commit 7f4906f565ab9f8b1125107a3abae3d759f3ecf2
parent b8a9d14032b717f6e5c493a9ec20e3494c9f82a0
Author: Roberto Ierusalimschy <roberto@inf.puc-rio.br>
Date: Wed, 8 Nov 2023 13:24:11 -0300
Towards external strings
Long strings have a pointer to string contents.
Diffstat:
4 files changed, 36 insertions(+), 22 deletions(-)
diff --git a/lgc.c b/lgc.c
@@ -808,12 +808,12 @@ static void freeobj (lua_State *L, GCObject *o) {
case LUA_VSHRSTR: {
TString *ts = gco2ts(o);
luaS_remove(L, ts); /* remove it from hash table */
- luaM_freemem(L, ts, sizelstring(ts->shrlen));
+ luaM_freemem(L, ts, sizestrshr(ts->shrlen));
break;
}
case LUA_VLNGSTR: {
TString *ts = gco2ts(o);
- luaM_freemem(L, ts, sizelstring(ts->u.lnglen));
+ luaM_freemem(L, ts, sizestrlng(ts->u.lnglen));
break;
}
default: lua_assert(0);
diff --git a/lobject.h b/lobject.h
@@ -388,35 +388,38 @@ typedef struct GCObject {
typedef struct TString {
CommonHeader;
lu_byte extra; /* reserved words for short strings; "has hash" for longs */
- lu_byte shrlen; /* length for short strings, 0xFF for long strings */
+ ls_byte shrlen; /* length for short strings, negative for long strings */
unsigned int hash;
union {
size_t lnglen; /* length for long strings */
struct TString *hnext; /* linked list for hash table */
} u;
- char contents[1]; /* string body starts here */
+ char *contents; /* pointer to content in long strings */
} TString;
+#define strisshr(ts) ((ts)->shrlen >= 0)
+
/*
** Get the actual string (array of bytes) from a 'TString'. (Generic
** version and specialized versions for long and short strings.)
*/
-#define getlngstr(ts) check_exp((ts)->shrlen == 0xFF, (ts)->contents)
-#define getshrstr(ts) check_exp((ts)->shrlen != 0xFF, (ts)->contents)
-#define getstr(ts) ((ts)->contents)
+#define rawgetshrstr(ts) (cast_charp(&(ts)->contents))
+#define getshrstr(ts) check_exp(strisshr(ts), rawgetshrstr(ts))
+#define getlngstr(ts) check_exp(!strisshr(ts), (ts)->contents)
+#define getstr(ts) (strisshr(ts) ? rawgetshrstr(ts) : (ts)->contents)
-/* get string length from 'TString *s' */
-#define tsslen(s) \
- ((s)->shrlen != 0xFF ? (s)->shrlen : (s)->u.lnglen)
+/* get string length from 'TString *ts' */
+#define tsslen(ts) \
+ (strisshr(ts) ? cast_uint((ts)->shrlen) : (ts)->u.lnglen)
/*
** Get string and length */
#define getlstr(ts, len) \
- ((ts)->shrlen != 0xFF \
- ? (cast_void(len = (ts)->shrlen), (ts)->contents) \
+ (strisshr(ts) \
+ ? (cast_void(len = (ts)->shrlen), rawgetshrstr(ts)) \
: (cast_void(len = (ts)->u.lnglen), (ts)->contents))
/* }================================================================== */
diff --git a/lstring.c b/lstring.c
@@ -140,24 +140,25 @@ void luaS_init (lua_State *L) {
/*
** creates a new string object
*/
-static TString *createstrobj (lua_State *L, size_t l, int tag, unsigned int h) {
+static TString *createstrobj (lua_State *L, size_t totalsize, int tag,
+ unsigned int h) {
TString *ts;
GCObject *o;
- size_t totalsize; /* total size of TString object */
- totalsize = sizelstring(l);
o = luaC_newobj(L, tag, totalsize);
ts = gco2ts(o);
ts->hash = h;
ts->extra = 0;
- getstr(ts)[l] = '\0'; /* ending 0 */
return ts;
}
TString *luaS_createlngstrobj (lua_State *L, size_t l) {
- TString *ts = createstrobj(L, l, LUA_VLNGSTR, G(L)->seed);
+ size_t totalsize = sizestrlng(l);
+ TString *ts = createstrobj(L, totalsize, LUA_VLNGSTR, G(L)->seed);
ts->u.lnglen = l;
- ts->shrlen = 0xFF; /* signals that it is a long string */
+ ts->shrlen = -1; /* signals that it is a long string */
+ ts->contents = cast_charp(ts) + sizeof(TString);
+ ts->contents[l] = '\0'; /* ending 0 */
return ts;
}
@@ -194,7 +195,8 @@ static TString *internshrstr (lua_State *L, const char *str, size_t l) {
TString **list = &tb->hash[lmod(h, tb->size)];
lua_assert(str != NULL); /* otherwise 'memcmp'/'memcpy' are undefined */
for (ts = *list; ts != NULL; ts = ts->u.hnext) {
- if (l == ts->shrlen && (memcmp(str, getshrstr(ts), l * sizeof(char)) == 0)) {
+ if (l == cast_uint(ts->shrlen) &&
+ (memcmp(str, getshrstr(ts), l * sizeof(char)) == 0)) {
/* found! */
if (isdead(g, ts)) /* dead (but not collected yet)? */
changewhite(ts); /* resurrect it */
@@ -206,8 +208,9 @@ static TString *internshrstr (lua_State *L, const char *str, size_t l) {
growstrtab(L, tb);
list = &tb->hash[lmod(h, tb->size)]; /* rehash with new size */
}
- ts = createstrobj(L, l, LUA_VSHRSTR, h);
+ ts = createstrobj(L, sizestrshr(l), LUA_VSHRSTR, h);
ts->shrlen = cast_byte(l);
+ getshrstr(ts)[l] = '\0'; /* ending 0 */
memcpy(getshrstr(ts), str, l * sizeof(char));
ts->u.hnext = *list;
*list = ts;
diff --git a/lstring.h b/lstring.h
@@ -20,10 +20,18 @@
/*
-** Size of a TString: Size of the header plus space for the string
+** Size of a short TString: Size of the header plus space for the string
** itself (including final '\0').
*/
-#define sizelstring(l) (offsetof(TString, contents) + ((l) + 1) * sizeof(char))
+#define sizestrshr(l) \
+ (offsetof(TString, contents) + ((l) + 1) * sizeof(char))
+
+/*
+** Size of a long TString: Size of the header plus space for the string
+** itself (including final '\0').
+*/
+#define sizestrlng(l) (sizeof(TString) + ((l) + 1) * sizeof(char))
+
#define luaS_newliteral(L, s) (luaS_newlstr(L, "" s, \
(sizeof(s)/sizeof(char))-1))
