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detail in string.rep: allow large repetitions of the empty string (no 

possibility of overflows)
This commit is contained in:
Roberto Ierusalimschy 2014-03-12 15:09:06 -03:00
parent 80fe8504f5
commit ad40bb1181
1 changed files with 5 additions and 4 deletions
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9
lstrlib.c
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@ -1,5 +1,5 @@
/* /*
** $Id: lstrlib.c,v 1.185 2014/01/09 16:21:28 roberto Exp roberto $ ** $Id: lstrlib.c,v 1.186 2014/02/25 14:30:21 roberto Exp roberto $
** Standard library for string operations and pattern-matching ** Standard library for string operations and pattern-matching
** See Copyright Notice in lua.h ** See Copyright Notice in lua.h
*/ */
@ -116,7 +116,7 @@ static int str_rep (lua_State *L) {
lua_Integer n = luaL_checkinteger(L, 2); lua_Integer n = luaL_checkinteger(L, 2);
const char *sep = luaL_optlstring(L, 3, "", &lsep); const char *sep = luaL_optlstring(L, 3, "", &lsep);
if (n <= 0) lua_pushliteral(L, ""); if (n <= 0) lua_pushliteral(L, "");
else if (l + lsep < l || l + lsep >= MAXSIZE / n) /* may overflow? */ else if (l + lsep < l || l + lsep > MAXSIZE / n) /* may overflow? */
return luaL_error(L, "resulting string too large"); return luaL_error(L, "resulting string too large");
else { else {
size_t totallen = n * l + (n - 1) * lsep; size_t totallen = n * l + (n - 1) * lsep;
@ -124,8 +124,9 @@ static int str_rep (lua_State *L) {
char *p = luaL_buffinitsize(L, &b, totallen); char *p = luaL_buffinitsize(L, &b, totallen);
while (n-- > 1) { /* first n-1 copies (followed by separator) */ while (n-- > 1) { /* first n-1 copies (followed by separator) */
memcpy(p, s, l * sizeof(char)); p += l; memcpy(p, s, l * sizeof(char)); p += l;
if (lsep > 0) { /* avoid empty 'memcpy' (may be expensive) */ if (lsep > 0) { /* empty 'memcpy' is not that cheap */
memcpy(p, sep, lsep * sizeof(char)); p += lsep; memcpy(p, sep, lsep * sizeof(char));
p += lsep;
} }
} }
memcpy(p, s, l * sizeof(char)); /* last copy (not followed by separator) */ memcpy(p, s, l * sizeof(char)); /* last copy (not followed by separator) */