/**
* \brief Get a block of data if possible, and see if it matches.
*
* On each call, we try to process all of the input data available on the
* scoop and input buffer. */
static rs_result rs_delta_s_scan(rs_job_t *job)
{
rs_long_t match_pos;
size_t match_len;
rs_result result;
Rollsum test;
rs_job_check(job);
/* read the input into the scoop */
rs_getinput(job);
/* output any pending output from the tube */
result=rs_tube_catchup(job);
/* while output is not blocked and there is a block of data */
while ((result==RS_DONE) &&
((job->scoop_pos + job->block_len) < job->scoop_avail)) {
/* check if this block matches */
if (rs_findmatch(job,&match_pos,&match_len)) {
/* append the match and reset the weak_sum */
result=rs_appendmatch(job,match_pos,match_len);
RollsumInit(&job->weak_sum);
} else {
/* rotate the weak_sum and append the miss byte */
RollsumRotate(&job->weak_sum,job->scoop_next[job->scoop_pos],
job->scoop_next[job->scoop_pos+job->block_len]);
result=rs_appendmiss(job,1);
if (rs_roll_paranoia) {
RollsumInit(&test);
RollsumUpdate(&test,job->scoop_next+job->scoop_pos,
job->block_len);
if (RollsumDigest(&test) != RollsumDigest(&job->weak_sum)) {
rs_fatal("mismatch between rolled sum %#x and check %#x",
(int)RollsumDigest(&job->weak_sum),
(int)RollsumDigest(&test));
}
}
}
}
/* if we completed OK */
if (result==RS_DONE) {
/* if we reached eof, we can flush the last fragment */
if (job->stream->eof_in) {
job->statefn=rs_delta_s_flush;
return RS_RUNNING;
} else {
/* we are blocked waiting for more data */
return RS_BLOCKED;
}
}
return result;
}
/**
* find a match at scoop_pos, returning the match_pos and match_len.
* Note that this will calculate weak_sum if required. It will also
* determine the match_len.
*
* Note that this routine could be modified to do xdelta style matches that
* would extend matches past block boundaries by matching backwards and
* forwards beyond the block boundaries. Extending backwards would require
* decrementing scoop_pos as appropriate.
*/
INLINE int rs_findmatch(rs_job_t *job, rs_long_t *match_pos, size_t *match_len) {
/* calculate the weak_sum if we don't have one */
if (job->weak_sum.count == 0) {
/* set match_len to min(block_len, scan_avail) */
*match_len=job->scoop_avail - job->scoop_pos;
if (*match_len > job->block_len) {
*match_len = job->block_len;
}
/* Update the weak_sum */
RollsumUpdate(&job->weak_sum,job->scoop_next+job->scoop_pos,*match_len);
rs_trace("calculate weak sum from scratch length %d",(int)job->weak_sum.count);
} else {
/* set the match_len to the weak_sum count */
*match_len=job->weak_sum.count;
}
return rs_search_for_block(RollsumDigest(&job->weak_sum),
job->scoop_next+job->scoop_pos,
*match_len,
job->signature,
&job->stats,
match_pos);
}
int main(int argc, char *argv[])
{
int i;
Rollsum sum;
char c,data[BLOCKSIZE];
unsigned long digest;
if (argc != 1) {
usage();
}
for (i=0;i<BLOCKSIZE;i++) {
data[i]=(char)(i & 0xff);
}
RollsumInit(&sum);
RollsumUpdate(&sum,data,BLOCKSIZE);
for (i=0;i<(COUNT*BLOCKSIZE);i++) {
c=data[i % BLOCKSIZE];
RollsumRotate(&sum,c,c);
digest=RollsumDigest(&sum);
}
printf("rollsum: %i x %i rotate gives %X\n",COUNT,BLOCKSIZE,digest);
}