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avoid constant overflow when shifting left signed integers until

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their last bit
This commit is contained in:
Roberto Ierusalimschy 2014-04-03 10:29:24 -03:00
parent 3a044de5a1
commit 48c745a611
1 changed files with 5 additions and 5 deletions
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10
lstrlib.c
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@ -1,5 +1,5 @@
/* /*
** $Id: lstrlib.c,v 1.190 2014/03/27 15:58:05 roberto Exp roberto $ ** $Id: lstrlib.c,v 1.191 2014/03/31 18:38:26 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
*/ */
@ -954,10 +954,10 @@ static int str_format (lua_State *L) {
#define NB CHAR_BIT #define NB CHAR_BIT
/* mask for one character (NB ones) */ /* mask for one character (NB ones) */
#define MC (((lua_Integer)1 << NB) - 1) #define MC ((1 << NB) - 1)
/* mask for one character without sign ((NB - 1) ones) */ /* mask for one character without sign ((NB - 1) ones) */
#define SM (((lua_Integer)1 << (NB - 1)) - 1) #define SM ((1 << (NB - 1)) - 1)
#define SZINT ((int)sizeof(lua_Integer)) #define SZINT ((int)sizeof(lua_Integer))
@ -1007,7 +1007,7 @@ static int packint (char *buff, lua_Integer n, int littleendian, int size) {
/* test for overflow: OK if there are only zeros left in higher bytes, /* test for overflow: OK if there are only zeros left in higher bytes,
or if there are only ones left and packed number is negative (signal or if there are only ones left and packed number is negative (signal
bit, the higher bit in last byte, is one) */ bit, the higher bit in last byte, is one) */
return ((n & ~MC) == 0 || (n | SM) == ~(lua_Integer)0); return ((n & ~(lua_Integer)MC) == 0 || (n | SM) == ~(lua_Integer)0);
} }
@ -1025,7 +1025,7 @@ static int packint_l (lua_State *L) {
/* mask to check higher-order byte in a Lua integer */ /* mask to check higher-order byte in a Lua integer */
#define HIGHERBYTE (MC << (NB * (SZINT - 1))) #define HIGHERBYTE ((lua_Unsigned)MC << (NB * (SZINT - 1)))
/* mask to check higher-order byte + signal bit of next (lower) byte */ /* mask to check higher-order byte + signal bit of next (lower) byte */
#define HIGHERBYTE1 (HIGHERBYTE | (HIGHERBYTE >> 1)) #define HIGHERBYTE1 (HIGHERBYTE | (HIGHERBYTE >> 1))