commit f39034889d010f6f81257dde9517a9ad4d021d1c
parent 6b053a63cb10395d310a043b91bd421656446e78
Author: Roberto Ierusalimschy <roberto@inf.puc-rio.br>
Date: Thu, 28 Oct 2010 13:17:05 -0200
stricter control over number of bits in each operation
Diffstat:
M | lbitlib.c | | | 32 | ++++++++++++++++++++------------ |
1 file changed, 20 insertions(+), 12 deletions(-)
diff --git a/lbitlib.c b/lbitlib.c
@@ -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;
}
+