diff-delta: big code simplification

This is much smaller and hopefully clearer code now.

Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>

diff --git a/diff-delta.c b/diff-delta.c
index ac992e21b878790e4cafce78feeb0a2d071578e9..2ed5984b1c360194d53fd287962d7857e19a097c 100644 (file)
--- a/diff-delta.c
+++ b/diff-delta.c
@@ -19,8 +19,9 @@
  */
 
 #include <stdlib.h>
+#include <string.h>
+#include <zlib.h>
 #include "delta.h"
-#include "zlib.h"
 
 
 /* block size: min = 16, max = 64k, power of 2 */
@@ -29,123 +30,54 @@
 #define MIN(a, b) ((a) < (b) ? (a) : (b))
 
 #define GR_PRIME 0x9e370001
-#define HASH(v, b) (((unsigned int)(v) * GR_PRIME) >> (32 - (b)))
-       
-static unsigned int hashbits(unsigned int size)
-{
-       unsigned int val = 1, bits = 0;
-       while (val < size && bits < 32) {
-               val <<= 1;
-               bits++;
-       }
-       return bits ? bits: 1;
-}
-
-typedef struct s_chanode {
-       struct s_chanode *next;
-       int icurr;
-} chanode_t;
-
-typedef struct s_chastore {
-       int isize, nsize;
-       chanode_t *ancur;
-} chastore_t;
-
-static void cha_init(chastore_t *cha, int isize, int icount)
-{
-       cha->isize = isize;
-       cha->nsize = icount * isize;
-       cha->ancur = NULL;
-}
-
-static void *cha_alloc(chastore_t *cha)
-{
-       chanode_t *ancur;
-       void *data;
-
-       ancur = cha->ancur;
-       if (!ancur || ancur->icurr == cha->nsize) {
-               ancur = malloc(sizeof(chanode_t) + cha->nsize);
-               if (!ancur)
-                       return NULL;
-               ancur->icurr = 0;
-               ancur->next = cha->ancur;
-               cha->ancur = ancur;
-       }
-
-       data = (void *)ancur + sizeof(chanode_t) + ancur->icurr;
-       ancur->icurr += cha->isize;
-       return data;
-}
-
-static void cha_free(chastore_t *cha)
-{
-       chanode_t *cur = cha->ancur;
-       while (cur) {
-               chanode_t *tmp = cur;
-               cur = cur->next;
-               free(tmp);
-       }
-}
+#define HASH(v, shift) (((unsigned int)(v) * GR_PRIME) >> (shift))
 
-typedef struct s_bdrecord {
-       struct s_bdrecord *next;
-       unsigned int fp;
+struct index {
        const unsigned char *ptr;
-} bdrecord_t;
+       unsigned int val;
+       struct index *next;
+};
 
-typedef struct s_bdfile {
-       chastore_t cha;
-       unsigned int fphbits;
-       bdrecord_t **fphash;
-} bdfile_t;
-
-static int delta_prepare(const unsigned char *buf, int bufsize, bdfile_t *bdf)
+static struct index ** delta_index(const unsigned char *buf,
+                                  unsigned long bufsize,
+                                  unsigned int *hash_shift)
 {
-       unsigned int fphbits;
-       int i, hsize;
-       const unsigned char *data, *top;
-       bdrecord_t *brec;
-       bdrecord_t **fphash;
-
-       fphbits = hashbits(bufsize / BLK_SIZE + 1);
-       hsize = 1 << fphbits;
-       fphash = malloc(hsize * sizeof(bdrecord_t *));
-       if (!fphash)
-               return -1;
-       for (i = 0; i < hsize; i++)
-               fphash[i] = NULL;
-       cha_init(&bdf->cha, sizeof(bdrecord_t), hsize / 4 + 1);
-
-       top = buf + bufsize;
-       data = buf + (bufsize / BLK_SIZE) * BLK_SIZE;
-       if (data == top)
+       unsigned int hsize, hshift, entries, blksize, 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 = 1 << i;
+       hshift = 32 - i;
+       *hash_shift = hshift;
+
+       /* allocate lookup index */
+       mem = malloc(hsize * sizeof(*hash) + entries * sizeof(*entry));
+       if (!mem)
+               return NULL;
+       hash = mem;
+       entry = mem + hsize * sizeof(*hash);
+       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;
+               entry->next = hash[i];
+               hash[i] = entry++;
+               blksize = BLK_SIZE;
                data -= BLK_SIZE;
+       }
 
-       for ( ; data >= buf; data -= BLK_SIZE) {
-               brec = cha_alloc(&bdf->cha);
-               if (!brec) {
-                       cha_free(&bdf->cha);
-                       free(fphash);
-                       return -1;
-               }
-               brec->fp = adler32(0, data, MIN(BLK_SIZE, top - data));
-               brec->ptr = data;
-               i = HASH(brec->fp, fphbits);
-               brec->next = fphash[i];
-               fphash[i] = brec;
-       }
-
-       bdf->fphbits = fphbits;
-       bdf->fphash = fphash;
-
-       return 0;
-}
-
-static void delta_cleanup(bdfile_t *bdf)
-{
-       free(bdf->fphash);
-       cha_free(&bdf->cha);
+       return hash;
 }
 
 /* provide the size of the copy opcode given the block offset and size */
@@ -161,23 +93,24 @@ void *diff_delta(void *from_buf, unsigned long from_size,
                 unsigned long *delta_size,
                 unsigned long max_size)
 {
-       unsigned int i, outpos, outsize, inscnt, csize, msize, moff;
-       unsigned int fp;
-       const unsigned char *ref_data, *ref_top, *data, *top, *ptr1, *ptr2;
-       unsigned char *out, *orig;
-       bdrecord_t *brec;
-       bdfile_t bdf;
+       unsigned int i, outpos, outsize, inscnt, hash_shift;
+       const unsigned char *ref_data, *ref_top, *data, *top;
+       unsigned char *out;
+       struct index *entry, **hash;
 
-       if (!from_size || !to_size || delta_prepare(from_buf, from_size, &bdf))
+       if (!from_size || !to_size)
                return NULL;
-       
+       hash = delta_index(from_buf, from_size, &hash_shift);
+       if (!hash)
+               return NULL;
+
        outpos = 0;
        outsize = 8192;
        if (max_size && outsize >= max_size)
                outsize = max_size + MAX_OP_SIZE + 1;
        out = malloc(outsize);
        if (!out) {
-               delta_cleanup(&bdf);
+               free(hash);
                return NULL;
        }
 
@@ -205,28 +138,32 @@ void *diff_delta(void *from_buf, unsigned long from_size,
        }
 
        inscnt = 0;
-       moff = 0;
-       while (data < top) {
-               msize = 0;
-               fp = adler32(0, data, MIN(top - data, BLK_SIZE));
-               i = HASH(fp, bdf.fphbits);
-               for (brec = bdf.fphash[i]; brec; brec = brec->next) {
-                       if (brec->fp == fp) {
-                               csize = ref_top - brec->ptr;
-                               if (csize > top - data)
-                                       csize = top - data;
-                               for (ptr1 = brec->ptr, ptr2 = data; 
-                                    csize && *ptr1 == *ptr2;
-                                    csize--, ptr1++, ptr2++);
 
-                               csize = ptr1 - brec->ptr;
-                               if (csize > msize) {
-                                       moff = brec->ptr - ref_data;
-                                       msize = csize;
-                                       if (msize >= 0x10000) {
-                                               msize = 0x10000;
-                                               break;
-                                       }
+       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;
+                                       break;
                                }
                        }
                }
@@ -241,13 +178,15 @@ void *diff_delta(void *from_buf, unsigned long from_size,
                                inscnt = 0;
                        }
                } else {
+                       unsigned char *op;
+
                        if (inscnt) {
                                out[outpos - inscnt - 1] = inscnt;
                                inscnt = 0;
                        }
 
                        data += msize;
-                       orig = out + outpos++;
+                       op = out + outpos++;
                        i = 0x80;
 
                        if (moff & 0xff) { out[outpos++] = moff; i |= 0x01; }
@@ -262,7 +201,7 @@ void *diff_delta(void *from_buf, unsigned long from_size,
                        msize >>= 8;
                        if (msize & 0xff) { out[outpos++] = msize; i |= 0x20; }
 
-                       *orig = i;
+                       *op = i;
                }
 
                if (outpos >= outsize - MAX_OP_SIZE) {
@@ -276,7 +215,7 @@ void *diff_delta(void *from_buf, unsigned long from_size,
                                out = realloc(out, outsize);
                        if (!out) {
                                free(tmp);
-                               delta_cleanup(&bdf);
+                               free(hash);
                                return NULL;
                        }
                }
@@ -285,7 +224,7 @@ void *diff_delta(void *from_buf, unsigned long from_size,
        if (inscnt)
                out[outpos - inscnt - 1] = inscnt;
 
-       delta_cleanup(&bdf);
+       free(hash);
        *delta_size = outpos;
        return out;
 }