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stricter control over number of bits in each operation

This commit is contained in:
Roberto Ierusalimschy 2010-10-28 13:17:29 -02:00
parent 6b053a63cb
commit f39034889d
1 changed files with 20 additions and 12 deletions
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32
lbitlib.c
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@ -1,5 +1,5 @@
/*
** $Id: lbitlib.c,v 1.8 2010/10/25 20:31:11 roberto Exp roberto $
** $Id: lbitlib.c,v 1.9 2010/10/27 16:50:32 roberto Exp roberto $
** Standard library for bitwise operations
** See Copyright Notice in lua.h
*/
@ -13,12 +13,16 @@
#include "lualib.h"
/* number of bits considered when shifting/rotating (must be a power of 2) */
/* number of bits to consider in a number */
#define NBITS 32
#define ALLONES (~(((~(lua_Unsigned)0) << (NBITS - 1)) << 1))
typedef LUA_INT32 b_int;
typedef unsigned LUA_INT32 b_uint;
/* mask to trim extra bits */
#define trim(x) ((x) & ALLONES)
typedef lua_Unsigned b_uint;
#define getuintarg(L,arg) luaL_checkunsigned(L,arg)
@ -29,7 +33,7 @@ static b_uint andaux (lua_State *L) {
b_uint r = ~(b_uint)0;
for (i = 1; i <= n; i++)
r &= getuintarg(L, i);
return r;
return trim(r);
}
@ -52,7 +56,7 @@ static int b_or (lua_State *L) {
b_uint r = 0;
for (i = 1; i <= n; i++)
r |= getuintarg(L, i);
lua_pushunsigned(L, r);
lua_pushunsigned(L, trim(r));
return 1;
}
@ -62,14 +66,14 @@ static int b_xor (lua_State *L) {
b_uint r = 0;
for (i = 1; i <= n; i++)
r ^= getuintarg(L, i);
lua_pushunsigned(L, r);
lua_pushunsigned(L, trim(r));
return 1;
}
static int b_not (lua_State *L) {
b_uint r = ~getuintarg(L, 1);
lua_pushunsigned(L, r);
lua_pushunsigned(L, trim(r));
return 1;
}
@ -77,12 +81,14 @@ static int b_not (lua_State *L) {
static int b_shift (lua_State *L, b_uint r, int i) {
if (i < 0) { /* shift right? */
i = -i;
r = trim(r);
if (i >= NBITS) r = 0;
else r >>= i;
}
else { /* shift left */
if (i >= NBITS) r = 0;
else r <<= i;
r = trim(r);
}
lua_pushunsigned(L, r);
return 1;
@ -102,12 +108,12 @@ static int b_rshift (lua_State *L) {
static int b_arshift (lua_State *L) {
b_uint r = getuintarg(L, 1);
int i = luaL_checkint(L, 2);
if (i < 0 || !(r & 0x80000000))
if (i < 0 || !(r & (1 << (NBITS - 1))))
return b_shift(L, r, -i);
else { /* arithmetic shift for 'negative' number */
if (i >= NBITS) r = 0xffffffff;
if (i >= NBITS) r = ALLONES;
else
r = (r >> i) | ~(~(b_uint)0 >> i); /* add signal bit */
r = trim((r >> i) | ~(~(b_uint)0 >> i)); /* add signal bit */
lua_pushunsigned(L, r);
return 1;
}
@ -117,8 +123,9 @@ static int b_arshift (lua_State *L) {
static int b_rot (lua_State *L, int i) {
b_uint r = getuintarg(L, 1);
i &= (NBITS - 1); /* i = i % NBITS */
r = trim(r);
r = (r << i) | (r >> (NBITS - i));
lua_pushunsigned(L, r);
lua_pushunsigned(L, trim(r));
return 1;
}
@ -153,3 +160,4 @@ LUAMOD_API int luaopen_bit32 (lua_State *L) {
luaL_newlib(L, bitlib);
return 1;
}