/*
** $Id: lbitlib.c,v 1.18.1.2 2013/07/09 18:01:41 roberto Exp $
** Standard library for bitwise operations
** See Copyright Notice in lua.h
*/

#define lbitlib_c
#define LUA_LIB

#include "lua.h"

#include "lauxlib.h"
#include "lualib.h"

/* number of bits to consider in a number */
#if !defined(LUA_NBITS)
#define LUA_NBITS 32
#endif

#define ALLONES (~(((~(lua_Unsigned)0) << (LUA_NBITS - 1)) << 1))

/* macro to trim extra bits */
#define trim(x) ((x)&ALLONES)

/* builds a number with 'n' ones (1 <= n <= LUA_NBITS) */
#define mask(n) (~((ALLONES << 1) << ((n)-1)))

typedef lua_Unsigned b_uint;

static b_uint andaux(lua_State *L)
{
	int i, n = lua_gettop(L);
	b_uint r = ~(b_uint)0;
	for (i = 1; i <= n; i++)
		r &= luaL_checkunsigned(L, i);
	return trim(r);
}

static int b_and(lua_State *L)
{
	b_uint r = andaux(L);
	lua_pushunsigned(L, r);
	return 1;
}

static int b_test(lua_State *L)
{
	b_uint r = andaux(L);
	lua_pushboolean(L, r != 0);
	return 1;
}

static int b_or(lua_State *L)
{
	int i, n = lua_gettop(L);
	b_uint r = 0;
	for (i = 1; i <= n; i++)
		r |= luaL_checkunsigned(L, i);
	lua_pushunsigned(L, trim(r));
	return 1;
}

static int b_xor(lua_State *L)
{
	int i, n = lua_gettop(L);
	b_uint r = 0;
	for (i = 1; i <= n; i++)
		r ^= luaL_checkunsigned(L, i);
	lua_pushunsigned(L, trim(r));
	return 1;
}

static int b_not(lua_State *L)
{
	b_uint r = ~luaL_checkunsigned(L, 1);
	lua_pushunsigned(L, trim(r));
	return 1;
}

static int b_shift(lua_State *L, b_uint r, int i)
{
	if (i < 0)
	{ /* shift right? */
		i = -i;
		r = trim(r);
		if (i >= LUA_NBITS)
			r = 0;
		else
			r >>= i;
	}
	else
	{ /* shift left */
		if (i >= LUA_NBITS)
			r = 0;
		else
			r <<= i;
		r = trim(r);
	}
	lua_pushunsigned(L, r);
	return 1;
}

static int b_lshift(lua_State *L)
{
	return b_shift(L, luaL_checkunsigned(L, 1), luaL_checkint(L, 2));
}

static int b_rshift(lua_State *L)
{
	return b_shift(L, luaL_checkunsigned(L, 1), -luaL_checkint(L, 2));
}

static int b_arshift(lua_State *L)
{
	b_uint r = luaL_checkunsigned(L, 1);
	int i = luaL_checkint(L, 2);
	if (i < 0 || !(r & ((b_uint)1 << (LUA_NBITS - 1))))
		return b_shift(L, r, -i);
	else
	{ /* arithmetic shift for 'negative' number */
		if (i >= LUA_NBITS)
			r = ALLONES;
		else
			r = trim((r >> i) | ~(~(b_uint)0 >> i)); /* add signal bit */
		lua_pushunsigned(L, r);
		return 1;
	}
}

static int b_rot(lua_State *L, int i)
{
	b_uint r = luaL_checkunsigned(L, 1);
	i &= (LUA_NBITS - 1); /* i = i % NBITS */
	r = trim(r);
	if (i != 0) /* avoid undefined shift of LUA_NBITS when i == 0 */
		r = (r << i) | (r >> (LUA_NBITS - i));
	lua_pushunsigned(L, trim(r));
	return 1;
}

static int b_lrot(lua_State *L)
{
	return b_rot(L, luaL_checkint(L, 2));
}

static int b_rrot(lua_State *L)
{
	return b_rot(L, -luaL_checkint(L, 2));
}

/*
** get field and width arguments for field-manipulation functions,
** checking whether they are valid.
** ('luaL_error' called without 'return' to avoid later warnings about
** 'width' being used uninitialized.)
*/
static int fieldargs(lua_State *L, int farg, int *width)
{
	int f = luaL_checkint(L, farg);
	int w = luaL_optint(L, farg + 1, 1);
	luaL_argcheck(L, 0 <= f, farg, "field cannot be negative");
	luaL_argcheck(L, 0 < w, farg + 1, "width must be positive");
	if (f + w > LUA_NBITS)
		luaL_error(L, "trying to access non-existent bits");
	*width = w;
	return f;
}

static int b_extract(lua_State *L)
{
	int w;
	b_uint r = luaL_checkunsigned(L, 1);
	int f = fieldargs(L, 2, &w);
	r = (r >> f) & mask(w);
	lua_pushunsigned(L, r);
	return 1;
}

static int b_replace(lua_State *L)
{
	int w;
	b_uint r = luaL_checkunsigned(L, 1);
	b_uint v = luaL_checkunsigned(L, 2);
	int f = fieldargs(L, 3, &w);
	int m = mask(w);
	v &= m; /* erase bits outside given width */
	r = (r & ~(m << f)) | (v << f);
	lua_pushunsigned(L, r);
	return 1;
}

static const luaL_Reg bitlib[] = {
	{"arshift", b_arshift},
	{"band", b_and},
	{"bnot", b_not},
	{"bor", b_or},
	{"bxor", b_xor},
	{"btest", b_test},
	{"extract", b_extract},
	{"lrotate", b_lrot},
	{"lshift", b_lshift},
	{"replace", b_replace},
	{"rrotate", b_rrot},
	{"rshift", b_rshift},
	{NULL, NULL}};

LUAMOD_API int luaopen_bit32(lua_State *L)
{
	luaL_newlib(L, bitlib);
	return 1;
}
