From bec2a69fe4c2dbb377d2742a4def7e3569b4c1d4 Mon Sep 17 00:00:00 2001 From: Junio C Hamano Date: Mon, 27 Feb 2006 21:37:56 -0800 Subject: [PATCH] Revert "Revert "diff-delta: produce optimal pack data"" --- diff-delta.c | 77 ++++++++++++++++++++-------------------------------- 1 file changed, 30 insertions(+), 47 deletions(-) diff --git a/diff-delta.c b/diff-delta.c index 2ed5984b1c..27f83a0858 100644 --- a/diff-delta.c +++ b/diff-delta.c @@ -20,21 +20,11 @@ #include #include -#include #include "delta.h" -/* block size: min = 16, max = 64k, power of 2 */ -#define BLK_SIZE 16 - -#define MIN(a, b) ((a) < (b) ? (a) : (b)) - -#define GR_PRIME 0x9e370001 -#define HASH(v, shift) (((unsigned int)(v) * GR_PRIME) >> (shift)) - struct index { const unsigned char *ptr; - unsigned int val; struct index *next; }; @@ -42,21 +32,21 @@ static struct index ** delta_index(const unsigned char *buf, unsigned long bufsize, unsigned int *hash_shift) { - unsigned int hsize, hshift, entries, blksize, i; + unsigned long hsize; + unsigned int hshift, i; const unsigned char *data; struct index *entry, **hash; void *mem; /* determine index hash size */ - entries = (bufsize + BLK_SIZE - 1) / BLK_SIZE; - hsize = entries / 4; - for (i = 4; (1 << i) < hsize && i < 16; i++); + hsize = bufsize / 4; + for (i = 8; (1 << i) < hsize && i < 16; i++); hsize = 1 << i; - hshift = 32 - i; + hshift = i - 8; *hash_shift = hshift; /* allocate lookup index */ - mem = malloc(hsize * sizeof(*hash) + entries * sizeof(*entry)); + mem = malloc(hsize * sizeof(*hash) + bufsize * sizeof(*entry)); if (!mem) return NULL; hash = mem; @@ -64,17 +54,12 @@ static struct index ** delta_index(const unsigned char *buf, memset(hash, 0, hsize * sizeof(*hash)); /* then populate it */ - data = buf + entries * BLK_SIZE - BLK_SIZE; - blksize = bufsize - (data - buf); - while (data >= buf) { - unsigned int val = adler32(0, data, blksize); - i = HASH(val, hshift); - entry->ptr = data; - entry->val = val; + data = buf + bufsize - 2; + while (data > buf) { + entry->ptr = --data; + i = data[0] ^ data[1] ^ (data[2] << hshift); entry->next = hash[i]; hash[i] = entry++; - blksize = BLK_SIZE; - data -= BLK_SIZE; } return hash; @@ -141,29 +126,27 @@ void *diff_delta(void *from_buf, unsigned long from_size, while (data < top) { unsigned int moff = 0, msize = 0; - unsigned int blksize = MIN(top - data, BLK_SIZE); - unsigned int val = adler32(0, data, blksize); - i = HASH(val, hash_shift); - for (entry = hash[i]; entry; entry = entry->next) { - const unsigned char *ref = entry->ptr; - const unsigned char *src = data; - unsigned int ref_size = ref_top - ref; - if (entry->val != val) - continue; - if (ref_size > top - src) - ref_size = top - src; - while (ref_size && *src++ == *ref) { - ref++; - ref_size--; - } - ref_size = ref - entry->ptr; - if (ref_size > msize) { - /* this is our best match so far */ - moff = entry->ptr - ref_data; - msize = ref_size; - if (msize >= 0x10000) { - msize = 0x10000; + if (data + 2 < top) { + i = data[0] ^ data[1] ^ (data[2] << hash_shift); + for (entry = hash[i]; entry; entry = entry->next) { + const unsigned char *ref = entry->ptr; + const unsigned char *src = data; + unsigned int ref_size = ref_top - ref; + if (ref_size > top - src) + ref_size = top - src; + if (ref_size > 0x10000) + ref_size = 0x10000; + if (ref_size <= msize) break; + while (ref_size && *src++ == *ref) { + ref++; + ref_size--; + } + ref_size = ref - entry->ptr; + if (msize < ref - entry->ptr) { + /* this is our best match so far */ + msize = ref - entry->ptr; + moff = entry->ptr - ref_data; } } } -- 2.47.1