diff options
Diffstat (limited to 'util-src/strbitop.c')
| -rw-r--r-- | util-src/strbitop.c | 37 |
1 files changed, 37 insertions, 0 deletions
diff --git a/util-src/strbitop.c b/util-src/strbitop.c index 75cfea81..2f6bf6e6 100644 --- a/util-src/strbitop.c +++ b/util-src/strbitop.c @@ -8,6 +8,8 @@ #include <lua.h> #include <lauxlib.h> +#include <sys/param.h> +#include <limits.h> /* TODO Deduplicate code somehow */ @@ -74,11 +76,46 @@ static int strop_xor(lua_State *L) { 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 } }; |