Fix hash function in xdiff library
Jim Mayering noticed that xdiff library took insanely long time
when comparing files with many identical lines.
This was because the hash function used in the library is broken
on 64-bit architectures and caused too many collisions.
http://thread.gmane.org/gmane.comp.version-control.git/28962/focus=28994
Acked-by: Davide Libenzi <davidel@xmaliserver.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>
diff --git a/xdiff/xmacros.h b/xdiff/xmacros.h
index 4c2fde8..e2cd202 100644
--- a/xdiff/xmacros.h
+++ b/xdiff/xmacros.h
@@ -24,14 +24,15 @@
#define XMACROS_H
-#define GR_PRIME 0x9e370001UL
#define XDL_MIN(a, b) ((a) < (b) ? (a): (b))
#define XDL_MAX(a, b) ((a) > (b) ? (a): (b))
#define XDL_ABS(v) ((v) >= 0 ? (v): -(v))
#define XDL_ISDIGIT(c) ((c) >= '0' && (c) <= '9')
-#define XDL_HASHLONG(v, b) (((unsigned long)(v) * GR_PRIME) >> ((CHAR_BIT * sizeof(unsigned long)) - (b)))
+#define XDL_ADDBITS(v,b) ((v) + ((v) >> (b)))
+#define XDL_MASKBITS(b) ((1UL << (b)) - 1)
+#define XDL_HASHLONG(v,b) (XDL_ADDBITS((unsigned long)(v), b) & XDL_MASKBITS(b))
#define XDL_PTRFREE(p) do { if (p) { xdl_free(p); (p) = NULL; } } while (0)
#define XDL_LE32_PUT(p, v) \
do { \
