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authorMatthew Wild <mwild1@gmail.com>2024-02-23 12:08:37 +0000
committerMatthew Wild <mwild1@gmail.com>2024-02-23 12:08:37 +0000
commit7f748556a2e4bc189bc994707138d129af2100a4 (patch)
tree2995372728f2a34844c2026a46faf78ce5851ee1 /util-src
parent1606675762e0ac0d9609d6d5b1d69492d2e29abb (diff)
downloadprosody-7f748556a2e4bc189bc994707138d129af2100a4.tar.gz
prosody-7f748556a2e4bc189bc994707138d129af2100a4.zip
util.strbitop: Add common_prefix_bits() method
This returns the number of bits that two strings have in common. It is significantly more efficient than similar calculations in Lua.
Diffstat (limited to 'util-src')
-rw-r--r--util-src/strbitop.c37
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 }
};