## test case
open('a','w').write(''.join('%s\n' % (i % 100000) for i in xrange(10000000)))
open('b','w').write(''.join('%s\n' % (i % 100000) for i in xrange(10000001)))

## before xxhash
./xdiff /tmp/[ab] &> /dev/null  0.67s user 0.21s system 99% cpu 0.875 total
## after xxhash
./xdiff /tmp/[ab] &> /dev/null  2.86s user 0.43s system 98% cpu 3.315 total

// contrib/xdiff/xdiff.c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#include "mercurial/thirdparty/xdiff/xdiff.h"

#define abort(...)                                                             \
	{                                                                      \
		fprintf(stderr, __VA_ARGS__);                                  \
		exit(-1);                                                      \
	}

char buf[4096000];
void readfile(const char *path, mmfile_t *file)
{
	memset(file, 0, sizeof(*file));
	FILE *fp = fopen(path, "r");
	if (!fp) {
		abort("cannot open %s\n", path);
	}
	while (!feof(fp)) {
		size_t size = fread(buf, 1, sizeof buf, fp);
		if (size > 0) {
			size_t new_size = file->size + size;
			file->ptr = realloc(file->ptr, new_size);
			if (!file->ptr) {
				abort("cannot allocate\n");
			}
			memcpy(file->ptr + file->size, buf, size);
			file->size = new_size;
		}
	}
	fclose(fp);
}

static int xdiff_outf(void *priv_, mmbuffer_t *mb, int nbuf)
{
	int i;
	for (i = 0; i < nbuf; i++) {
		write(STDOUT_FILENO, mb[i].ptr, mb[i].size);
	}
	return 0;
}

int main(int argc, char const *argv[])
{
	if (argc < 3) {
		abort("usage: %s FILE1 FILE2\n", argv[0]);
	}

	mmfile_t a, b;

	readfile(argv[1], &a);
	readfile(argv[2], &b);

	xpparam_t xpp = {
	    0,    /* flags */
	    NULL, /* anchors */
	    0,    /* anchors_nr */
	};
	xdemitconf_t xecfg = {
	    3,    /* ctxlen */
	    0,    /* interhunkctxlen */
	    0,    /* flags */
	    NULL, /* find_func */
	    NULL, /* find_func_priv */
	    NULL, /* hunk_consume_func */
	};
	xdemitcb_t ecb = {
	    0,           /* priv */
	    &xdiff_outf, /* outf */
	};

	xdl_diff(&a, &b, &xpp, &xecfg, &ecb);

	free(a.ptr);
	free(b.ptr);

	return 0;
}

## contrib/xdiff/Makefile
xdiff: ../../mercurial/thirdparty/xdiff/*.c xdiff.c
	gcc -O2 -g -std=c99 -I../.. -I../../mercurial/thirdparty/xdiff -I../../mercurial -o $@ $^

clean:
	-rm -f xdiff