Subject: [PATCH 3/4] xdiff: use stronger hash function internally

From: Stefan Beller <[email-masked]>
Date: Tue, 24 Oct 2017 11:59:16 -0700

Instead of using the hash seeded with 5381, and updated via
`(hash << 5) ^ new_byte`, use the FNV-1 primitives as offered by
hashmap.h, which is seeded with 0x811c9dc5 and computed as
`(hash * 0x01000193) ^ new_byte`.

Signed-off-by: Stefan Beller <[email-masked]>
---
 xdiff/xutils.c | 19 ++++++++-----------
 1 file changed, 8 insertions(+), 11 deletions(-)

diff --git a/xdiff/xutils.c b/xdiff/xutils.c
index 04d7b32e4e..a58a28c687 100644
--- a/xdiff/xutils.c
+++ b/xdiff/xutils.c
@@ -24,7 +24,8 @@
 #include <assert.h>
 #include "xinclude.h"
 
-
+#include "cache.h"
+#include "hashmap.h"

 long xdl_bogosqrt(long n) {
@@ -228,7 +229,7 @@ int xdl_recmatch(const char *l1, long s1, const char *l2, long s2, long flags)
 
 static unsigned long xdl_hash_record_with_whitespace(char const **data,
 		char const *top, long flags) {
-	unsigned long ha = 5381;
+	unsigned long ha = memhash(NULL, 0);
 	char const *ptr = *data;
 
 	for (; ptr < top && *ptr != '\n'; ptr++) {
@@ -243,21 +244,18 @@ static unsigned long xdl_hash_record_with_whitespace(char const **data,
 				; /* already handled */
 			else if (flags & XDF_IGNORE_WHITESPACE_CHANGE
 				 && !at_eol) {
-				ha += (ha << 5);
-				ha ^= (unsigned long) ' ';
+				ha = memhash_feed(ha, (unsigned char) ' ');
 			}
 			else if (flags & XDF_IGNORE_WHITESPACE_AT_EOL
 				 && !at_eol) {
 				while (ptr2 != ptr + 1) {
-					ha += (ha << 5);
-					ha ^= (unsigned long) *ptr2;
+					ha = memhash_feed(ha, (unsigned char) *ptr2);
 					ptr2++;
 				}
 			}
 			continue;
 		}
-		ha += (ha << 5);
-		ha ^= (unsigned long) *ptr;
+		ha = memhash_feed(ha, (unsigned char) *ptr);
 	}
 	*data = ptr < top ? ptr + 1: ptr;
 
@@ -265,15 +263,14 @@ static unsigned long xdl_hash_record_with_whitespace(char const **data,
 }
 
 unsigned long xdl_hash_record(char const **data, char const *top, long flags) {
-	unsigned long ha = 5381;
+	unsigned long ha = memhash(NULL, 0);
 	char const *ptr = *data;
 
 	if (flags & XDF_WHITESPACE_FLAGS)
 		return xdl_hash_record_with_whitespace(data, top, flags);
 
 	for (; ptr < top && *ptr != '\n'; ptr++) {
-		ha += (ha << 5);
-		ha ^= (unsigned long) *ptr;
+		ha = memhash_feed(ha, (unsigned char) *ptr);
 	}
 	*data = ptr < top ? ptr + 1: ptr;
 
-- 
2.15.0.rc2.6.g953226eb5f