/*

 * This project is MIT licensed. Please see the

 * COPYING file in the source package for more information.

 *

 * Copyright (C) 2016 Kim Alvefur

 */

#include <lua.h>

#include <lauxlib.h>

#include <sys/param.h>

#include <limits.h>

/* TODO Deduplicate code somehow */

static int strop_and(lua_State *L) {

	luaL_Buffer buf;

	size_t a, b, i;

	const char *str_a = luaL_checklstring(L, 1, &a);

	const char *str_b = luaL_checklstring(L, 2, &b);

	luaL_buffinit(L, &buf);

	if(a == 0 || b == 0) {

		lua_settop(L, 1);

		return 1;

	}

	for(i = 0; i < a; i++) {

		luaL_addchar(&buf, str_a[i] & str_b[i % b]);

	}

	luaL_pushresult(&buf);

	return 1;

}

static int strop_or(lua_State *L) {

	luaL_Buffer buf;

	size_t a, b, i;

	const char *str_a = luaL_checklstring(L, 1, &a);

	const char *str_b = luaL_checklstring(L, 2, &b);

	luaL_buffinit(L, &buf);

	if(a == 0 || b == 0) {

		lua_settop(L, 1);

		return 1;

	}

	for(i = 0; i < a; i++) {

		luaL_addchar(&buf, str_a[i] | str_b[i % b]);

	}

	luaL_pushresult(&buf);

	return 1;

}

static int strop_xor(lua_State *L) {

	luaL_Buffer buf;

	size_t a, b, i;

	const char *str_a = luaL_checklstring(L, 1, &a);

	const char *str_b = luaL_checklstring(L, 2, &b);

	luaL_buffinit(L, &buf);

	if(a == 0 || b == 0) {

		lua_settop(L, 1);

		return 1;

	}

	for(i = 0; i < a; i++) {

		luaL_addchar(&buf, str_a[i] ^ str_b[i % b]);

	}

	luaL_pushresult(&buf);

	return 1;

}

unsigned int clz(unsigned char c) {

#if __GNUC__

	return __builtin_clz((unsigned int) c) - ((sizeof(int)-1)*CHAR_BIT);

#else

	if(c & 0x80) return 0;

	if(c & 0x40) return 1;

	if(c & 0x20) return 2;

	if(c & 0x10) return 3;

	if(c & 0x08) return 4;

	if(c & 0x04) return 5;

	if(c & 0x02) return 6;

	if(c & 0x01) return 7;

	return 8;

#endif

}

LUA_API int strop_common_prefix_bits(lua_State *L) {

	size_t a, b, i;

	const char *str_a = luaL_checklstring(L, 1, &a);

	const char *str_b = luaL_checklstring(L, 2, &b);

	size_t min_len = MIN(a, b);

	for(i=0; i<min_len; i++) {

		if(str_a[i] != str_b[i]) {

			lua_pushinteger(L, i*8 + (clz(str_a[i] ^ str_b[i])));

			return 1;

		}

	}

	lua_pushinteger(L, i*8);

	return 1;

}

LUA_API int luaopen_prosody_util_strbitop(lua_State *L) {

	luaL_Reg exports[] = {

		{ "sand", strop_and },

		{ "sor",  strop_or },

		{ "sxor", strop_xor },

		{ "common_prefix_bits", strop_common_prefix_bits },

		{ NULL, NULL }

	};

	lua_newtable(L);

	luaL_setfuncs(L, exports, 0);

	return 1;

}

LUA_API int luaopen_util_strbitop(lua_State *L) {

	return luaopen_prosody_util_strbitop(L);

}