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/*
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bdiff.c - efficient binary diff extension for Mercurial
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Copyright 2005, 2006 Matt Mackall <mpm@selenic.com>
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This software may be used and distributed according to the terms of
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the GNU General Public License, incorporated herein by reference.
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Based roughly on Python difflib
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*/
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#include <limits.h>
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#include <stdlib.h>
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#include <string.h>
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#include "bdiff.h"
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#include "bitmanipulation.h"
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#include "compat.h"
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/* Hash implementation from diffutils */
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#define ROL(v, n) ((v) << (n) | (v) >> (sizeof(v) * CHAR_BIT - (n)))
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#define HASH(h, c) ((c) + ROL(h ,7))
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struct pos {
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int pos, len;
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};
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int bdiff_splitlines(const char *a, ssize_t len, struct bdiff_line **lr)
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{
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unsigned hash;
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int i;
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const char *p, *b = a;
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const char * const plast = a + len - 1;
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struct bdiff_line *l;
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/* count the lines */
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i = 1; /* extra line for sentinel */
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for (p = a; p < plast; p++)
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if (*p == '\n')
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i++;
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if (p == plast)
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i++;
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*lr = l = (struct bdiff_line *)malloc(sizeof(struct bdiff_line) * i);
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if (!l)
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return -1;
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/* build the line array and calculate hashes */
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hash = 0;
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for (p = a; p < plast; p++) {
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hash = HASH(hash, *p);
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if (*p == '\n') {
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l->hash = hash;
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hash = 0;
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l->len = p - b + 1;
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l->l = b;
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l->n = INT_MAX;
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l++;
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b = p + 1;
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}
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}
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if (p == plast) {
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hash = HASH(hash, *p);
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l->hash = hash;
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l->len = p - b + 1;
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l->l = b;
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l->n = INT_MAX;
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l++;
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}
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/* set up a sentinel */
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l->hash = 0;
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l->len = 0;
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l->l = a + len;
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return i - 1;
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}
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static inline int cmp(struct bdiff_line *a, struct bdiff_line *b)
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{
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return a->hash != b->hash || a->len != b->len || memcmp(a->l, b->l, a->len);
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}
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static int equatelines(struct bdiff_line *a, int an, struct bdiff_line *b,
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int bn)
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{
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int i, j, buckets = 1, t, scale;
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struct pos *h = NULL;
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/* build a hash table of the next highest power of 2 */
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while (buckets < bn + 1)
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buckets *= 2;
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/* try to allocate a large hash table to avoid collisions */
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for (scale = 4; scale; scale /= 2) {
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h = (struct pos *)malloc(scale * buckets * sizeof(struct pos));
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if (h)
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break;
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}
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if (!h)
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return 0;
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buckets = buckets * scale - 1;
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/* clear the hash table */
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for (i = 0; i <= buckets; i++) {
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h[i].pos = -1;
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h[i].len = 0;
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}
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/* add lines to the hash table chains */
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for (i = 0; i < bn; i++) {
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/* find the equivalence class */
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for (j = b[i].hash & buckets; h[j].pos != -1;
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j = (j + 1) & buckets)
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if (!cmp(b + i, b + h[j].pos))
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break;
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/* add to the head of the equivalence class */
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b[i].n = h[j].pos;
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b[i].e = j;
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h[j].pos = i;
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h[j].len++; /* keep track of popularity */
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}
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/* compute popularity threshold */
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t = (bn >= 31000) ? bn / 1000 : 1000000 / (bn + 1);
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/* match items in a to their equivalence class in b */
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for (i = 0; i < an; i++) {
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/* find the equivalence class */
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for (j = a[i].hash & buckets; h[j].pos != -1;
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j = (j + 1) & buckets)
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if (!cmp(a + i, b + h[j].pos))
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break;
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a[i].e = j; /* use equivalence class for quick compare */
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if (h[j].len <= t)
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a[i].n = h[j].pos; /* point to head of match list */
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else
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a[i].n = -1; /* too popular */
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}
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/* discard hash tables */
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free(h);
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return 1;
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}
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static int longest_match(struct bdiff_line *a, struct bdiff_line *b,
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struct pos *pos,
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int a1, int a2, int b1, int b2, int *omi, int *omj)
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{
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int mi = a1, mj = b1, mk = 0, i, j, k, half, bhalf;
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/* window our search on large regions to better bound
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worst-case performance. by choosing a window at the end, we
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reduce skipping overhead on the b chains. */
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if (a2 - a1 > 30000)
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a1 = a2 - 30000;
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half = (a1 + a2 - 1) / 2;
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bhalf = (b1 + b2 - 1) / 2;
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for (i = a1; i < a2; i++) {
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/* skip all lines in b after the current block */
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for (j = a[i].n; j >= b2; j = b[j].n)
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;
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/* loop through all lines match a[i] in b */
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for (; j >= b1; j = b[j].n) {
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/* does this extend an earlier match? */
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for (k = 1; j - k >= b1 && i - k >= a1; k++) {
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/* reached an earlier match? */
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if (pos[j - k].pos == i - k) {
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k += pos[j - k].len;
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break;
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}
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/* previous line mismatch? */
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if (a[i - k].e != b[j - k].e)
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break;
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}
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pos[j].pos = i;
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pos[j].len = k;
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/* best match so far? we prefer matches closer
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to the middle to balance recursion */
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if (k > mk) {
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/* a longer match */
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mi = i;
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mj = j;
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mk = k;
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} else if (k == mk) {
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if (i > mi && i <= half && j > b1) {
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/* same match but closer to half */
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mi = i;
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mj = j;
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} else if (i == mi && (mj > bhalf || i == a1)) {
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/* same i but best earlier j */
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mj = j;
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}
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}
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}
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}
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if (mk) {
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mi = mi - mk + 1;
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mj = mj - mk + 1;
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}
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/* expand match to include subsequent popular lines */
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while (mi + mk < a2 && mj + mk < b2 &&
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a[mi + mk].e == b[mj + mk].e)
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mk++;
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*omi = mi;
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*omj = mj;
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return mk;
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}
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static struct bdiff_hunk *recurse(struct bdiff_line *a, struct bdiff_line *b,
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struct pos *pos,
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int a1, int a2, int b1, int b2, struct bdiff_hunk *l)
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{
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int i, j, k;
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while (1) {
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/* find the longest match in this chunk */
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k = longest_match(a, b, pos, a1, a2, b1, b2, &i, &j);
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if (!k)
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return l;
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/* and recurse on the remaining chunks on either side */
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l = recurse(a, b, pos, a1, i, b1, j, l);
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if (!l)
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return NULL;
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l->next = (struct bdiff_hunk *)malloc(sizeof(struct bdiff_hunk));
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if (!l->next)
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return NULL;
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l = l->next;
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l->a1 = i;
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l->a2 = i + k;
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l->b1 = j;
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l->b2 = j + k;
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l->next = NULL;
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/* tail-recursion didn't happen, so do equivalent iteration */
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a1 = i + k;
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b1 = j + k;
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}
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}
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int bdiff_diff(struct bdiff_line *a, int an, struct bdiff_line *b,
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int bn, struct bdiff_hunk *base)
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{
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struct bdiff_hunk *curr;
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struct pos *pos;
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int t, count = 0;
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/* allocate and fill arrays */
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t = equatelines(a, an, b, bn);
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pos = (struct pos *)calloc(bn ? bn : 1, sizeof(struct pos));
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if (pos && t) {
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/* generate the matching block list */
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curr = recurse(a, b, pos, 0, an, 0, bn, base);
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if (!curr)
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return -1;
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/* sentinel end hunk */
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curr->next = (struct bdiff_hunk *)malloc(sizeof(struct bdiff_hunk));
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if (!curr->next)
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return -1;
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curr = curr->next;
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curr->a1 = curr->a2 = an;
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curr->b1 = curr->b2 = bn;
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curr->next = NULL;
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}
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free(pos);
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/* normalize the hunk list, try to push each hunk towards the end */
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for (curr = base->next; curr; curr = curr->next) {
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struct bdiff_hunk *next = curr->next;
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if (!next)
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break;
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if (curr->a2 == next->a1 || curr->b2 == next->b1)
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while (curr->a2 < an && curr->b2 < bn
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&& next->a1 < next->a2
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&& next->b1 < next->b2
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&& !cmp(a + curr->a2, b + curr->b2)) {
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curr->a2++;
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next->a1++;
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curr->b2++;
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next->b1++;
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}
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}
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for (curr = base->next; curr; curr = curr->next)
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count++;
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return count;
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}
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void bdiff_freehunks(struct bdiff_hunk *l)
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{
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struct bdiff_hunk *n;
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for (; l; l = n) {
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n = l->next;
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free(l);
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}
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}
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