commit 12bd01c56710d957e28bea41aab9f9b98182e72b
parent 626124d2d8ae582c3444a9e0e11b09f31dc098ff
Author: Roberto Ierusalimschy <roberto@inf.puc-rio.br>
Date: Mon, 12 May 2014 16:13:07 -0300
added comments to several functions
Diffstat:
| M | lvm.c | | | 148 | ++++++++++++++++++++++++++++++++++++++++++++++++++----------------------------- |
1 file changed, 93 insertions(+), 55 deletions(-)
diff --git a/lvm.c b/lvm.c
@@ -1,5 +1,5 @@
/*
-** $Id: lvm.c,v 2.205 2014/05/01 18:18:06 roberto Exp roberto $
+** $Id: lvm.c,v 2.206 2014/05/09 14:20:52 roberto Exp roberto $
** Lua virtual machine
** See Copyright Notice in lua.h
*/
@@ -56,7 +56,8 @@ static int tofloat (const TValue *obj, lua_Number *n) {
/*
-** Try to convert a value to a float
+** Try to convert a value to a float. Check 'isinteger' first, because
+** in general the float case is already handled by the macro 'tonumber'.
*/
int luaV_tonumber_ (const TValue *obj, lua_Number *n) {
TValue v;
@@ -69,7 +70,7 @@ int luaV_tonumber_ (const TValue *obj, lua_Number *n) {
*n = fltvalue(obj);
return 1;
}
- else if (ttisstring(obj) &&
+ else if (ttisstring(obj) && /* string convertible to number? */
luaO_str2num(svalue(obj), &v) == tsvalue(obj)->len + 1) {
obj = &v;
goto again; /* convert result from 'luaO_str2num' to a float */
@@ -178,8 +179,12 @@ static int forlimit (const TValue *obj, lua_Integer *p, lua_Integer step,
}
+/*
+** Main function for table access (invoking metamethods if needed).
+** Compute 'val = t[key]'
+*/
void luaV_gettable (lua_State *L, const TValue *t, TValue *key, StkId val) {
- int loop;
+ int loop; /* counter to avoid infinite loops */
for (loop = 0; loop < MAXTAGLOOP; loop++) {
const TValue *tm;
if (ttistable(t)) { /* `t' is a table? */
@@ -187,32 +192,36 @@ void luaV_gettable (lua_State *L, const TValue *t, TValue *key, StkId val) {
const TValue *res = luaH_get(h, key); /* do a primitive get */
if (!ttisnil(res) || /* result is not nil? */
(tm = fasttm(L, h->metatable, TM_INDEX)) == NULL) { /* or no TM? */
- setobj2s(L, val, res);
+ setobj2s(L, val, res); /* result is the raw get */
return;
}
- /* else will try the tag method */
+ /* else will try metamethod */
}
else if (ttisnil(tm = luaT_gettmbyobj(L, t, TM_INDEX)))
- luaG_typeerror(L, t, "index");
- if (ttisfunction(tm)) {
+ luaG_typeerror(L, t, "index"); /* no metamethod */
+ if (ttisfunction(tm)) { /* metamethod is a function */
luaT_callTM(L, tm, t, key, val, 1);
return;
}
- t = tm; /* else repeat with 'tm' */
+ t = tm; /* else repeat access over 'tm' */
}
luaG_runerror(L, "gettable chain too long; possible loop");
}
+/*
+** Main function for table assignment (invoking metamethods if needed).
+** Compute 't[key] = val'
+*/
void luaV_settable (lua_State *L, const TValue *t, TValue *key, StkId val) {
- int loop;
+ int loop; /* counter to avoid infinite loops */
for (loop = 0; loop < MAXTAGLOOP; loop++) {
const TValue *tm;
if (ttistable(t)) { /* `t' is a table? */
Table *h = hvalue(t);
TValue *oldval = cast(TValue *, luaH_get(h, key));
/* if previous value is not nil, there must be a previous entry
- in the table; moreover, a metamethod has no relevance */
+ in the table; a metamethod has no relevance */
if (!ttisnil(oldval) ||
/* previous value is nil; must check the metamethod */
((tm = fasttm(L, h->metatable, TM_NEWINDEX)) == NULL &&
@@ -232,32 +241,40 @@ void luaV_settable (lua_State *L, const TValue *t, TValue *key, StkId val) {
else /* not a table; check metamethod */
if (ttisnil(tm = luaT_gettmbyobj(L, t, TM_NEWINDEX)))
luaG_typeerror(L, t, "index");
- /* there is a metamethod */
+ /* try the metamethod */
if (ttisfunction(tm)) {
luaT_callTM(L, tm, t, key, val, 0);
return;
}
- t = tm; /* else repeat with 'tm' */
+ t = tm; /* else repeat assginment over 'tm' */
}
luaG_runerror(L, "settable chain too long; possible loop");
}
+/*
+** Compare two strings 'ls' x 'rs', returning an integer smaller-equal-
+** -larger than zero if 'ls' is smaller-equal-larger than 'rs'.
+** The code is a little tricky because it allows '\0' in the strings
+** and it uses 'strcoll' (to respect locales) for each segments
+** of the strings.
+*/
static int l_strcmp (const TString *ls, const TString *rs) {
const char *l = getstr(ls);
size_t ll = ls->tsv.len;
const char *r = getstr(rs);
size_t lr = rs->tsv.len;
- for (;;) {
+ for (;;) { /* for each segment */
int temp = strcoll(l, r);
- if (temp != 0) return temp;
- else { /* strings are equal up to a `\0' */
+ if (temp != 0) /* not equal? */
+ return temp; /* done */
+ else { /* strings are equal up to a '\0' */
size_t len = strlen(l); /* index of first `\0' in both strings */
- if (len == lr) /* r is finished? */
- return (len == ll) ? 0 : 1;
- else if (len == ll) /* l is finished? */
- return -1; /* l is smaller than r (because r is not finished) */
- /* both strings longer than `len'; go on comparing (after the `\0') */
+ if (len == lr) /* 'rs' is finished? */
+ return (len == ll) ? 0 : 1; /* check 'ls' */
+ else if (len == ll) /* 'ls' is finished? */
+ return -1; /* 'ls' is smaller than 'rs' ('rs' is not finished) */
+ /* both strings longer than `len'; go on comparing after the '\0' */
len++;
l += len; ll -= len; r += len; lr -= len;
}
@@ -265,29 +282,35 @@ static int l_strcmp (const TString *ls, const TString *rs) {
}
+/*
+** Main operation less than; return 'l < r'.
+*/
int luaV_lessthan (lua_State *L, const TValue *l, const TValue *r) {
int res;
lua_Number nl, nr;
- if (ttisinteger(l) && ttisinteger(r))
+ if (ttisinteger(l) && ttisinteger(r)) /* both operands are integers? */
return (ivalue(l) < ivalue(r));
- else if (tofloat(l, &nl) && tofloat(r, &nr))
+ else if (tofloat(l, &nl) && tofloat(r, &nr)) /* both are numbers? */
return luai_numlt(nl, nr);
- else if (ttisstring(l) && ttisstring(r))
+ else if (ttisstring(l) && ttisstring(r)) /* both are strings? */
return l_strcmp(rawtsvalue(l), rawtsvalue(r)) < 0;
- else if ((res = luaT_callorderTM(L, l, r, TM_LT)) < 0)
- luaG_ordererror(L, l, r);
+ else if ((res = luaT_callorderTM(L, l, r, TM_LT)) < 0) /* no metamethod? */
+ luaG_ordererror(L, l, r); /* error */
return res;
}
+/*
+** Main operation less than or equal to; return 'l <= r'.
+*/
int luaV_lessequal (lua_State *L, const TValue *l, const TValue *r) {
int res;
lua_Number nl, nr;
- if (ttisinteger(l) && ttisinteger(r))
+ if (ttisinteger(l) && ttisinteger(r)) /* both operands are integers? */
return (ivalue(l) <= ivalue(r));
- else if (tofloat(l, &nl) && tofloat(r, &nr))
+ else if (tofloat(l, &nl) && tofloat(r, &nr)) /* both are numbers? */
return luai_numle(nl, nr);
- else if (ttisstring(l) && ttisstring(r))
+ else if (ttisstring(l) && ttisstring(r)) /* both are strings? */
return l_strcmp(rawtsvalue(l), rawtsvalue(r)) <= 0;
else if ((res = luaT_callorderTM(L, l, r, TM_LE)) >= 0) /* first try `le' */
return res;
@@ -298,15 +321,16 @@ int luaV_lessequal (lua_State *L, const TValue *l, const TValue *r) {
/*
-** equality of Lua values. L == NULL means raw equality (no metamethods)
+** Main operation for equality of Lua values; return 't1 == t2'.
+** L == NULL means raw equality (no metamethods)
*/
int luaV_equalobj (lua_State *L, const TValue *t1, const TValue *t2) {
const TValue *tm;
- if (ttype(t1) != ttype(t2)) {
+ if (ttype(t1) != ttype(t2)) { /* not the same variant? */
if (ttnov(t1) != ttnov(t2) || ttnov(t1) != LUA_TNUMBER)
return 0; /* only numbers can be equal with different variants */
else { /* two numbers with different variants */
- lua_Number n1, n2;
+ lua_Number n1, n2; /* compare them as floats */
lua_assert(ttisnumber(t1) && ttisnumber(t2));
cast_void(tofloat(t1, &n1)); cast_void(tofloat(t2, &n2));
return luai_numeq(n1, n2);
@@ -343,8 +367,13 @@ int luaV_equalobj (lua_State *L, const TValue *t1, const TValue *t2) {
}
+/* macro used by 'luaV_concat' to ensure that element at 'o' is a string */
#define tostring(L,o) (ttisstring(o) || (luaV_tostring(L, o)))
+/*
+** Main operation for concatenation: concat 'total' values in the stack,
+** from 'L->top - total' up to 'L->top - 1'.
+*/
void luaV_concat (lua_State *L, int total) {
lua_assert(total >= 2);
do {
@@ -372,12 +401,12 @@ void luaV_concat (lua_State *L, int total) {
buffer = luaZ_openspace(L, &G(L)->buff, tl);
tl = 0;
n = i;
- do { /* concat all strings */
+ do { /* copy all strings to buffer */
size_t l = tsvalue(top-i)->len;
memcpy(buffer+tl, svalue(top-i), l * sizeof(char));
tl += l;
} while (--i > 0);
- setsvalue2s(L, top-n, luaS_newlstr(L, buffer, tl));
+ setsvalue2s(L, top-n, luaS_newlstr(L, buffer, tl)); /* create result */
}
total -= n-1; /* got 'n' strings to create 1 new */
L->top -= n-1; /* popped 'n' strings and pushed one */
@@ -385,6 +414,9 @@ void luaV_concat (lua_State *L, int total) {
}
+/*
+** Main operation 'ra' = #rb'.
+*/
void luaV_objlen (lua_State *L, StkId ra, const TValue *rb) {
const TValue *tm;
switch (ttnov(rb)) {
@@ -410,15 +442,18 @@ void luaV_objlen (lua_State *L, StkId ra, const TValue *rb) {
}
-lua_Integer luaV_div (lua_State *L, lua_Integer x, lua_Integer y) {
- if (l_castS2U(y) + 1u <= 1u) { /* special cases: -1 or 0 */
- if (y == 0)
+/*
+** Integer division; return 'm // n'.
+*/
+lua_Integer luaV_div (lua_State *L, lua_Integer m, lua_Integer n) {
+ if (l_castS2U(n) + 1u <= 1u) { /* special cases: -1 or 0 */
+ if (n == 0)
luaG_runerror(L, "attempt to divide by zero");
- return intop(-, 0, x); /* y==-1; avoid overflow with 0x80000...//-1 */
+ return intop(-, 0, m); /* n==-1; avoid overflow with 0x80000...//-1 */
}
else {
- lua_Integer d = x / y; /* perform division */
- if ((x ^ y) >= 0 || x % y == 0) /* same signal or no rest? */
+ lua_Integer d = m / n; /* perform division */
+ if ((m ^ n) >= 0 || m % n == 0) /* same signal or no rest? */
return d;
else
return d - 1; /* correct 'div' for negative case */
@@ -426,33 +461,36 @@ lua_Integer luaV_div (lua_State *L, lua_Integer x, lua_Integer y) {
}
-lua_Integer luaV_mod (lua_State *L, lua_Integer x, lua_Integer y) {
- if (l_castS2U(y) + 1u <= 1u) { /* special cases: -1 or 0 */
- if (y == 0)
+/*
+** Integer modulus; return 'm % n'.
+*/
+lua_Integer luaV_mod (lua_State *L, lua_Integer m, lua_Integer n) {
+ if (l_castS2U(n) + 1u <= 1u) { /* special cases: -1 or 0 */
+ if (n == 0)
luaG_runerror(L, "attempt to perform 'n%%0'");
- return 0; /* y==-1; avoid overflow with 0x80000...%-1 */
+ return 0; /* m % -1 == 0; avoid overflow with 0x80000...%-1 */
}
else {
- lua_Integer r = x % y;
- if (r == 0 || (x ^ y) >= 0)
+ lua_Integer r = m % n;
+ if (r == 0 || (m ^ n) >= 0)
return r;
else
- return r + y; /* correct 'mod' for negative case */
+ return r + n; /* correct 'mod' for negative case */
}
}
-lua_Integer luaV_pow (lua_Integer x, lua_Integer y) {
- lua_assert(y >= 0);
- if (y == 0)
- return 1; /* x^0 == 1 */
+lua_Integer luaV_pow (lua_Integer m, lua_Integer n) {
+ lua_assert(n >= 0);
+ if (n == 0)
+ return 1; /* m^0 == 1 */
else {
lua_Integer r = 1;
- for (; y > 1; y >>= 1) {
- if (y & 1) r = intop(*, r, x);
- x = intop(*, x, x);
+ for (; n > 1; n >>= 1) {
+ if (n & 1) r = intop(*, r, m);
+ m = intop(*, m, m);
}
- r = intop(*, r, x);
+ r = intop(*, r, m);
return r;
}
}
