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-rw-r--r--mymemmem.c173
1 files changed, 173 insertions, 0 deletions
diff --git a/mymemmem.c b/mymemmem.c
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+++ b/mymemmem.c
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+// taken straight from musl@c718f9fc
+
+/*
+Copyright © 2005-2014 Rich Felker, et al.
+
+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.
+*/
+
+#include <string.h>
+#include <stdint.h>
+
+static char *twobyte_memmem(const unsigned char *h, size_t k, const unsigned char *n)
+{
+ uint16_t nw = n[0]<<8 | n[1], hw = h[0]<<8 | h[1];
+ for (h++, k--; k; k--, hw = hw<<8 | *++h)
+ if (hw == nw) return (char *)h-1;
+ return 0;
+}
+
+static char *threebyte_memmem(const unsigned char *h, size_t k, const unsigned char *n)
+{
+ uint32_t nw = n[0]<<24 | n[1]<<16 | n[2]<<8;
+ uint32_t hw = h[0]<<24 | h[1]<<16 | h[2]<<8;
+ for (h+=2, k-=2; k; k--, hw = (hw|*++h)<<8)
+ if (hw == nw) return (char *)h-2;
+ return 0;
+}
+
+static char *fourbyte_memmem(const unsigned char *h, size_t k, const unsigned char *n)
+{
+ uint32_t nw = n[0]<<24 | n[1]<<16 | n[2]<<8 | n[3];
+ uint32_t hw = h[0]<<24 | h[1]<<16 | h[2]<<8 | h[3];
+ for (h+=3, k-=3; k; k--, hw = hw<<8 | *++h)
+ if (hw == nw) return (char *)h-3;
+ return 0;
+}
+
+#define MAX(a,b) ((a)>(b)?(a):(b))
+#define MIN(a,b) ((a)<(b)?(a):(b))
+
+#define BITOP(a,b,op) \
+ ((a)[(size_t)(b)/(8*sizeof *(a))] op (size_t)1<<((size_t)(b)%(8*sizeof *(a))))
+
+static char *twoway_memmem(const unsigned char *h, const unsigned char *z, const unsigned char *n, size_t l)
+{
+ size_t i, ip, jp, k, p, ms, p0, mem, mem0;
+ size_t byteset[32 / sizeof(size_t)] = { 0 };
+ size_t shift[256];
+
+ /* Computing length of needle and fill shift table */
+ for (i=0; i<l; i++)
+ BITOP(byteset, n[i], |=), shift[n[i]] = i+1;
+
+ /* Compute maximal suffix */
+ ip = -1; jp = 0; k = p = 1;
+ while (jp+k<l) {
+ if (n[ip+k] == n[jp+k]) {
+ if (k == p) {
+ jp += p;
+ k = 1;
+ } else k++;
+ } else if (n[ip+k] > n[jp+k]) {
+ jp += k;
+ k = 1;
+ p = jp - ip;
+ } else {
+ ip = jp++;
+ k = p = 1;
+ }
+ }
+ ms = ip;
+ p0 = p;
+
+ /* And with the opposite comparison */
+ ip = -1; jp = 0; k = p = 1;
+ while (jp+k<l) {
+ if (n[ip+k] == n[jp+k]) {
+ if (k == p) {
+ jp += p;
+ k = 1;
+ } else k++;
+ } else if (n[ip+k] < n[jp+k]) {
+ jp += k;
+ k = 1;
+ p = jp - ip;
+ } else {
+ ip = jp++;
+ k = p = 1;
+ }
+ }
+ if (ip+1 > ms+1) ms = ip;
+ else p = p0;
+
+ /* Periodic needle? */
+ if (memcmp(n, n+p, ms+1)) {
+ mem0 = 0;
+ p = MAX(ms, l-ms-1) + 1;
+ } else mem0 = l-p;
+ mem = 0;
+
+ /* Search loop */
+ for (;;) {
+ /* If remainder of haystack is shorter than needle, done */
+ if ((size_t)(z-h) < l) return 0;
+
+ /* Check last byte first; advance by shift on mismatch */
+ if (BITOP(byteset, h[l-1], &)) {
+ k = l-shift[h[l-1]];
+ if (k) {
+ if (mem0 && mem && k < p) k = l-p;
+ h += k;
+ mem = 0;
+ continue;
+ }
+ } else {
+ h += l;
+ mem = 0;
+ continue;
+ }
+
+ /* Compare right half */
+ for (k=MAX(ms+1,mem); k<l && n[k] == h[k]; k++);
+ if (k < l) {
+ h += k-ms;
+ mem = 0;
+ continue;
+ }
+ /* Compare left half */
+ for (k=ms+1; k>mem && n[k-1] == h[k-1]; k--);
+ if (k <= mem) return (char *)h;
+ h += p;
+ mem = mem0;
+ }
+}
+
+void *mymemmem(const void *h0, size_t k, const void *n0, size_t l)
+{
+ const unsigned char *h = h0, *n = n0;
+
+ /* Return immediately on empty needle */
+ if (!l) return (void *)h;
+
+ /* Return immediately when needle is longer than haystack */
+ if (k<l) return 0;
+
+ /* Use faster algorithms for short needles */
+ h = memchr(h0, *n, k);
+ if (!h || l==1) return (void *)h;
+ k -= h - (const unsigned char *)h0;
+ if (k<l) return 0;
+ if (l==2) return twobyte_memmem(h, k, n);
+ if (l==3) return threebyte_memmem(h, k, n);
+ if (l==4) return fourbyte_memmem(h, k, n);
+
+ return twoway_memmem(h, h+k, n, l);
+}