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searchstr.c
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searchstr.c
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#define _GNU_SOURCE
#include <limits.h>
#include <pthread.h>
#include <stdio.h>
#include <stdint.h>
#include <string.h>
#include <signal.h>
#include <sys/types.h>
#include <unistd.h>
/* function: rsearchstr
* Suche Teilstring substr im Gesamtstring data von hinten nach vorn.
* Search substring substr in whole string data in *reverse* order.
* If substr is not found 0 is returned. If substr is contained more than
* once the occurrence with the highest address is reported (reverse order).
*
* Used algorithmus:
* Knuth-Morris-Pratt!
*
* Worst case:
* O(size)
*
* Unchecked Precondition:
* - substrsize >= 1
*
*/
static const uint8_t* rsearchstr(size_t size, const uint8_t data[size], uint8_t substrsize, const uint8_t substr[substrsize])
{
/* For all (0 <= i < substrsize): sidx[i] gives the index into substr
* where you have to continue to compare if comparison failed for index i.
* sidx[substrsize-1] is set to substrsize which marks the end of chain.
*/
uint8_t sidx[substrsize];
sidx[substrsize-1] = substrsize; // 0 length match
for (int i = substrsize-1, i2 = substrsize; i; ) {
while (i2 < substrsize && substr[i] != substr[i2]) {
i2 = sidx[i2];
}
sidx[--i] = (uint8_t) (--i2);
}
size_t dpos = size;
int spos = substrsize;
while (dpos > 0) {
--dpos;
--spos;
if (substr[spos] != data[dpos]) {
spos = sidx[spos];
while (spos < substrsize && substr[spos] != data[dpos]) {
spos = sidx[spos];
}
}
if (! spos) return data + dpos;
}
return 0;
}
/* function: searchstr
* Suche Teilstring substr im Gesamtstring data von vorn nach hinten.
* Search substring substr in whole string data.
* If substr is not found 0 is returned. If substr is contained more than
* once the occurrence with the lowest address is reported.
*
* Used algorithmus:
* Simplified Boyer-Moore without Bad-Character-Heuristic.
* Like KMP but comparing starts from end of substr (substr[substrsize-1]).
*
* Worst case:
* O(size)
*
* Special case (data == 0 || substrsize == 0):
* The value 0 is returned if length of substr or data is 0.
*
*/
const uint8_t* searchstr(size_t size, const uint8_t data[size], uint8_t substrsize, const uint8_t substr[substrsize])
{
// nr of positions substr is to shift right
// array is indexed by nr of matched positions starting from end
uint8_t shift[substrsize];
const uint8_t* pos;
if (substrsize < 2) {
return substrsize ? memchr(data, substr[0], size) : 0;
}
if (substrsize > size) {
return 0;
}
{
pos = memrchr(substr, substr[substrsize-1], substrsize-1);
int lastoff = (pos ? 1 + (int) (pos - substr) : 0);
shift[0] = 1;
shift[1] = (uint8_t) (substrsize - lastoff);
// copied from rsearchstr (KMP index helper array)
uint8_t sidx[substrsize];
sidx[substrsize-1] = substrsize; // 0 length match
for (int i = substrsize-1, i2 = substrsize; i; ) {
while (i2 < substrsize && substr[i] != substr[i2]) {
i2 = sidx[i2];
}
sidx[--i] = (uint8_t) (--i2);
}
for (int nrmatched = 2; nrmatched < substrsize; ++nrmatched) {
if (lastoff >= nrmatched) {
int dpos = lastoff-nrmatched+1;
int spos = substrsize-nrmatched+1;
while (dpos > 0) {
--dpos;
--spos;
if (substr[spos] != substr[dpos]) {
spos = sidx[spos];
while (spos < substrsize && substr[spos] != substr[dpos]) {
spos = sidx[spos];
}
}
if (nrmatched == substrsize-spos) break;
}
lastoff = (spos < substrsize ? dpos+(substrsize-spos) : 0);
}
shift[nrmatched] = (uint8_t) (substrsize - lastoff);
}
}
const int substrsize1 = substrsize-1;
int eoff = 0;
int skip = 0;
const uint8_t* const
endpos = data + size - substrsize1;
pos = data;
do {
int off = substrsize1;
while (substr[off] == pos[off]) {
if (off == eoff) {
if (off <= skip) {
return pos;
}
off -= skip; // make worst case O(size) instead O(size*substrlen)
eoff = 0;
}
--off;
}
int nrmatched = substrsize1 - off;
int pincr = shift[nrmatched];
skip = nrmatched;
pos += pincr;
eoff = substrsize - pincr;
} while (pos < endpos);
return 0;
}
int main()
{
char * s = "ababbbcabaabbbabababbbababbba";
char * p = "ababbba";
printf("rsrch %s\n", rsearchstr(strlen(s), s, strlen(p), p));
printf("rsrch %s\n", rsearchstr(strlen(s)-1, s, strlen(p), p));
const uint8_t* pos1 = searchstr(strlen(s), s, strlen(p), p);
printf("srch %s\n", pos1);
printf("srch %s\n", searchstr(strlen(pos1+1), pos1+1, strlen(p), p));
char data[10000];
memset(data, 'a', sizeof(data));
for (int i = 0; i < 10000; i += 10) {
data[i] = 'b';
}
data[10000-10] = 'a';
data[10000-11] = 'b';
p = "aaaaaaaaaa";
printf("srch %s\n", searchstr(sizeof(data), data, strlen(p), p));
return 0;
}