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Switch to fast string hash.

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This commit is contained in:
Mike Pall
2010-07-21 22:53:27 +02:00
parent d05873ee0a
commit 420124372b
4 changed files with 25 additions and 7 deletions
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26
src/lj_str.c
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@@ -76,15 +76,29 @@ GCstr *lj_str_new(lua_State *L, const char *str, size_t lenx)
GCstr *s;
GCobj *o;
MSize len = (MSize)lenx;
MSize h = len;
MSize step = (len>>5)+1; /* Partial hash. */
MSize l1;
MSize a, b, h = len;
if (lenx >= LJ_MAX_STR)
lj_err_msg(L, LJ_ERR_STROV);
for (l1 = len; l1 >= step; l1 -= step) /* Compute string hash. */
h = h ^ ((h<<5)+(h>>2)+cast(unsigned char, str[l1-1]));
/* Check if the string has already been interned. */
g = G(L);
/* Compute string hash. Constants taken from lookup3 hash by Bob Jenkins. */
if (len >= 4) { /* Caveat: unaligned access! */
a = *(const uint32_t *)str;
h ^= *(const uint32_t *)(str+len-4);
b = *(const uint32_t *)(str+(len>>1)-2);
h ^= b; h -= lj_rol(b, 14);
b += *(const uint32_t *)(str+(len>>2)-1);
} else if (len > 0) {
a = *(const uint8_t *)str;
h ^= *(const uint8_t *)(str+len-1);
b = *(const uint8_t *)(str+(len>>1));
h ^= b; h -= lj_rol(b, 14);
} else {
return &g->strempty;
}
a ^= h; a -= lj_rol(h, 11);
b ^= a; b -= lj_rol(a, 25);
h ^= b; h -= lj_rol(b, 16);
/* Check if the string has already been interned. */
for (o = gcref(g->strhash[h & g->strmask]); o != NULL; o = gcnext(o)) {
GCstr *tso = gco2str(o);
if (tso->len == len && (memcmp(str, strdata(tso), len) == 0)) {