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allows number of bits used by the library to be changed from outside

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This commit is contained in:
Roberto Ierusalimschy
2010-12-17 11:26:38 -02:00
parent fe0d54d37e
commit 1a92c2b354
1 changed files with 14 additions and 11 deletions
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25
lbitlib.c
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@@ -1,5 +1,5 @@
/* /*
** $Id: lbitlib.c,v 1.13 2010/11/22 18:06:33 roberto Exp roberto $ ** $Id: lbitlib.c,v 1.14 2010/11/29 15:19:28 roberto Exp roberto $
** Standard library for bitwise operations ** Standard library for bitwise operations
** See Copyright Notice in lua.h ** See Copyright Notice in lua.h
*/ */
@@ -14,15 +14,18 @@
/* number of bits to consider in a number */ /* number of bits to consider in a number */
#define NBITS 32 #if !defined(LUA_NBITS)
#define LUA_NBITS 32
#endif
#define ALLONES (~(((~(lua_Unsigned)0) << (NBITS - 1)) << 1))
#define ALLONES (~(((~(lua_Unsigned)0) << (LUA_NBITS - 1)) << 1))
/* macro to trim extra bits */ /* macro to trim extra bits */
#define trim(x) ((x) & ALLONES) #define trim(x) ((x) & ALLONES)
/* builds a number with 'n' ones (1 <= n <= NBITS) */ /* builds a number with 'n' ones (1 <= n <= LUA_NBITS) */
#define mask(n) (~((ALLONES << 1) << ((n) - 1))) #define mask(n) (~((ALLONES << 1) << ((n) - 1)))
@@ -84,11 +87,11 @@ static int b_shift (lua_State *L, b_uint r, int i) {
if (i < 0) { /* shift right? */ if (i < 0) { /* shift right? */
i = -i; i = -i;
r = trim(r); r = trim(r);
if (i >= NBITS) r = 0; if (i >= LUA_NBITS) r = 0;
else r >>= i; else r >>= i;
} }
else { /* shift left */ else { /* shift left */
if (i >= NBITS) r = 0; if (i >= LUA_NBITS) r = 0;
else r <<= i; else r <<= i;
r = trim(r); r = trim(r);
} }
@@ -110,10 +113,10 @@ static int b_rshift (lua_State *L) {
static int b_arshift (lua_State *L) { static int b_arshift (lua_State *L) {
b_uint r = luaL_checkunsigned(L, 1); b_uint r = luaL_checkunsigned(L, 1);
int i = luaL_checkint(L, 2); int i = luaL_checkint(L, 2);
if (i < 0 || !(r & ((b_uint)1 << (NBITS - 1)))) if (i < 0 || !(r & ((b_uint)1 << (LUA_NBITS - 1))))
return b_shift(L, r, -i); return b_shift(L, r, -i);
else { /* arithmetic shift for 'negative' number */ else { /* arithmetic shift for 'negative' number */
if (i >= NBITS) r = ALLONES; if (i >= LUA_NBITS) r = ALLONES;
else else
r = trim((r >> i) | ~(~(b_uint)0 >> i)); /* add signal bit */ r = trim((r >> i) | ~(~(b_uint)0 >> i)); /* add signal bit */
lua_pushunsigned(L, r); lua_pushunsigned(L, r);
@@ -124,9 +127,9 @@ static int b_arshift (lua_State *L) {
static int b_rot (lua_State *L, int i) { static int b_rot (lua_State *L, int i) {
b_uint r = luaL_checkunsigned(L, 1); b_uint r = luaL_checkunsigned(L, 1);
i &= (NBITS - 1); /* i = i % NBITS */ i &= (LUA_NBITS - 1); /* i = i % NBITS */
r = trim(r); r = trim(r);
r = (r << i) | (r >> (NBITS - i)); r = (r << i) | (r >> (LUA_NBITS - i));
lua_pushunsigned(L, trim(r)); lua_pushunsigned(L, trim(r));
return 1; return 1;
} }
@@ -151,7 +154,7 @@ static int fieldargs (lua_State *L, int farg, int *width) {
int w = luaL_optint(L, farg + 1, 1); int w = luaL_optint(L, farg + 1, 1);
luaL_argcheck(L, 0 <= f, farg, "field cannot be netative"); luaL_argcheck(L, 0 <= f, farg, "field cannot be netative");
luaL_argcheck(L, 0 < w, farg + 1, "width must be positive"); luaL_argcheck(L, 0 < w, farg + 1, "width must be positive");
if (f + w > NBITS) if (f + w > LUA_NBITS)
luaL_error(L, "trying to access non-existent bits"); luaL_error(L, "trying to access non-existent bits");
*width = w; *width = w;
return f; return f;