/*
bdiff.c - efficient binary diff extension for Mercurial
Copyright 2005, 2006 Matt Mackall <mpm@selenic.com>
This software may be used and distributed according to the terms of
the GNU General Public License, incorporated herein by reference.
Based roughly on Python difflib
*/
#include <Python.h>
#include <stdlib.h>
#include <string.h>
#include <limits.h>
#if defined __hpux || defined __SUNPRO_C || defined _AIX
# define inline
#endif
#ifdef _WIN32
#ifdef _MSC_VER
#define inline __inline
typedef unsigned long uint32_t;
#else
#include <stdint.h>
#endif
static uint32_t htonl(uint32_t x)
{
return ((x & 0x000000ffUL) << 24) |
((x & 0x0000ff00UL) << 8) |
((x & 0x00ff0000UL) >> 8) |
((x & 0xff000000UL) >> 24);
}
#else
#include <sys/types.h>
#ifdef __BEOS__
#include <ByteOrder.h>
#else
#include <arpa/inet.h>
#endif
#include <inttypes.h>
#endif
struct line {
int h, len, n, e;
const char *l;
};
struct pos {
int pos, len;
};
struct hunk {
int a1, a2, b1, b2;
};
struct hunklist {
struct hunk *base, *head;
};
static inline uint32_t rol32(uint32_t word, unsigned int shift)
{
return (word << shift) | (word >> (32 - shift));
}
int splitlines(const char *a, int len, struct line **lr)
{
int g, h, i;
const char *p, *b = a;
const char * const plast = a + len - 1;
struct line *l;
/* count the lines */
i = 1; /* extra line for sentinel */
for (p = a; p < a + len; p++)
if (*p == '\n' || p == plast)
i++;
*lr = l = (struct line *)malloc(sizeof(struct line) * i);
if (!l)
return -1;
/* build the line array and calculate hashes */
h = 0;
for (p = a; p < a + len; p++) {
/*
* a simple hash from GNU diff, with better collision
* resistance from hashpjw. this slows down common
* case by 10%, but speeds up worst case by 100x.
*/
h = *p + rol32(h, 7);
if ((g = h & 0xf0000000)) {
h ^= g >> 24;
h ^= g;
}
if (*p == '\n' || p == plast) {
l->len = p - b + 1;
l->h = h * l->len;
l->l = b;
l->n = INT_MAX;
l++;
b = p + 1;
h = 0;
}
}
/* set up a sentinel */
l->h = l->len = 0;
l->l = a + len;
return i - 1;
}
int inline cmp(struct line *a, struct line *b)
{
return a->h != b->h || a->len != b->len || memcmp(a->l, b->l, a->len);
}
static int equatelines(struct line *a, int an, struct line *b, int bn)
{
int i, j, buckets = 1, t;
int scale = 32;
struct pos *h;
/* build a hash table of the next highest power of 2 */
while (buckets < bn + 1)
buckets *= 2;
/* try to allocate a large hash table to avoid collisions */
do {
scale /= 2;
h = (struct pos *)malloc(scale * buckets * sizeof(struct pos));
} while (!h && scale != 1);
if (!h)
return 0;
buckets = buckets * scale - 1;
/* clear the hash table */
for (i = 0; i <= buckets; i++) {
h[i].pos = INT_MAX;
h[i].len = 0;
}
/* add lines to the hash table chains */
for (i = bn - 1; i >= 0; i--) {
/* find the equivalence class */
for (j = b[i].h & buckets; h[j].pos != INT_MAX;
j = (j + 1) & buckets)
if (!cmp(b + i, b + h[j].pos))
break;
/* add to the head of the equivalence class */
b[i].n = h[j].pos;
b[i].e = j;
h[j].pos = i;
h[j].len++; /* keep track of popularity */
}
/* compute popularity threshold */
t = (bn >= 200) ? bn / 100 : bn + 1;
/* match items in a to their equivalence class in b */
for (i = 0; i < an; i++) {
/* find the equivalence class */
for (j = a[i].h & buckets; h[j].pos != INT_MAX;
j = (j + 1) & buckets)
if (!cmp(a + i, b + h[j].pos))
break;
a[i].e = j; /* use equivalence class for quick compare */
if (h[j].len <= t)
a[i].n = h[j].pos; /* point to head of match list */
else
a[i].n = INT_MAX; /* too popular */
}
/* discard hash tables */
free(h);
return 1;
}
static int longest_match(struct line *a, struct line *b, struct pos *pos,
int a1, int a2, int b1, int b2, int *omi, int *omj)
{
int mi = a1, mj = b1, mk = 0, mb = 0, i, j, k;
for (i = a1; i < a2; i++) {
/* skip things before the current block */
for (j = a[i].n; j < b1; j = b[j].n)
;
/* loop through all lines match a[i] in b */
for (; j < b2; j = b[j].n) {
/* does this extend an earlier match? */
if (i > a1 && j > b1 && pos[j - 1].pos == i - 1)
k = pos[j - 1].len + 1;
else
k = 1;
pos[j].pos = i;
pos[j].len = k;
/* best match so far? */
if (k > mk) {
mi = i;
mj = j;
mk = k;
}
}
}
if (mk) {
mi = mi - mk + 1;
mj = mj - mk + 1;
}
/* expand match to include neighboring popular lines */
while (mi - mb > a1 && mj - mb > b1 &&
a[mi - mb - 1].e == b[mj - mb - 1].e)
mb++;
while (mi + mk < a2 && mj + mk < b2 &&
a[mi + mk].e == b[mj + mk].e)
mk++;
*omi = mi - mb;
*omj = mj - mb;
return mk + mb;
}
static void recurse(struct line *a, struct line *b, struct pos *pos,
int a1, int a2, int b1, int b2, struct hunklist *l)
{
int i, j, k;
/* find the longest match in this chunk */
k = longest_match(a, b, pos, a1, a2, b1, b2, &i, &j);
if (!k)
return;
/* and recurse on the remaining chunks on either side */
recurse(a, b, pos, a1, i, b1, j, l);
l->head->a1 = i;
l->head->a2 = i + k;
l->head->b1 = j;
l->head->b2 = j + k;
l->head++;
recurse(a, b, pos, i + k, a2, j + k, b2, l);
}
static struct hunklist diff(struct line *a, int an, struct line *b, int bn)
{
struct hunklist l;
struct pos *pos;
int t;
/* allocate and fill arrays */
t = equatelines(a, an, b, bn);
pos = (struct pos *)calloc(bn, sizeof(struct pos));
/* we can't have more matches than lines in the shorter file */
l.head = l.base = (struct hunk *)malloc(sizeof(struct hunk) *
((an<bn ? an:bn) + 1));
if (pos && l.base && t) {
/* generate the matching block list */
recurse(a, b, pos, 0, an, 0, bn, &l);
l.head->a1 = l.head->a2 = an;
l.head->b1 = l.head->b2 = bn;
l.head++;
}
free(pos);
return l;
}
static PyObject *blocks(PyObject *self, PyObject *args)
{
PyObject *sa, *sb, *rl = NULL, *m;
struct line *a, *b;
struct hunklist l = {NULL, NULL};
struct hunk *h;
int an, bn, pos = 0;
if (!PyArg_ParseTuple(args, "SS:bdiff", &sa, &sb))
return NULL;
an = splitlines(PyString_AsString(sa), PyString_Size(sa), &a);
bn = splitlines(PyString_AsString(sb), PyString_Size(sb), &b);
if (!a || !b)
goto nomem;
l = diff(a, an, b, bn);
rl = PyList_New(l.head - l.base);
if (!l.head || !rl)
goto nomem;
for (h = l.base; h != l.head; h++) {
m = Py_BuildValue("iiii", h->a1, h->a2, h->b1, h->b2);
PyList_SetItem(rl, pos, m);
pos++;
}
nomem:
free(a);
free(b);
free(l.base);
return rl ? rl : PyErr_NoMemory();
}
static PyObject *bdiff(PyObject *self, PyObject *args)
{
char *sa, *sb;
PyObject *result = NULL;
struct line *al, *bl;
struct hunklist l = {NULL, NULL};
struct hunk *h;
char encode[12], *rb;
int an, bn, len = 0, la, lb;
if (!PyArg_ParseTuple(args, "s#s#:bdiff", &sa, &la, &sb, &lb))
return NULL;
an = splitlines(sa, la, &al);
bn = splitlines(sb, lb, &bl);
if (!al || !bl)
goto nomem;
l = diff(al, an, bl, bn);
if (!l.head)
goto nomem;
/* calculate length of output */
la = lb = 0;
for (h = l.base; h != l.head; h++) {
if (h->a1 != la || h->b1 != lb)
len += 12 + bl[h->b1].l - bl[lb].l;
la = h->a2;
lb = h->b2;
}
result = PyString_FromStringAndSize(NULL, len);
if (!result)
goto nomem;
/* build binary patch */
rb = PyString_AsString(result);
la = lb = 0;
for (h = l.base; h != l.head; h++) {
if (h->a1 != la || h->b1 != lb) {
len = bl[h->b1].l - bl[lb].l;
*(uint32_t *)(encode) = htonl(al[la].l - al->l);
*(uint32_t *)(encode + 4) = htonl(al[h->a1].l - al->l);
*(uint32_t *)(encode + 8) = htonl(len);
memcpy(rb, encode, 12);
memcpy(rb + 12, bl[lb].l, len);
rb += 12 + len;
}
la = h->a2;
lb = h->b2;
}
nomem:
free(al);
free(bl);
free(l.base);
return result ? result : PyErr_NoMemory();
}
static char mdiff_doc[] = "Efficient binary diff.";
static PyMethodDef methods[] = {
{"bdiff", bdiff, METH_VARARGS, "calculate a binary diff\n"},
{"blocks", blocks, METH_VARARGS, "find a list of matching lines\n"},
{NULL, NULL}
};
PyMODINIT_FUNC initbdiff(void)
{
Py_InitModule3("bdiff", methods, mdiff_doc);
}