From 9de0834663f28bee9e6b2c4647ed6128241ed26f Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Mon, 16 Oct 2006 19:58:54 -0700 Subject: [PATCH] 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 Signed-off-by: Junio C Hamano --- xdiff/xmacros.h | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/xdiff/xmacros.h b/xdiff/xmacros.h index 4c2fde80c1..e2cd2023b3 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 { \