mirror of
https://github.com/bjc/prosody.git
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7f748556a2
This returns the number of bits that two strings have in common. It is significantly more efficient than similar calculations in Lua.
129 lines
2.4 KiB
C
129 lines
2.4 KiB
C
/*
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* This project is MIT licensed. Please see the
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* COPYING file in the source package for more information.
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*
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* Copyright (C) 2016 Kim Alvefur
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*/
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#include <lua.h>
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#include <lauxlib.h>
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#include <sys/param.h>
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#include <limits.h>
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/* TODO Deduplicate code somehow */
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static int strop_and(lua_State *L) {
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luaL_Buffer buf;
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size_t a, b, i;
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const char *str_a = luaL_checklstring(L, 1, &a);
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const char *str_b = luaL_checklstring(L, 2, &b);
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luaL_buffinit(L, &buf);
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if(a == 0 || b == 0) {
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lua_settop(L, 1);
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return 1;
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}
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for(i = 0; i < a; i++) {
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luaL_addchar(&buf, str_a[i] & str_b[i % b]);
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}
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luaL_pushresult(&buf);
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return 1;
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}
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static int strop_or(lua_State *L) {
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luaL_Buffer buf;
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size_t a, b, i;
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const char *str_a = luaL_checklstring(L, 1, &a);
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const char *str_b = luaL_checklstring(L, 2, &b);
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luaL_buffinit(L, &buf);
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if(a == 0 || b == 0) {
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lua_settop(L, 1);
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return 1;
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}
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for(i = 0; i < a; i++) {
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luaL_addchar(&buf, str_a[i] | str_b[i % b]);
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}
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luaL_pushresult(&buf);
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return 1;
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}
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static int strop_xor(lua_State *L) {
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luaL_Buffer buf;
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size_t a, b, i;
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const char *str_a = luaL_checklstring(L, 1, &a);
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const char *str_b = luaL_checklstring(L, 2, &b);
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luaL_buffinit(L, &buf);
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if(a == 0 || b == 0) {
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lua_settop(L, 1);
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return 1;
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}
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for(i = 0; i < a; i++) {
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luaL_addchar(&buf, str_a[i] ^ str_b[i % b]);
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}
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luaL_pushresult(&buf);
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return 1;
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}
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unsigned int clz(unsigned char c) {
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#if __GNUC__
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return __builtin_clz((unsigned int) c) - ((sizeof(int)-1)*CHAR_BIT);
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#else
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if(c & 0x80) return 0;
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if(c & 0x40) return 1;
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if(c & 0x20) return 2;
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if(c & 0x10) return 3;
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if(c & 0x08) return 4;
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if(c & 0x04) return 5;
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if(c & 0x02) return 6;
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if(c & 0x01) return 7;
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return 8;
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#endif
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}
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LUA_API int strop_common_prefix_bits(lua_State *L) {
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size_t a, b, i;
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const char *str_a = luaL_checklstring(L, 1, &a);
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const char *str_b = luaL_checklstring(L, 2, &b);
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size_t min_len = MIN(a, b);
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for(i=0; i<min_len; i++) {
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if(str_a[i] != str_b[i]) {
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lua_pushinteger(L, i*8 + (clz(str_a[i] ^ str_b[i])));
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return 1;
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}
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}
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lua_pushinteger(L, i*8);
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return 1;
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}
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LUA_API int luaopen_prosody_util_strbitop(lua_State *L) {
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luaL_Reg exports[] = {
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{ "sand", strop_and },
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{ "sor", strop_or },
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{ "sxor", strop_xor },
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{ "common_prefix_bits", strop_common_prefix_bits },
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{ NULL, NULL }
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};
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lua_newtable(L);
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luaL_setfuncs(L, exports, 0);
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return 1;
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}
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LUA_API int luaopen_util_strbitop(lua_State *L) {
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return luaopen_prosody_util_strbitop(L);
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}
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