/* diff - compute a shortest edit script (SES) given two sequences
* Copyright (c) 2004 Michael B. Allen <mba2000 ioplex.com>
*
* The MIT License
*
* Permission is hereby granted, free of charge, to any person obtaining a
* copy of this software and associated documentation files (the "Software"),
* to deal in the Software without restriction, including without limitation
* the rights to use, copy, modify, merge, publish, distribute, sublicense,
* and/or sell copies of the Software, and to permit persons to whom the
* Software is furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included
* in all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
* THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR
* OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
* ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
* OTHER DEALINGS IN THE SOFTWARE.
*/
/* This algorithm is basically Myers' solution to SES/LCS with
* the Hirschberg linear space refinement as described in the
* following publication:
*
* E. Myers, ``An O(ND) Difference Algorithm and Its Variations,''
* Algorithmica 1, 2 (1986), 251-266.
* http://www.cs.arizona.edu/people/gene/PAPERS/diff.ps
*
* This is the same algorithm used by GNU diff(1).
*/
#include <stdlib.h>
#include <limits.h>
#include <errno.h>
#include "mba/msgno.h"
#include "mba/diff.h"
#define FV(k) _v(ctx, (k), 0)
#define RV(k) _v(ctx, (k), 1)
struct _ctx {
idx_fn idx;
cmp_fn cmp;
void *context;
struct varray *buf;
struct varray *ses;
int si;
int dmax;
};
struct middle_snake {
int x, y, u, v;
};
static void
_setv(struct _ctx *ctx, int k, int r, int val)
{
int j;
int *i;
/* Pack -N to N into 0 to N * 2
*/
j = k <= 0 ? -k * 4 + r : k * 4 + (r - 2);
i = (int *)varray_get(ctx->buf, j);
*i = val;
}
static int
_v(struct _ctx *ctx, int k, int r)
{
int j;
j = k <= 0 ? -k * 4 + r : k * 4 + (r - 2);
return *((int *)varray_get(ctx->buf, j));
}
static int
_find_middle_snake(const void *a, int aoff, int n,
const void *b, int boff, int m,
struct _ctx *ctx,
struct middle_snake *ms)
{
int delta, odd, mid, d;
delta = n - m;
odd = delta & 1;
mid = (n + m) / 2;
mid += odd;
_setv(ctx, 1, 0, 0);
_setv(ctx, delta - 1, 1, n);
for (d = 0; d <= mid; d++) {
int k, x, y;
if ((2 * d - 1) >= ctx->dmax) {
return ctx->dmax;
}
for (k = d; k >= -d; k -= 2) {
if (k == -d || (k != d && FV(k - 1) < FV(k + 1))) {
x = FV(k + 1);
} else {
x = FV(k - 1) + 1;
}
y = x - k;
ms->x = x;
ms->y = y;
if (ctx->cmp) {
while (x < n && y < m && ctx->cmp(ctx->idx(a, aoff + x, ctx->context),
ctx->idx(b, boff + y, ctx->context), ctx->context) == 0) {
x++; y++;
}
} else {
const unsigned char *a0 = (const unsigned char *)a + aoff;
const unsigned char *b0 = (const unsigned char *)b + boff;
while (x < n && y < m && a0[x] == b0[y]) {
x++; y++;
}
}
_setv(ctx, k, 0, x);
if (odd && k >= (delta - (d - 1)) && k <= (delta + (d - 1))) {
if (x >= RV(k)) {
ms->u = x;
ms->v = y;
return 2 * d - 1;
}
}
}
for (k = d; k >= -d; k -= 2) {
int kr = (n - m) + k;
if (k == d || (k != -d && RV(kr - 1) < RV(kr + 1))) {
x = RV(kr - 1);
} else {
x = RV(kr + 1) - 1;
}
y = x - kr;
ms->u = x;
ms->v = y;
if (ctx->cmp) {
while (x > 0 && y > 0 && ctx->cmp(ctx->idx(a, aoff + (x - 1), ctx->context),
ctx->idx(b, boff + (y - 1), ctx->context), ctx->context) == 0) {
x--; y--;
}
} else {
const unsigned char *a0 = (const unsigned char *)a + aoff;
const unsigned char *b0 = (const unsigned char *)b + boff;
while (x > 0 && y > 0 && a0[x - 1] == b0[y - 1]) {
x--; y--;
}
}
_setv(ctx, kr, 1, x);
if (!odd && kr >= -d && kr <= d) {
if (x <= FV(kr)) {
ms->x = x;
ms->y = y;
return 2 * d;
}
}
}
}
errno = EFAULT;
return -1;
}
static void
_edit(struct _ctx *ctx, int op, int off, int len)
{
struct diff_edit *e;
if (len == 0 || ctx->ses == NULL) {
return;
} /* Add an edit to the SES (or
* coalesce if the op is the same)
*/
e = varray_get(ctx->ses, ctx->si);
if (e->op != op) {
if (e->op) {
ctx->si++;
e = varray_get(ctx->ses, ctx->si);
}
e->op = op;
e->off = off;
e->len = len;
} else {
e->len += len;
}
}
static int
_ses(const void *a, int aoff, int n,
const void *b, int boff, int m,
struct _ctx *ctx)
{
struct middle_snake ms;
int d;
if (n == 0) {
_edit(ctx, DIFF_INSERT, boff, m);
d = m;
} else if (m == 0) {
_edit(ctx, DIFF_DELETE, aoff, n);
d = n;
} else {
/* Find the middle "snake" around which we
* recursively solve the sub-problems.
*/
d = _find_middle_snake(a, aoff, n, b, boff, m, ctx, &ms);
if (d == -1) {
return -1;
} else if (d >= ctx->dmax) {
return ctx->dmax;
} else if (ctx->ses == NULL) {
return d;
} else if (d > 1) {
if (_ses(a, aoff, ms.x, b, boff, ms.y, ctx) == -1) {
return -1;
}
_edit(ctx, DIFF_MATCH, aoff + ms.x, ms.u - ms.x);
aoff += ms.u;
boff += ms.v;
n -= ms.u;
m -= ms.v;
if (_ses(a, aoff, n, b, boff, m, ctx) == -1) {
return -1;
}
} else {
int x = ms.x;
int u = ms.u;
/* There are only 4 base cases when the
* edit distance is 1.
*
* n > m m > n
*
* - |
* \ \ x != u
* \ \
*
* \ \
* \ \ x == u
* - |
*/
if (m > n) {
if (x == u) {
_edit(ctx, DIFF_MATCH, aoff, n);
_edit(ctx, DIFF_INSERT, boff + (m - 1), 1);
} else {
_edit(ctx, DIFF_INSERT, boff, 1);
_edit(ctx, DIFF_MATCH, aoff, n);
}
} else {
if (x == u) {
_edit(ctx, DIFF_MATCH, aoff, m);
_edit(ctx, DIFF_DELETE, aoff + (n - 1), 1);
} else {
_edit(ctx, DIFF_DELETE, aoff, 1);
_edit(ctx, DIFF_MATCH, aoff + 1, m);
}
}
}
}
return d;
}
int
diff(const void *a, int aoff, int n,
const void *b, int boff, int m,
idx_fn idx, cmp_fn cmp, void *context, int dmax,
struct varray *ses, int *sn,
struct varray *buf)
{
struct _ctx ctx;
int d, x, y;
struct diff_edit *e = NULL;
struct varray tmp;
if (!idx != !cmp) { /* ensure both NULL or both non-NULL */
errno = EINVAL;
return -1;
}
ctx.idx = idx;
ctx.cmp = cmp;
ctx.context = context;
if (buf) {
ctx.buf = buf;
} else {
varray_init(&tmp, sizeof(int), NULL);
ctx.buf = &tmp;
}
ctx.ses = ses;
ctx.si = 0;
ctx.dmax = dmax ? dmax : INT_MAX;
if (ses && sn) {
if ((e = varray_get(ses, 0)) == NULL) {
AMSG("");
if (buf == NULL) {
varray_deinit(&tmp);
}
return -1;
}
e->op = 0;
}
/* The _ses function assumes the SES will begin or end with a delete
* or insert. The following will insure this is true by eating any
* beginning matches. This is also a quick to process sequences
* that match entirely.
*/
x = y = 0;
if (cmp) {
while (x < n && y < m && cmp(idx(a, aoff + x, context),
idx(b, boff + y, context), context) == 0) {
x++; y++;
}
} else {
const unsigned char *a0 = (const unsigned char *)a + aoff;
const unsigned char *b0 = (const unsigned char *)b + boff;
while (x < n && y < m && a0[x] == b0[y]) {
x++; y++;
}
}
_edit(&ctx, DIFF_MATCH, aoff, x);
if ((d = _ses(a, aoff + x, n - x, b, boff + y, m - y, &ctx)) == -1) {
AMSG("");
if (buf == NULL) {
varray_deinit(&tmp);
}
return -1;
}
if (ses && sn) {
*sn = e->op ? ctx.si + 1 : 0;
}
if (buf == NULL) {
varray_deinit(&tmp);
}
return d;
}
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