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avoid overflows in computation of step size

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This commit is contained in:
Roberto Ierusalimschy
2017-06-01 16:16:34 -03:00
parent 8821746841
commit 4bc33d64de
2 changed files with 12 additions and 3 deletions
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6
lgc.c
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@@ -1,5 +1,5 @@
/*
** $Id: lgc.c,v 2.228 2017/05/04 13:32:01 roberto Exp roberto $
** $Id: lgc.c,v 2.229 2017/05/26 19:14:29 roberto Exp roberto $
** Garbage Collector
** See Copyright Notice in lua.h
*/
@@ -1486,7 +1486,9 @@ void luaC_runtilstate (lua_State *L, int statesmask) {
static void incstep (lua_State *L, global_State *g) {
int stepmul = (g->gcstepmul | 1); /* avoid division by 0 */
l_mem debt = (g->GCdebt / WORK2MEM) * stepmul;
l_mem stepsize = cast(l_mem, 1) << g->gcstepsize;
l_mem stepsize = (g->gcstepsize <= log2maxs(l_mem))
? cast(l_mem, 1) << g->gcstepsize
: MAX_LMEM;
stepsize = -((stepsize / WORK2MEM) * stepmul);
do { /* repeat until pause or enough "credit" (negative debt) */
lu_mem work = singlestep(L); /* perform one single step */

9
llimits.h
View File

@@ -1,5 +1,5 @@
/*
** $Id: llimits.h,v 1.141 2015/11/19 19:16:22 roberto Exp roberto $
** $Id: llimits.h,v 1.142 2017/04/24 18:06:12 roberto Exp roberto $
** Limits, basic types, and some other 'installation-dependent' definitions
** See Copyright Notice in lua.h
*/
@@ -51,6 +51,13 @@ typedef unsigned char lu_byte;
#define MAX_INT INT_MAX /* maximum value of an int */
/*
** floor of the log2 of the maximum signed value for integral type 't'.
** (That is, maximum 'n' such that '2^n' fits in the given signed type.)
*/
#define log2maxs(t) (sizeof(t) * 8 - 2)
/*
** conversion of pointer to unsigned integer:
** this is for hashing only; there is no problem if the integer