lbitlib.c

/* Bitwise operations library */
/* (c) Reuben Thomas 2000-2008 */
/* See README for license */

#include <lua.h>
#include <lauxlib.h>
#include <limits.h>

#include "bit_limits.h"


/* FIXME: Assumes lua_Integer is ptrdiff_t */
#define LUA_INTEGER_MAX PTRDIFF_MAX
#define LUA_INTEGER_MIN PTRDIFF_MIN

/* FIXME: Assumes size_t is an unsigned lua_Integer */
typedef size_t lua_UInteger;
#define LUA_UINTEGER_MAX SIZE_MAX


/* Bit type size and limits */

#define BIT_BITS                                                        \
  (CHAR_BIT * sizeof(lua_Integer) > BITLIB_FLOAT_BITS ?                 \
   BITLIB_FLOAT_BITS : (CHAR_BIT * sizeof(lua_Integer)))

/* This code may give warnings if BITLIB_FLOAT_* are too big to fit in
   long, but that doesn't matter since in that case they won't be
   used. */
#define BIT_MAX                                                         \
  (CHAR_BIT * sizeof(lua_Integer) > BITLIB_FLOAT_BITS ? BITLIB_FLOAT_MAX : LUA_INTEGER_MAX)

#define BIT_MIN                                                         \
  (CHAR_BIT * sizeof(lua_Integer) > BITLIB_FLOAT_BITS ? BITLIB_FLOAT_MIN : LUA_INTEGER_MIN)

#define BIT_UMAX                                                        \
  (CHAR_BIT * sizeof(lua_Integer) > BITLIB_FLOAT_BITS ? BITLIB_FLOAT_UMAX : LUA_UINTEGER_MAX)


/* Define TOBIT to get a bit value */
#ifdef BUILTIN_CAST
#define
#define TOBIT(L, n, res)                    \
  ((void)(res), luaL_checkinteger((L), (n)))
#else
#include <stdint.h>
#include <math.h>

/* FIXME: Assumes lua_Number fits in a double (use of fmod). */
#define TOBIT(L, n, res)                                            \
  ((lua_Integer)(((res) = fmod(luaL_checknumber(L, (n)), (double)BIT_UMAX + 1.0)), \
                 (res) > BIT_MAX ? ((res) -= (double)BIT_UMAX, (res) -= 1) : \
                 ((res) < BIT_MIN ? ((res) += (double)BIT_UMAX, (res) += 1) : (res))))
#endif


#define BIT_TRUNCATE(i)                         \
  ((i) & BIT_UMAX)


/* Operations

   The macros MONADIC and VARIADIC only deal with bitwise operations.

   LOGICAL_SHIFT truncates its left-hand operand before shifting so
   that any extra bits at the most-significant end are not shifted
   into the result.

   ARITHMETIC_SHIFT does not truncate its left-hand operand, so that
   the sign bits are not removed and right shift work properly.
   */

#define MONADIC(name, op)                                       \
  static int bit_ ## name(lua_State *L) {                       \
    lua_Number f;                                               \
    lua_pushinteger(L, BIT_TRUNCATE(op TOBIT(L, 1, f)));        \
    return 1;                                                   \
  }

#define VARIADIC(name, op)                      \
  static int bit_ ## name(lua_State *L) {       \
    lua_Number f;                               \
    int n = lua_gettop(L), i;                   \
    lua_Integer w = TOBIT(L, 1, f);             \
    for (i = 2; i <= n; i++)                    \
      w op TOBIT(L, i, f);                      \
    lua_pushinteger(L, BIT_TRUNCATE(w));        \
    return 1;                                   \
  }

#define LOGICAL_SHIFT(name, op)                                         \
  static int bit_ ## name(lua_State *L) {                               \
    lua_Number f;                                                       \
    lua_pushinteger(L, BIT_TRUNCATE(BIT_TRUNCATE((lua_UInteger)TOBIT(L, 1, f)) op \
                                    (unsigned)luaL_checknumber(L, 2))); \
    return 1;                                                           \
  }

#define ARITHMETIC_SHIFT(name, op)                                      \
  static int bit_ ## name(lua_State *L) {                               \
    lua_Number f;                                                       \
    lua_pushinteger(L, BIT_TRUNCATE((lua_Integer)TOBIT(L, 1, f) op      \
                                    (unsigned)luaL_checknumber(L, 2))); \
    return 1;                                                           \
  }

MONADIC(cast,  +)
MONADIC(bnot,  ~)
VARIADIC(band, &=)
VARIADIC(bor,  |=)
VARIADIC(bxor, ^=)
ARITHMETIC_SHIFT(lshift,  <<)
LOGICAL_SHIFT(rshift,     >>)
ARITHMETIC_SHIFT(arshift, >>)

static const struct luaL_reg bitlib[] = {
  {"cast",    bit_cast},
  {"bnot",    bit_bnot},
  {"band",    bit_band},
  {"bor",     bit_bor},
  {"bxor",    bit_bxor},
  {"lshift",  bit_lshift},
  {"rshift",  bit_rshift},
  {"arshift", bit_arshift},
  {NULL, NULL}
};

LUALIB_API int luaopen_bit (lua_State *L) {
  luaL_register(L, "bit", bitlib);
  lua_pushnumber(L, BIT_BITS);
  lua_setfield(L, -2, "bits");
  return 1;
}