ref: b61ca21ef5e741a68439c84e9f8c79f690215375
dir: diff/diffreg.c
#include <u.h>
#include <libc.h>
#include <bio.h>
#include "diff.h"
/* diff - differential file comparison
*
* Uses an algorithm due to Harold Stone, which finds
* a pair of longest identical subsequences in the two
* files.
*
* The major goal is to generate the match vector J.
* J[i] is the index of the line in file1 corresponding
* to line i file0. J[i] = 0 if there is no
* such line in file1.
*
* Lines are hashed so as to work in core. All potential
* matches are located by sorting the lines of each file
* on the hash (called value). In particular, this
* collects the equivalence classes in file1 together.
* Subroutine equiv replaces the value of each line in
* file0 by the index of the first element of its
* matching equivalence in (the reordered) file1.
* To save space equiv squeezes file1 into a single
* array member in which the equivalence classes
* are simply concatenated, except that their first
* members are flagged by changing sign.
*
* Next the indices that point into member are unsorted into
* array class according to the original order of file0.
*
* The cleverness lies in routine stone. This marches
* through the lines of file0, developing a vector klist
* of "k-candidates". At step i a k-candidate is a matched
* pair of lines x,y (x in file0 y in file1) such that
* there is a common subsequence of lenght k
* between the first i lines of file0 and the first y
* lines of file1, but there is no such subsequence for
* any smaller y. x is the earliest possible mate to y
* that occurs in such a subsequence.
*
* Whenever any of the members of the equivalence class of
* lines in file1 matable to a line in file0 has serial number
* less than the y of some k-candidate, that k-candidate
* with the smallest such y is replaced. The new
* k-candidate is chained (via pred) to the current
* k-1 candidate so that the actual subsequence can
* be recovered. When a member has serial number greater
* that the y of all k-candidates, the klist is extended.
* At the end, the longest subsequence is pulled out
* and placed in the array J by unravel.
*
* With J in hand, the matches there recorded are
* check'ed against reality to assure that no spurious
* matches have crept in due to hashing. If they have,
* they are broken, and "jackpot " is recorded--a harmless
* matter except that a true match for a spuriously
* mated line may now be unnecessarily reported as a change.
*
* Much of the complexity of the program comes simply
* from trying to minimize core utilization and
* maximize the range of doable problems by dynamically
* allocating what is needed and reusing what is not.
* The core requirements for problems larger than somewhat
* are (in words) 2*length(file0) + length(file1) +
* 3*(number of k-candidates installed), typically about
* 6n words for files of length n.
*/
static void
sort(Line *a, int n) /*shellsort CACM #201*/
{
int m;
Line *ai, *aim, *j, *k;
Line w;
int i;
m = 0;
for (i = 1; i <= n; i *= 2)
m = 2*i - 1;
for (m /= 2; m != 0; m /= 2) {
k = a+(n-m);
for (j = a+1; j <= k; j++) {
ai = j;
aim = ai+m;
do {
if (aim->value > ai->value ||
aim->value == ai->value &&
aim->serial > ai->serial)
break;
w = *ai;
*ai = *aim;
*aim = w;
aim = ai;
ai -= m;
} while (ai > a && aim >= ai);
}
}
}
static void
unsort(Line *f, int l, int *b)
{
int *a;
int i;
a = malloc((l+1)*sizeof(int));
for(i=1;i<=l;i++)
a[f[i].serial] = f[i].value;
for(i=1;i<=l;i++)
b[i] = a[i];
free(a);
}
static void
prune(Diff *d)
{
int i,j;
for(d->pref = 0; d->pref < d->len[0] && d->pref < d->len[1] &&
d->file[0][d->pref+1].value == d->file[1][d->pref+1].value;
d->pref++) ;
for(d->suff=0; d->suff < d->len[0] - d->pref && d->suff < d->len[1] - d->pref &&
d->file[0][d->len[0] - d->suff].value == d->file[1][d->len[1] - d->suff].value;
d->suff++) ;
for(j=0;j<2;j++) {
d->sfile[j] = d->file[j]+d->pref;
d->slen[j] = d->len[j]-d->pref-d->suff;
for(i=0;i<=d->slen[j];i++)
d->sfile[j][i].serial = i;
}
}
static void
equiv(Line *a, int n, Line *b, int m, int *c)
{
int i, j;
i = j = 1;
while(i<=n && j<=m) {
if(a[i].value < b[j].value)
a[i++].value = 0;
else if(a[i].value == b[j].value)
a[i++].value = j;
else
j++;
}
while(i <= n)
a[i++].value = 0;
b[m+1].value = 0;
j = 0;
while(++j <= m) {
c[j] = -b[j].serial;
while(b[j+1].value == b[j].value) {
j++;
c[j] = b[j].serial;
}
}
c[j] = -1;
}
static int
newcand(Diff *d, int x, int y, int pred)
{
Cand *q;
d->clist = erealloc(d->clist, (d->clen+1)*sizeof(Cand));
q = d->clist + d->clen;
q->x = x;
q->y = y;
q->pred = pred;
return d->clen++;
}
static int
search(Diff *d, int *c, int k, int y)
{
int i, j, l;
int t;
if(d->clist[c[k]].y < y) /*quick look for typical case*/
return k+1;
i = 0;
j = k+1;
while((l=(i+j)/2) > i) {
t = d->clist[c[l]].y;
if(t > y)
j = l;
else if(t < y)
i = l;
else
return l;
}
return l+1;
}
static int
stone(Diff *d, int *a, int n, int *b, int *c)
{
int i, k,y;
int j, l;
int oldc, tc;
int oldl;
k = 0;
c[0] = newcand(d, 0, 0, 0);
for(i=1; i<=n; i++) {
j = a[i];
if(j==0)
continue;
y = -b[j];
oldl = 0;
oldc = c[0];
do {
if(y <= d->clist[oldc].y)
continue;
l = search(d, c, k, y);
if(l!=oldl+1)
oldc = c[l-1];
if(l<=k) {
if(d->clist[c[l]].y <= y)
continue;
tc = c[l];
c[l] = newcand(d, i, y, oldc);
oldc = tc;
oldl = l;
} else {
c[l] = newcand(d, i,y,oldc);
k++;
break;
}
} while((y=b[++j]) > 0);
}
return k;
}
static void
unravel(Diff *d, int p)
{
int i;
Cand *q;
for(i=0; i<=d->len[0]; i++) {
if (i <= d->pref)
d->J[i] = i;
else if (i > d->len[0]-d->suff)
d->J[i] = i+d->len[1] - d->len[0];
else
d->J[i] = 0;
}
for(q=d->clist+p; q->y != 0; q= d->clist + q->pred)
d->J[q->x+d->pref] = q->y+d->pref;
}
#define BUF 4096
static int
cmp(Biobuf* b1, Biobuf* b2)
{
int n;
uchar buf1[BUF], buf2[BUF];
int f1, f2;
vlong nc = 1;
uchar *b1s, *b1e, *b2s, *b2e;
f1 = Bfildes(b1);
f2 = Bfildes(b2);
seek(f1, 0, 0);
seek(f2, 0, 0);
b1s = b1e = buf1;
b2s = b2e = buf2;
for(;;){
if(b1s >= b1e){
if(b1s >= &buf1[BUF])
b1s = buf1;
n = read(f1, b1s, &buf1[BUF] - b1s);
b1e = b1s + n;
}
if(b2s >= b2e){
if(b2s >= &buf2[BUF])
b2s = buf2;
n = read(f2, b2s, &buf2[BUF] - b2s);
b2e = b2s + n;
}
n = b2e - b2s;
if(n > b1e - b1s)
n = b1e - b1s;
if(n <= 0)
break;
if(memcmp((void *)b1s, (void *)b2s, n) != 0){
return 1;
}
nc += n;
b1s += n;
b2s += n;
}
if(b1e - b1s == b2e - b2s)
return 0;
return 1;
}
void
calcdiff(Diff *d, char *f, char *fo, char *t, char *to)
{
Biobuf *b0, *b1;
int k;
b0 = prepare(d, 0, f, fo);
if (!b0)
return;
b1 = prepare(d, 1, t, to);
if (!b1) {
Bterm(b0);
return;
}
if (d->binary){
// could use b0 and b1 but this is simpler.
if (cmp(b0, b1))
print("binary files %s %s differ\n", f, t);
Bterm(b0);
Bterm(b1);
return;
}
d->clen = 0;
prune(d);
sort(d->sfile[0], d->slen[0]);
sort(d->sfile[1], d->slen[1]);
d->member = (int *)d->file[1];
equiv(d->sfile[0], d->slen[0], d->sfile[1], d->slen[1], d->member);
d->member = erealloc(d->member, (d->slen[1]+2)*sizeof(int));
d->class = (int *)d->file[0];
unsort(d->sfile[0], d->slen[0], d->class);
d->class = erealloc(d->class, (d->slen[0]+2)*sizeof(int));
d->klist = emalloc((d->slen[0]+2)*sizeof(int));
d->clist = emalloc(sizeof(Cand));
k = stone(d, d->class, d->slen[0], d->member, d->klist);
free(d->member);
free(d->class);
d->J = emalloc((d->len[0]+2)*sizeof(int));
unravel(d, d->klist[k]);
free(d->clist);
free(d->klist);
d->ixold = emalloc((d->len[0]+2)*sizeof(long));
d->ixnew = emalloc((d->len[1]+2)*sizeof(long));
Bseek(b0, 0, 0); Bseek(b1, 0, 0);
check(d, b0, b1);
}
static void
output(Diff *d)
{
int m, i0, i1, j0, j1;
m = d->len[0];
d->J[0] = 0;
d->J[m+1] = d->len[1]+1;
if (mode != 'e') {
for (i0 = 1; i0 <= m; i0 = i1+1) {
while (i0 <= m && d->J[i0] == d->J[i0-1]+1)
i0++;
j0 = d->J[i0-1]+1;
i1 = i0-1;
while (i1 < m && d->J[i1+1] == 0)
i1++;
j1 = d->J[i1+1]-1;
d->J[i1] = j1;
change(d, i0, i1, j0, j1);
}
} else {
for (i0 = m; i0 >= 1; i0 = i1-1) {
while (i0 >= 1 && d->J[i0] == d->J[i0+1]-1 && d->J[i0])
i0--;
j0 = d->J[i0+1]-1;
i1 = i0+1;
while (i1 > 1 && d->J[i1-1] == 0)
i1--;
j1 = d->J[i1-1]+1;
d->J[i1] = j1;
change(d, i1 , i0, j1, j0);
}
}
if (m == 0)
change(d, 1, 0, 1, d->len[1]);
flushchanges(d);
}
void
diffreg(char *f, char *fo, char *t, char *to)
{
Diff d;
memset(&d, 0, sizeof(d));
calcdiff(&d, f, fo, t, to);
output(&d);
freediff(&d);
}
void
freediff(Diff *d)
{
Bterm(d->input[0]);
Bterm(d->input[1]);
free(d->J);
free(d->ixold);
free(d->ixnew);
}