             s = matchbalance(ms, s, p + 2);
             if (s != NULL) {
               p += 4; goto init;  /* return match(ms, s, p + 4); */
             }  /* else fail (s == NULL) */
             break;
           }
           case 'f': {  /* frontier? */
             const char *ep; char previous;
             p += 2;
             if (l_unlikely(*p != '['))
               luaL_error(ms->L, "missing '[' after '%%f' in pattern");
             ep = classend(ms, p);  /* points to what is next */
             previous = (s == ms->src_init) ? '\0' : *(s - 1);
             if (!matchbracketclass(cast_uchar(previous), p, ep - 1) &&
                matchbracketclass(cast_uchar(*s), p, ep - 1)) {
               p = ep; goto init;  /* return match(ms, s, ep); */
             }
             s = NULL;  /* match failed */
             break;
           }
           case '0': case '1': case '2': case '3':
           case '4': case '5': case '6': case '7':
           case '8': case '9': {  /* capture results (%0-%9)? */
             s = match_capture(ms, s, cast_uchar(*(p + 1)));
             if (s != NULL) {
               p += 2; goto init;  /* return match(ms, s, p + 2) */
             }
             break;
           }
           default: goto dflt;
         }
         break;
       }
       default: dflt: {  /* pattern class plus optional suffix */
         const char *ep = classend(ms, p);  /* points to optional suffix */
         /* does not match at least once? */
         if (!singlematch(ms, s, p, ep)) {
           if (*ep == '*' || *ep == '?' || *ep == '-') {  /* accept empty? */
             p = ep + 1; goto init;  /* return match(ms, s, ep + 1); */
           }
           else  /* '+' or no suffix */
             s = NULL;  /* fail */
         }
         else {  /* matched once */
           switch (*ep) {  /* handle optional suffix */
             case '?': {  /* optional */
               const char *res;
               if ((res = match(ms, s + 1, ep + 1)) != NULL)
                 s = res;
               else {
                 p = ep + 1; goto init;  /* else return match(ms, s, ep + 1); */
               }
               break;
             }
             case '+':  /* 1 or more repetitions */
               s++;  /* 1 match already done */
               /* FALLTHROUGH */
             case '*':  /* 0 or more repetitions */
               s = max_expand(ms, s, p, ep);
               break;
             case '-':  /* 0 or more repetitions (minimum) */
               s = min_expand(ms, s, p, ep);
               break;
             default:  /* no suffix */
               s++; p = ep; goto init;  /* return match(ms, s + 1, ep); */
           }
         }
         break;
       }
     }
   }
   ms->matchdepth++;
   return s;
 }
 
 
 
 static const char *lmemfind (const char *s1, size_t l1,
                                const char *s2, size_t l2) {
   if (l2 == 0) return s1;  /* empty strings are everywhere */
   else if (l2 > l1) return NULL;  /* avoids a negative 'l1' */
   else {
     const char *init;  /* to search for a '*s2' inside 's1' */
     l2--;  /* 1st char will be checked by 'memchr' */
     l1 = l1-l2;  /* 's2' cannot be found after that */
     while (l1 > 0 && (init = (const char *)memchr(s1, *s2, l1)) != NULL) {
       init++;   /* 1st char is already checked */
       if (memcmp(init, s2+1, l2) == 0)
         return init-1;
       else {  /* correct 'l1' and 's1' to try again */
         l1 -= ct_diff2sz(init - s1);
         s1 = init;
       }
     }
     return NULL;  /* not found */
   }
 }
 
 
 /*
 ** get information about the i-th capture. If there are no captures
 ** and 'i==0', return information about the whole match, which
 ** is the range 's'..'e'. If the capture is a string, return
 ** its length and put its address in '*cap'. If it is an integer
 ** (a position), push it on the stack and return CAP_POSITION.
 */
 static ptrdiff_t get_onecapture (MatchState *ms, int i, const char *s,
                               const char *e, const char **cap) {
   if (i >= ms->level) {
     if (l_unlikely(i != 0))
       luaL_error(ms->L, "invalid capture index %%%d", i + 1);
     *cap = s;
     return (e - s);
   }
   else {
     ptrdiff_t capl = ms->capture[i].len;
     *cap = ms->capture[i].init;
     if (l_unlikely(capl == CAP_UNFINISHED))
       luaL_error(ms->L, "unfinished capture");
     else if (capl == CAP_POSITION)
       lua_pushinteger(ms->L,
           ct_diff2S(ms->capture[i].init - ms->src_init) + 1);
     return capl;
   }
 }
 
 
 /*
 ** Push the i-th capture on the stack.
 */
 static void push_onecapture (MatchState *ms, int i, const char *s,
                                                     const char *e) {
   const char *cap;
   ptrdiff_t l = get_onecapture(ms, i, s, e, &cap);
   if (l != CAP_POSITION)
     lua_pushlstring(ms->L, cap, cast_sizet(l));
   /* else position was already pushed */
 }
 
 
 static int push_captures (MatchState *ms, const char *s, const char *e) {
   int i;
   int nlevels = (ms->level == 0 && s) ? 1 : ms->level;
   luaL_checkstack(ms->L, nlevels, "too many captures");
   for (i = 0; i < nlevels; i++)
     push_onecapture(ms, i, s, e);
   return nlevels;  /* number of strings pushed */
 }
 
 
 /* check whether pattern has no special characters */
 static int nospecials (const char *p, size_t l) {
   size_t upto = 0;
   do {
     if (strpbrk(p + upto, SPECIALS))
       return 0;  /* pattern has a special character */
     upto += strlen(p + upto) + 1;  /* may have more after \0 */
   } while (upto <= l);
   return 1;  /* no special chars found */
 }
 
 
 static void prepstate (MatchState *ms, lua_State *L,
                        const char *s, size_t ls, const char *p, size_t lp) {
   ms->L = L;
   ms->matchdepth = MAXCCALLS;
   ms->src_init = s;
   ms->src_end = s + ls;
   ms->p_end = p + lp;
 }
 
 
 static void reprepstate (MatchState *ms) {
   ms->level = 0;
   lua_assert(ms->matchdepth == MAXCCALLS);
 }
 
 
 static int str_find_aux (lua_State *L, int find) {
   size_t ls, lp;
   const char *s = luaL_checklstring(L, 1, &ls);
   const char *p = luaL_checklstring(L, 2, &lp);
   size_t init = posrelatI(luaL_optinteger(L, 3, 1), ls) - 1;
   if (init > ls) {  /* start after string's end? */
     luaL_pushfail(L);  /* cannot find anything */
     return 1;
   }
   /* explicit request or no special characters? */
   if (find && (lua_toboolean(L, 4) || nospecials(p, lp))) {
     /* do a plain search */
     const char *s2 = lmemfind(s + init, ls - init, p, lp);
     if (s2) {
       lua_pushinteger(L, ct_diff2S(s2 - s) + 1);
       lua_pushinteger(L, cast_st2S(ct_diff2sz(s2 - s) + lp));
       return 2;
     }
   }
   else {
     MatchState ms;
     const char *s1 = s + init;
     int anchor = (*p == '^');
     if (anchor) {
       p++; lp--;  /* skip anchor character */
     }
     prepstate(&ms, L, s, ls, p, lp);
     do {
       const char *res;
       reprepstate(&ms);
       if ((res=match(&ms, s1, p)) != NULL) {
         if (find) {
           lua_pushinteger(L, ct_diff2S(s1 - s) + 1);  /* start */
           lua_pushinteger(L, ct_diff2S(res - s));   /* end */
           return push_captures(&ms, NULL, 0) + 2;
         }
         else
           return push_captures(&ms, s1, res);
       }
     } while (s1++ < ms.src_end && !anchor);
   }
   luaL_pushfail(L);  /* not found */
   return 1;
 }
 
 
 static int str_find (lua_State *L) {
   return str_find_aux(L, 1);
 }
 
 
 static int str_match (lua_State *L) {
   return str_find_aux(L, 0);
 }
 
 
 /* state for 'gmatch' */
 typedef struct GMatchState {
   const char *src;  /* current position */
   const char *p;  /* pattern */
   const char *lastmatch;  /* end of last match */
   MatchState ms;  /* match state */
 } GMatchState;
 
 
 static int gmatch_aux (lua_State *L) {
   GMatchState *gm = (GMatchState *)lua_touserdata(L, lua_upvalueindex(3));
   const char *src;
   gm->ms.L = L;
   for (src = gm->src; src <= gm->ms.src_end; src++) {
     const char *e;
     reprepstate(&gm->ms);
     if ((e = match(&gm->ms, src, gm->p)) != NULL && e != gm->lastmatch) {
       gm->src = gm->lastmatch = e;
       return push_captures(&gm->ms, src, e);
     }
   }
   return 0;  /* not found */
 }
 
 
 static int gmatch (lua_State *L) {
   size_t ls, lp;
   const char *s = luaL_checklstring(L, 1, &ls);
   const char *p = luaL_checklstring(L, 2, &lp);
   size_t init = posrelatI(luaL_optinteger(L, 3, 1), ls) - 1;
   GMatchState *gm;
   lua_settop(L, 2);  /* keep strings on closure to avoid being collected */
   gm = (GMatchState *)lua_newuserdatauv(L, sizeof(GMatchState), 0);
   if (init > ls)  /* start after string's end? */
     init = ls + 1;  /* avoid overflows in 's + init' */
   prepstate(&gm->ms, L, s, ls, p, lp);
   gm->src = s + init; gm->p = p; gm->lastmatch = NULL;
   lua_pushcclosure(L, gmatch_aux, 3);
   return 1;
 }
 
 
 static void add_s (MatchState *ms, luaL_Buffer *b, const char *s,
                                                    const char *e) {
   size_t l;
   lua_State *L = ms->L;
   const char *news = lua_tolstring(L, 3, &l);
   const char *p;
   while ((p = (char *)memchr(news, L_ESC, l)) != NULL) {
     luaL_addlstring(b, news, ct_diff2sz(p - news));
     p++;  /* skip ESC */
     if (*p == L_ESC)  /* '%%' */
       luaL_addchar(b, *p);
     else if (*p == '0')  /* '%0' */
         luaL_addlstring(b, s, ct_diff2sz(e - s));
     else if (isdigit(cast_uchar(*p))) {  /* '%n' */
       const char *cap;
       ptrdiff_t resl = get_onecapture(ms, *p - '1', s, e, &cap);
       if (resl == CAP_POSITION)
         luaL_addvalue(b);  /* add position to accumulated result */
       else
         luaL_addlstring(b, cap, cast_sizet(resl));
     }
     else
       luaL_error(L, "invalid use of '%c' in replacement string", L_ESC);
     l -= ct_diff2sz(p + 1 - news);
     news = p + 1;
   }
   luaL_addlstring(b, news, l);
 }
 
 
 /*
 ** Add the replacement value to the string buffer 'b'.
 ** Return true if the original string was changed. (Function calls and
 ** table indexing resulting in nil or false do not change the subject.)
 */
 static int add_value (MatchState *ms, luaL_Buffer *b, const char *s,
                                       const char *e, int tr) {
   lua_State *L = ms->L;
   switch (tr) {
     case LUA_TFUNCTION: {  /* call the function */
       int n;
       lua_pushvalue(L, 3);  /* push the function */
       n = push_captures(ms, s, e);  /* all captures as arguments */
       lua_call(L, n, 1);  /* call it */
       break;
     }
     case LUA_TTABLE: {  /* index the table */
       push_onecapture(ms, 0, s, e);  /* first capture is the index */
       lua_gettable(L, 3);
       break;
     }
     default: {  /* LUA_TNUMBER or LUA_TSTRING */
       add_s(ms, b, s, e);  /* add value to the buffer */
       return 1;  /* something changed */
     }
   }
   if (!lua_toboolean(L, -1)) {  /* nil or false? */
     lua_pop(L, 1);  /* remove value */
     luaL_addlstring(b, s, ct_diff2sz(e - s));  /* keep original text */
     return 0;  /* no changes */
   }
   else if (l_unlikely(!lua_isstring(L, -1)))
     return luaL_error(L, "invalid replacement value (a %s)",
                          luaL_typename(L, -1));
   else {
     luaL_addvalue(b);  /* add result to accumulator */
     return 1;  /* something changed */
   }
 }
 
 
 static int str_gsub (lua_State *L) {
   size_t srcl, lp;
   const char *src = luaL_checklstring(L, 1, &srcl);  /* subject */
   const char *p = luaL_checklstring(L, 2, &lp);  /* pattern */
   const char *lastmatch = NULL;  /* end of last match */
   int tr = lua_type(L, 3);  /* replacement type */
   /* max replacements */
   lua_Integer max_s = luaL_optinteger(L, 4, cast_st2S(srcl) + 1);
   int anchor = (*p == '^');
   lua_Integer n = 0;  /* replacement count */
   int changed = 0;  /* change flag */
   MatchState ms;
   luaL_Buffer b;
   luaL_argexpected(L, tr == LUA_TNUMBER || tr == LUA_TSTRING ||
                    tr == LUA_TFUNCTION || tr == LUA_TTABLE, 3,
                       "string/function/table");
   luaL_buffinit(L, &b);
   if (anchor) {
     p++; lp--;  /* skip anchor character */
   }
   prepstate(&ms, L, src, srcl, p, lp);
   while (n < max_s) {
     const char *e;
     reprepstate(&ms);  /* (re)prepare state for new match */
     if ((e = match(&ms, src, p)) != NULL && e != lastmatch) {  /* match? */
       n++;
       changed = add_value(&ms, &b, src, e, tr) | changed;
       src = lastmatch = e;
     }
     else if (src < ms.src_end)  /* otherwise, skip one character */
       luaL_addchar(&b, *src++);
     else break;  /* end of subject */
     if (anchor) break;
   }
   if (!changed)  /* no changes? */
     lua_pushvalue(L, 1);  /* return original string */
   else {  /* something changed */
     luaL_addlstring(&b, src, ct_diff2sz(ms.src_end - src));
     luaL_pushresult(&b);  /* create and return new string */
   }
   lua_pushinteger(L, n);  /* number of substitutions */
   return 2;
 }
 
 /* }====================================================== */
 
 
 
 /*
 ** {======================================================
 ** STRING FORMAT
 ** =======================================================
 */
 
 #if !defined(lua_number2strx)	/* { */
 
 /*
 ** Hexadecimal floating-point formatter
 */
 
 #define SIZELENMOD	(sizeof(LUA_NUMBER_FRMLEN)/sizeof(char))
 
 
 /*
 ** Number of bits that goes into the first digit. It can be any value
 ** between 1 and 4; the following definition tries to align the number
 ** to nibble boundaries by making what is left after that first digit a
 ** multiple of 4.
 */
 #define L_NBFD		((l_floatatt(MANT_DIG) - 1)%4 + 1)
 
 
 /*
 ** Add integer part of 'x' to buffer and return new 'x'
 */
 static lua_Number adddigit (char *buff, unsigned n, lua_Number x) {
   lua_Number dd = l_mathop(floor)(x);  /* get integer part from 'x' */
   int d = (int)dd;
   buff[n] = cast_char(d < 10 ? d + '0' : d - 10 + 'a');  /* add to buffer */
   return x - dd;  /* return what is left */
 }
 
 
 static int num2straux (char *buff, unsigned sz, lua_Number x) {
   /* if 'inf' or 'NaN', format it like '%g' */
   if (x != x || x == (lua_Number)HUGE_VAL || x == -(lua_Number)HUGE_VAL)
     return l_sprintf(buff, sz, LUA_NUMBER_FMT, (LUAI_UACNUMBER)x);
   else if (x == 0) {  /* can be -0... */
     /* create "0" or "-0" followed by exponent */
     return l_sprintf(buff, sz, LUA_NUMBER_FMT "x0p+0", (LUAI_UACNUMBER)x);
   }
   else {
     int e;
     lua_Number m = l_mathop(frexp)(x, &e);  /* 'x' fraction and exponent */
     unsigned n = 0;  /* character count */
     if (m < 0) {  /* is number negative? */
       buff[n++] = '-';  /* add sign */
       m = -m;  /* make it positive */
     }
     buff[n++] = '0'; buff[n++] = 'x';  /* add "0x" */
     m = adddigit(buff, n++, m * (1 << L_NBFD));  /* add first digit */
     e -= L_NBFD;  /* this digit goes before the radix point */
     if (m > 0) {  /* more digits? */
       buff[n++] = lua_getlocaledecpoint();  /* add radix point */
       do {  /* add as many digits as needed */
         m = adddigit(buff, n++, m * 16);
       } while (m > 0);
     }
     n += cast_uint(l_sprintf(buff + n, sz - n, "p%+d", e));  /* add exponent */
     lua_assert(n < sz);
     return cast_int(n);
   }
 }
 
 
 static int lua_number2strx (lua_State *L, char *buff, unsigned sz,
                             const char *fmt, lua_Number x) {
   int n = num2straux(buff, sz, x);
   if (fmt[SIZELENMOD] == 'A') {
     int i;
     for (i = 0; i < n; i++)
       buff[i] = cast_char(toupper(cast_uchar(buff[i])));
   }
   else if (l_unlikely(fmt[SIZELENMOD] != 'a'))
     return luaL_error(L, "modifiers for format '%%a'/'%%A' not implemented");
   return n;
 }
 
 #endif				/* } */
 
 
 /*
 ** Maximum size for items formatted with '%f'. This size is produced
 ** by format('%.99f', -maxfloat), and is equal to 99 + 3 ('-', '.',
 ** and '\0') + number of decimal digits to represent maxfloat (which
 ** is maximum exponent + 1). (99+3+1, adding some extra, 110)
 */
 #define MAX_ITEMF	(110 + l_floatatt(MAX_10_EXP))
 
 
 /*
 ** All formats except '%f' do not need that large limit.  The other
 ** float formats use exponents, so that they fit in the 99 limit for
 ** significant digits; 's' for large strings and 'q' add items directly
 ** to the buffer; all integer formats also fit in the 99 limit.  The
 ** worst case are floats: they may need 99 significant digits, plus
 ** '0x', '-', '.', 'e+XXXX', and '\0'. Adding some extra, 120.
 */
 #define MAX_ITEM	120
 
 
 /* valid flags in a format specification */
 #if !defined(L_FMTFLAGSF)
 
 /* valid flags for a, A, e, E, f, F, g, and G conversions */
 #define L_FMTFLAGSF	"-+#0 "
 
 /* valid flags for o, x, and X conversions */
 #define L_FMTFLAGSX	"-#0"
 
 /* valid flags for d and i conversions */
 #define L_FMTFLAGSI	"-+0 "
 
 /* valid flags for u conversions */
 #define L_FMTFLAGSU	"-0"
 
 /* valid flags for c, p, and s conversions */
 #define L_FMTFLAGSC	"-"
 
 #endif
 
 
 /*
 ** Maximum size of each format specification (such as "%-099.99d"):
 ** Initial '%', flags (up to 5), width (2), period, precision (2),
 ** length modifier (8), conversion specifier, and final '\0', plus some
 ** extra.
 */
 #define MAX_FORMAT	32
 
 
 static void addquoted (luaL_Buffer *b, const char *s, size_t len) {
   luaL_addchar(b, '"');
   while (len--) {
     if (*s == '"' || *s == '\\' || *s == '\n') {
       luaL_addchar(b, '\\');
       luaL_addchar(b, *s);
     }
     else if (iscntrl(cast_uchar(*s))) {
       char buff[10];
       if (!isdigit(cast_uchar(*(s+1))))
         l_sprintf(buff, sizeof(buff), "\\%d", (int)cast_uchar(*s));
       else
         l_sprintf(buff, sizeof(buff), "\\%03d", (int)cast_uchar(*s));
       luaL_addstring(b, buff);
     }
     else
       luaL_addchar(b, *s);
     s++;
   }
   luaL_addchar(b, '"');
 }
 
 
 /*
 ** Serialize a floating-point number in such a way that it can be
 ** scanned back by Lua. Use hexadecimal format for "common" numbers
 ** (to preserve precision); inf, -inf, and NaN are handled separately.
 ** (NaN cannot be expressed as a numeral, so we write '(0/0)' for it.)
 */
 static int quotefloat (lua_State *L, char *buff, lua_Number n) {
   const char *s;  /* for the fixed representations */
   if (n == (lua_Number)HUGE_VAL)  /* inf? */
     s = "1e9999";
   else if (n == -(lua_Number)HUGE_VAL)  /* -inf? */
     s = "-1e9999";
   else if (n != n)  /* NaN? */
     s = "(0/0)";
   else {  /* format number as hexadecimal */
     int  nb = lua_number2strx(L, buff, MAX_ITEM,
                                  "%" LUA_NUMBER_FRMLEN "a", n);
     /* ensures that 'buff' string uses a dot as the radix character */
     if (memchr(buff, '.', cast_uint(nb)) == NULL) {  /* no dot? */
       char point = lua_getlocaledecpoint();  /* try locale point */
       char *ppoint = (char *)memchr(buff, point, cast_uint(nb));
       if (ppoint) *ppoint = '.';  /* change it to a dot */
     }
     return nb;
   }
   /* for the fixed representations */
   return l_sprintf(buff, MAX_ITEM, "%s", s);
 }
 
 
 static void addliteral (lua_State *L, luaL_Buffer *b, int arg) {
   switch (lua_type(L, arg)) {
     case LUA_TSTRING: {
       size_t len;
       const char *s = lua_tolstring(L, arg, &len);
       addquoted(b, s, len);
       break;
     }
     case LUA_TNUMBER: {
       char *buff = luaL_prepbuffsize(b, MAX_ITEM);
       int nb;
       if (!lua_isinteger(L, arg))  /* float? */
         nb = quotefloat(L, buff, lua_tonumber(L, arg));
       else {  /* integers */
         lua_Integer n = lua_tointeger(L, arg);
         const char *format = (n == LUA_MININTEGER)  /* corner case? */
                            ? "0x%" LUA_INTEGER_FRMLEN "x"  /* use hex */
                            : LUA_INTEGER_FMT;  /* else use default format */
         nb = l_sprintf(buff, MAX_ITEM, format, (LUAI_UACINT)n);
       }
       luaL_addsize(b, cast_uint(nb));
       break;
     }
     case LUA_TNIL: case LUA_TBOOLEAN: {
       luaL_tolstring(L, arg, NULL);
       luaL_addvalue(b);
       break;
     }
     default: {
       luaL_argerror(L, arg, "value has no literal form");
     }
   }
 }
 
 
 static const char *get2digits (const char *s) {
   if (isdigit(cast_uchar(*s))) {
     s++;
     if (isdigit(cast_uchar(*s))) s++;  /* (2 digits at most) */
   }
   return s;
 }
 
 
 /*
 ** Check whether a conversion specification is valid. When called,
 ** first character in 'form' must be '%' and last character must
 ** be a valid conversion specifier. 'flags' are the accepted flags;
 ** 'precision' signals whether to accept a precision.
 */
 static void checkformat (lua_State *L, const char *form, const char *flags,
                                        int precision) {
   const char *spec = form + 1;  /* skip '%' */
   spec += strspn(spec, flags);  /* skip flags */
   if (*spec != '0') {  /* a width cannot start with '0' */
     spec = get2digits(spec);  /* skip width */
     if (*spec == '.' && precision) {
       spec++;
       spec = get2digits(spec);  /* skip precision */
     }
   }
   if (!isalpha(cast_uchar(*spec)))  /* did not go to the end? */
     luaL_error(L, "invalid conversion specification: '%s'", form);
 }
 
 
 /*
 ** Get a conversion specification and copy it to 'form'.
 ** Return the address of its last character.
 */
 static const char *getformat (lua_State *L, const char *strfrmt,
                                             char *form) {
   /* spans flags, width, and precision ('0' is included as a flag) */
   size_t len = strspn(strfrmt, L_FMTFLAGSF "123456789.");
   len++;  /* adds following character (should be the specifier) */
   /* still needs space for '%', '\0', plus a length modifier */
   if (len >= MAX_FORMAT - 10)
     luaL_error(L, "invalid format (too long)");
   *(form++) = '%';
   memcpy(form, strfrmt, len * sizeof(char));
   *(form + len) = '\0';
   return strfrmt + len - 1;
 }
 
 
 /*
 ** add length modifier into formats
 */
 static void addlenmod (char *form, const char *lenmod) {
   size_t l = strlen(form);
   size_t lm = strlen(lenmod);
   char spec = form[l - 1];
   strcpy(form + l - 1, lenmod);
   form[l + lm - 1] = spec;
   form[l + lm] = '\0';
 }
 
 
 static int str_format (lua_State *L) {
   int top = lua_gettop(L);
   int arg = 1;
   size_t sfl;
   const char *strfrmt = luaL_checklstring(L, arg, &sfl);
   const char *strfrmt_end = strfrmt+sfl;
   const char *flags;
   luaL_Buffer b;
   luaL_buffinit(L, &b);
   while (strfrmt < strfrmt_end) {
     if (*strfrmt != L_ESC)
       luaL_addchar(&b, *strfrmt++);
     else if (*++strfrmt == L_ESC)
       luaL_addchar(&b, *strfrmt++);  /* %% */
     else { /* format item */
       char form[MAX_FORMAT];  /* to store the format ('%...') */
       unsigned maxitem = MAX_ITEM;  /* maximum length for the result */
       char *buff = luaL_prepbuffsize(&b, maxitem);  /* to put result */
       int nb = 0;  /* number of bytes in result */
       if (++arg > top)
         return luaL_argerror(L, arg, "no value");
       strfrmt = getformat(L, strfrmt, form);
       switch (*strfrmt++) {
         case 'c': {
           checkformat(L, form, L_FMTFLAGSC, 0);
           nb = l_sprintf(buff, maxitem, form, (int)luaL_checkinteger(L, arg));
           break;
         }
         case 'd': case 'i':
           flags = L_FMTFLAGSI;
           goto intcase;
         case 'u':
           flags = L_FMTFLAGSU;
           goto intcase;
         case 'o': case 'x': case 'X':
           flags = L_FMTFLAGSX;
          intcase: {
           lua_Integer n = luaL_checkinteger(L, arg);
           checkformat(L, form, flags, 1);
           addlenmod(form, LUA_INTEGER_FRMLEN);
           nb = l_sprintf(buff, maxitem, form, (LUAI_UACINT)n);
           break;
         }
         case 'a': case 'A':
           checkformat(L, form, L_FMTFLAGSF, 1);
           addlenmod(form, LUA_NUMBER_FRMLEN);
           nb = lua_number2strx(L, buff, maxitem, form,
                                   luaL_checknumber(L, arg));
           break;
         case 'f':
           maxitem = MAX_ITEMF;  /* extra space for '%f' */
           buff = luaL_prepbuffsize(&b, maxitem);
           /* FALLTHROUGH */
         case 'e': case 'E': case 'g': case 'G': {
           lua_Number n = luaL_checknumber(L, arg);
           checkformat(L, form, L_FMTFLAGSF, 1);
           addlenmod(form, LUA_NUMBER_FRMLEN);
           nb = l_sprintf(buff, maxitem, form, (LUAI_UACNUMBER)n);
           break;
         }
         case 'p': {
           const void *p = lua_topointer(L, arg);
           checkformat(L, form, L_FMTFLAGSC, 0);
           if (p == NULL) {  /* avoid calling 'printf' with argument NULL */
             p = "(null)";  /* result */
             form[strlen(form) - 1] = 's';  /* format it as a string */
           }
           nb = l_sprintf(buff, maxitem, form, p);
           break;
         }
         case 'q': {
           if (form[2] != '\0')  /* modifiers? */
             return luaL_error(L, "specifier '%%q' cannot have modifiers");
           addliteral(L, &b, arg);
           break;
         }
         case 's': {
           size_t l;
           const char *s = luaL_tolstring(L, arg, &l);
           if (form[2] == '\0')  /* no modifiers? */
             luaL_addvalue(&b);  /* keep entire string */
           else {
             luaL_argcheck(L, l == strlen(s), arg, "string contains zeros");
             checkformat(L, form, L_FMTFLAGSC, 1);
             if (strchr(form, '.') == NULL && l >= 100) {
               /* no precision and string is too long to be formatted */
               luaL_addvalue(&b);  /* keep entire string */
             }
             else {  /* format the string into 'buff' */
               nb = l_sprintf(buff, maxitem, form, s);
               lua_pop(L, 1);  /* remove result from 'luaL_tolstring' */
             }
           }
           break;
         }
         default: {  /* also treat cases 'pnLlh' */
           return luaL_error(L, "invalid conversion '%s' to 'format'", form);
         }
       }
       lua_assert(cast_uint(nb) < maxitem);
       luaL_addsize(&b, cast_uint(nb));
     }
   }
   luaL_pushresult(&b);
   return 1;
 }
 
 /* }====================================================== */
 
 
 /*
 ** {======================================================
 ** PACK/UNPACK
 ** =======================================================
 */
 
 
 /* value used for padding */
 #if !defined(LUAL_PACKPADBYTE)
 #define LUAL_PACKPADBYTE		0x00
 #endif
 
 /* maximum size for the binary representation of an integer */
 #define MAXINTSIZE	16
 
 /* number of bits in a character */
 #define NB	CHAR_BIT
 
 /* mask for one character (NB 1's) */
 #define MC	((1 << NB) - 1)
 
 /* size of a lua_Integer */
 #define SZINT	((int)sizeof(lua_Integer))
 
 
 /* dummy union to get native endianness */
 static const union {
   int dummy;
   char little;  /* true iff machine is little endian */
 } nativeendian = {1};
 
 
 /*
 ** information to pack/unpack stuff
 */
 typedef struct Header {
   lua_State *L;
   int islittle;
   unsigned maxalign;
 } Header;
 
 
 /*
 ** options for pack/unpack
 */
 typedef enum KOption {
   Kint,		/* signed integers */
   Kuint,	/* unsigned integers */
   Kfloat,	/* single-precision floating-point numbers */
   Knumber,	/* Lua "native" floating-point numbers */
   Kdouble,	/* double-precision floating-point numbers */
   Kchar,	/* fixed-length strings */
   Kstring,	/* strings with prefixed length */
   Kzstr,	/* zero-terminated strings */
   Kpadding,	/* padding */
   Kpaddalign,	/* padding for alignment */
   Knop		/* no-op (configuration or spaces) */
 } KOption;
 
 
 /*
 ** Read an integer numeral from string 'fmt' or return 'df' if
 ** there is no numeral
 */
 static int digit (int c) { return '0' <= c && c <= '9'; }
 
 static size_t getnum (const char **fmt, size_t df) {
   if (!digit(**fmt))  /* no number? */
     return df;  /* return default value */
   else {
     size_t a = 0;
     do {
       a = a*10 + cast_uint(*((*fmt)++) - '0');
     } while (digit(**fmt) && a <= (MAX_SIZE - 9)/10);
     return a;
   }
 }
 
 
 /*
 ** Read an integer numeral and raises an error if it is larger
 ** than the maximum size of integers.
 */
 static unsigned getnumlimit (Header *h, const char **fmt, size_t df) {
   size_t sz = getnum(fmt, df);
   if (l_unlikely((sz - 1u) >= MAXINTSIZE))
     return cast_uint(luaL_error(h->L,
                "integral size (%d) out of limits [1,%d]", sz, MAXINTSIZE));
   return cast_uint(sz);
 }
 
 
 /*
 ** Initialize Header
 */
 static void initheader (lua_State *L, Header *h) {
   h->L = L;
   h->islittle = nativeendian.little;
   h->maxalign = 1;
 }
 
 
 /*
 ** Read and classify next option. 'size' is filled with option's size.
 */
 static KOption getoption (Header *h, const char **fmt, size_t *size) {
   /* dummy structure to get native alignment requirements */
   struct cD { char c; union { LUAI_MAXALIGN; } u; };
   int opt = *((*fmt)++);
   *size = 0;  /* default */
   switch (opt) {
     case 'b': *size = sizeof(char); return Kint;
     case 'B': *size = sizeof(char); return Kuint;
     case 'h': *size = sizeof(short); return Kint;
     case 'H': *size = sizeof(short); return Kuint;
     case 'l': *size = sizeof(long); return Kint;
     case 'L': *size = sizeof(long); return Kuint;
     case 'j': *size = sizeof(lua_Integer); return Kint;
     case 'J': *size = sizeof(lua_Integer); return Kuint;
     case 'T': *size = sizeof(size_t); return Kuint;
     case 'f': *size = sizeof(float); return Kfloat;
     case 'n': *size = sizeof(lua_Number); return Knumber;
     case 'd': *size = sizeof(double); return Kdouble;
     case 'i': *size = getnumlimit(h, fmt, sizeof(int)); return Kint;
     case 'I': *size = getnumlimit(h, fmt, sizeof(int)); return Kuint;
     case 's': *size = getnumlimit(h, fmt, sizeof(size_t)); return Kstring;
     case 'c':
       *size = getnum(fmt, cast_sizet(-1));
       if (l_unlikely(*size == cast_sizet(-1)))
         luaL_error(h->L, "missing size for format option 'c'");
       return Kchar;
     case 'z': return Kzstr;
     case 'x': *size = 1; return Kpadding;
     case 'X': return Kpaddalign;
     case ' ': break;
     case '<': h->islittle = 1; break;
     case '>': h->islittle = 0; break;
     case '=': h->islittle = nativeendian.little; break;
     case '!': {
       const size_t maxalign = offsetof(struct cD, u);
       h->maxalign = getnumlimit(h, fmt, maxalign);
       break;
     }
     default: luaL_error(h->L, "invalid format option '%c'", opt);
   }
   return Knop;
 }
 
 
 /*
 ** Read, classify, and fill other details about the next option.
 ** 'psize' is filled with option's size, 'notoalign' with its
 ** alignment requirements.
 ** Local variable 'size' gets the size to be aligned. (Kpadal option
 ** always gets its full alignment, other options are limited by
 ** the maximum alignment ('maxalign'). Kchar option needs no alignment
 ** despite its size.
 */
 static KOption getdetails (Header *h, size_t totalsize, const char **fmt,
                            size_t *psize, unsigned *ntoalign) {
   KOption opt = getoption(h, fmt, psize);
   size_t align = *psize;  /* usually, alignment follows size */
   if (opt == Kpaddalign) {  /* 'X' gets alignment from following option */
     if (**fmt == '\0' || getoption(h, fmt, &align) == Kchar || align == 0)
       luaL_argerror(h->L, 1, "invalid next option for option 'X'");
   }
   if (align <= 1 || opt == Kchar)  /* need no alignment? */
     *ntoalign = 0;
   else {
     if (align > h->maxalign)  /* enforce maximum alignment */
       align = h->maxalign;
     if (l_unlikely(!ispow2(align)))  /* not a power of 2? */
       luaL_argerror(h->L, 1, "format asks for alignment not power of 2");
     else {
       /* 'szmoda' = totalsize % align */
       unsigned szmoda = cast_uint(totalsize & (align - 1));
       *ntoalign = cast_uint((align - szmoda) & (align - 1));
     }
   }
   return opt;
 }
 
 
 /*
 ** Pack integer 'n' with 'size' bytes and 'islittle' endianness.
 ** The final 'if' handles the case when 'size' is larger than
 ** the size of a Lua integer, correcting the extra sign-extension
 ** bytes if necessary (by default they would be zeros).
 */
 static void packint (luaL_Buffer *b, lua_Unsigned n,
                      int islittle, unsigned size, int neg) {
   char *buff = luaL_prepbuffsize(b, size);
   unsigned i;
   buff[islittle ? 0 : size - 1] = (char)(n & MC);  /* first byte */
   for (i = 1; i < size; i++) {
     n >>= NB;
     buff[islittle ? i : size - 1 - i] = (char)(n & MC);
   }
   if (neg && size > SZINT) {  /* negative number need sign extension? */
     for (i = SZINT; i < size; i++)  /* correct extra bytes */
       buff[islittle ? i : size - 1 - i] = (char)MC;
   }
   luaL_addsize(b, size);  /* add result to buffer */
 }
 
 
 /*
 ** Copy 'size' bytes from 'src' to 'dest', correcting endianness if
 ** given 'islittle' is different from native endianness.
 */
 static void copywithendian (char *dest, const char *src,
                             unsigned size, int islittle) {
   if (islittle == nativeendian.little)
     memcpy(dest, src, size);
   else {
     dest += size - 1;
     while (size-- != 0)
       *(dest--) = *(src++);
   }
 }
 
 
 static int str_pack (lua_State *L) {
   luaL_Buffer b;
   Header h;
   const char *fmt = luaL_checkstring(L, 1);  /* format string */
   int arg = 1;  /* current argument to pack */
   size_t totalsize = 0;  /* accumulate total size of result */
   initheader(L, &h);
   lua_pushnil(L);  /* mark to separate arguments from string buffer */
   luaL_buffinit(L, &b);
   while (*fmt != '\0') {
     unsigned ntoalign;
     size_t size;
     KOption opt = getdetails(&h, totalsize, &fmt, &size, &ntoalign);
     luaL_argcheck(L, size + ntoalign <= MAX_SIZE - totalsize, arg,
                      "result too long");
     totalsize += ntoalign + size;
     while (ntoalign-- > 0)
      luaL_addchar(&b, LUAL_PACKPADBYTE);  /* fill alignment */
     arg++;
     switch (opt) {
       case Kint: {  /* signed integers */
         lua_Integer n = luaL_checkinteger(L, arg);
         if (size < SZINT) {  /* need overflow check? */
           lua_Integer lim = (lua_Integer)1 << ((size * NB) - 1);
           luaL_argcheck(L, -lim <= n && n < lim, arg, "integer overflow");
         }
         packint(&b, (lua_Unsigned)n, h.islittle, cast_uint(size), (n < 0));
         break;
       }
       case Kuint: {  /* unsigned integers */
         lua_Integer n = luaL_checkinteger(L, arg);
         if (size < SZINT)  /* need overflow check? */
           luaL_argcheck(L, (lua_Unsigned)n < ((lua_Unsigned)1 << (size * NB)),
                            arg, "unsigned overflow");
         packint(&b, (lua_Unsigned)n, h.islittle, cast_uint(size), 0);
         break;
       }
       case Kfloat: {  /* C float */
         float f = (float)luaL_checknumber(L, arg);  /* get argument */
         char *buff = luaL_prepbuffsize(&b, sizeof(f));
         /* move 'f' to final result, correcting endianness if needed */
         copywithendian(buff, (char *)&f, sizeof(f), h.islittle);
         luaL_addsize(&b, size);
         break;
       }
       case Knumber: {  /* Lua float */
         lua_Number f = luaL_checknumber(L, arg);  /* get argument */
         char *buff = luaL_prepbuffsize(&b, sizeof(f));
         /* move 'f' to final result, correcting endianness if needed */
         copywithendian(buff, (char *)&f, sizeof(f), h.islittle);
         luaL_addsize(&b, size);
         break;
       }
       case Kdouble: {  /* C double */
         double f = (double)luaL_checknumber(L, arg);  /* get argument */
         char *buff = luaL_prepbuffsize(&b, sizeof(f));
         /* move 'f' to final result, correcting endianness if needed */
         copywithendian(buff, (char *)&f, sizeof(f), h.islittle);
         luaL_addsize(&b, size);
         break;
       }
       case Kchar: {  /* fixed-size string */
         size_t len;
         const char *s = luaL_checklstring(L, arg, &len);
         luaL_argcheck(L, len <= size, arg, "string longer than given size");
         luaL_addlstring(&b, s, len);  /* add string */
         if (len < size) {  /* does it need padding? */
           size_t psize = size - len;  /* pad size */
           char *buff = luaL_prepbuffsize(&b, psize);
           memset(buff, LUAL_PACKPADBYTE, psize);
           luaL_addsize(&b, psize);
         }
         break;
       }
       case Kstring: {  /* strings with length count */
         size_t len;
         const char *s = luaL_checklstring(L, arg, &len);
         luaL_argcheck(L, size >= sizeof(lua_Unsigned) ||
                          len < ((lua_Unsigned)1 << (size * NB)),
                          arg, "string length does not fit in given size");
         /* pack length */
         packint(&b, (lua_Unsigned)len, h.islittle, cast_uint(size), 0);
         luaL_addlstring(&b, s, len);
         totalsize += len;
         break;
       }
       case Kzstr: {  /* zero-terminated string */
         size_t len;
         const char *s = luaL_checklstring(L, arg, &len);
         luaL_argcheck(L, strlen(s) == len, arg, "string contains zeros");
         luaL_addlstring(&b, s, len);
         luaL_addchar(&b, '\0');  /* add zero at the end */
         totalsize += len + 1;
         break;
       }
       case Kpadding: luaL_addchar(&b, LUAL_PACKPADBYTE);  /* FALLTHROUGH */
       case Kpaddalign: case Knop:
         arg--;  /* undo increment */
         break;
     }
   }
   luaL_pushresult(&b);
   return 1;
 }
 
 
 static int str_packsize (lua_State *L) {
   Header h;
   const char *fmt = luaL_checkstring(L, 1);  /* format string */
   size_t totalsize = 0;  /* accumulate total size of result */
   initheader(L, &h);
   while (*fmt != '\0') {
     unsigned ntoalign;
     size_t size;
     KOption opt = getdetails(&h, totalsize, &fmt, &size, &ntoalign);
     luaL_argcheck(L, opt != Kstring && opt != Kzstr, 1,
                      "variable-length format");
     size += ntoalign;  /* total space used by option */
     luaL_argcheck(L, totalsize <= LUA_MAXINTEGER - size,
                      1, "format result too large");
     totalsize += size;
   }
   lua_pushinteger(L, cast_st2S(totalsize));
   return 1;
 }
 
 
 /*
 ** Unpack an integer with 'size' bytes and 'islittle' endianness.
 ** If size is smaller than the size of a Lua integer and integer
 ** is signed, must do sign extension (propagating the sign to the
 ** higher bits); if size is larger than the size of a Lua integer,
 ** it must check the unread bytes to see whether they do not cause an
 ** overflow.
 */
 static lua_Integer unpackint (lua_State *L, const char *str,
                               int islittle, int size, int issigned) {
   lua_Unsigned res = 0;
   int i;
   int limit = (size  <= SZINT) ? size : SZINT;
   for (i = limit - 1; i >= 0; i--) {
     res <<= NB;
     res |= (lua_Unsigned)(unsigned char)str[islittle ? i : size - 1 - i];
   }
   if (size < SZINT) {  /* real size smaller than lua_Integer? */
     if (issigned) {  /* needs sign extension? */
       lua_Unsigned mask = (lua_Unsigned)1 << (size*NB - 1);
       res = ((res ^ mask) - mask);  /* do sign extension */
     }
   }
   else if (size > SZINT) {  /* must check unread bytes */
     int mask = (!issigned || (lua_Integer)res >= 0) ? 0 : MC;
     for (i = limit; i < size; i++) {
       if (l_unlikely((unsigned char)str[islittle ? i : size - 1 - i] != mask))
         luaL_error(L, "%d-byte integer does not fit into Lua Integer", size);
     }
   }
   return (lua_Integer)res;
 }
 
 
 static int str_unpack (lua_State *L) {
   Header h;
   const char *fmt = luaL_checkstring(L, 1);
   size_t ld;
   const char *data = luaL_checklstring(L, 2, &ld);
   size_t pos = posrelatI(luaL_optinteger(L, 3, 1), ld) - 1;
   int n = 0;  /* number of results */
   luaL_argcheck(L, pos <= ld, 3, "initial position out of string");
   initheader(L, &h);
   while (*fmt != '\0') {
     unsigned ntoalign;
     size_t size;
     KOption opt = getdetails(&h, pos, &fmt, &size, &ntoalign);
     luaL_argcheck(L, ntoalign + size <= ld - pos, 2,
                     "data string too short");
     pos += ntoalign;  /* skip alignment */
     /* stack space for item + next position */
     luaL_checkstack(L, 2, "too many results");
     n++;
     switch (opt) {
       case Kint:
       case Kuint: {
         lua_Integer res = unpackint(L, data + pos, h.islittle,
                                        cast_int(size), (opt == Kint));
         lua_pushinteger(L, res);
         break;
       }
       case Kfloat: {
         float f;
         copywithendian((char *)&f, data + pos, sizeof(f), h.islittle);
         lua_pushnumber(L, (lua_Number)f);
         break;
       }
       case Knumber: {
         lua_Number f;
         copywithendian((char *)&f, data + pos, sizeof(f), h.islittle);
         lua_pushnumber(L, f);
         break;
       }
       case Kdouble: {
         double f;
         copywithendian((char *)&f, data + pos, sizeof(f), h.islittle);
         lua_pushnumber(L, (lua_Number)f);
         break;
       }
       case Kchar: {
         lua_pushlstring(L, data + pos, size);
         break;
       }
       case Kstring: {
         lua_Unsigned len = (lua_Unsigned)unpackint(L, data + pos,
                                           h.islittle, cast_int(size), 0);
         luaL_argcheck(L, len <= ld - pos - size, 2, "data string too short");
         lua_pushlstring(L, data + pos + size, len);
         pos += len;  /* skip string */
         break;
       }
       case Kzstr: {
         size_t len = strlen(data + pos);
         luaL_argcheck(L, pos + len < ld, 2,
                          "unfinished string for format 'z'");
         lua_pushlstring(L, data + pos, len);
         pos += len + 1;  /* skip string plus final '\0' */
         break;
       }
       case Kpaddalign: case Kpadding: case Knop:
         n--;  /* undo increment */
         break;
     }
     pos += size;
   }
   lua_pushinteger(L, cast_st2S(pos) + 1);  /* next position */
   return n + 1;
 }
 
 /* }====================================================== */
 
 
 static const luaL_Reg strlib[] = {
   {"byte", str_byte},
   {"char", str_char},
   {"dump", str_dump},
   {"find", str_find},
   {"format", str_format},
   {"gmatch", gmatch},
   {"gsub", str_gsub},
   {"len", str_len},
   {"lower", str_lower},
   {"match", str_match},
   {"rep", str_rep},
   {"reverse", str_reverse},
   {"sub", str_sub},
   {"upper", str_upper},
   {"pack", str_pack},
   {"packsize", str_packsize},
   {"unpack", str_unpack},
   {NULL, NULL}
 };
 
 
 static void createmetatable (lua_State *L) {
   /* table to be metatable for strings */
   luaL_newlibtable(L, stringmetamethods);
   luaL_setfuncs(L, stringmetamethods, 0);
   lua_pushliteral(L, "");  /* dummy string */
   lua_pushvalue(L, -2);  /* copy table */
   lua_setmetatable(L, -2);  /* set table as metatable for strings */
   lua_pop(L, 1);  /* pop dummy string */
   lua_pushvalue(L, -2);  /* get string library */
   lua_setfield(L, -2, "__index");  /* metatable.__index = string */
   lua_pop(L, 1);  /* pop metatable */
 }
 
 
 /*
 ** Open string library
 */
 LUAMOD_API int luaopen_string (lua_State *L) {
   luaL_newlib(L, strlib);
   createmetatable(L);
   return 1;
 }