From: Grigori Goronzy <greg@chown.ath.cx>
Date: Wed, 29 Jan 2014 04:25:40 +0000 (+0100)
Subject: Unroll FNV-1A hash function
X-Git-Tag: 0.11.0~16^2
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=f466b9678b4b68e56d7374dea51218348d628b06;p=libass

Unroll FNV-1A hash function

Unroll the hash function with Duff's device for improved performance.
---

diff --git a/libass/ass_utils.h b/libass/ass_utils.h
index 6d795f0..4e2ba6c 100644
--- a/libass/ass_utils.h
+++ b/libass/ass_utils.h
@@ -132,11 +132,16 @@ static inline int rot_key(double a)
 static inline unsigned fnv_32a_buf(void *buf, size_t len, unsigned hval)
 {
     unsigned char *bp = buf;
-    unsigned char *be = bp + len;
-    while (bp < be) {
-        hval ^= (unsigned) *bp++;
-        hval *= FNV1_32A_PRIME;
+    size_t n = (len + 3) / 4;
+
+    switch (len % 4) {
+    case 0: do { hval ^= (unsigned) *bp++; hval *= FNV1_32A_PRIME;
+    case 3:      hval ^= (unsigned) *bp++; hval *= FNV1_32A_PRIME;
+    case 2:      hval ^= (unsigned) *bp++; hval *= FNV1_32A_PRIME;
+    case 1:      hval ^= (unsigned) *bp++; hval *= FNV1_32A_PRIME;
+               } while (--n > 0);
     }
+
     return hval;
 }
 static inline unsigned fnv_32a_str(char *str, unsigned hval)