diff options
| -rw-r--r-- | include/string.h | 1 | ||||
| -rw-r--r-- | src/string/memmem.c | 148 |
2 files changed, 149 insertions, 0 deletions
diff --git a/include/string.h b/include/string.h index 3a0868b7..33f01378 100644 --- a/include/string.h +++ b/include/string.h @@ -95,6 +95,7 @@ int strcasecmp_l (const char *, const char *, locale_t); int strncasecmp_l (const char *, const char *, size_t, locale_t); char *strchrnul(const char *, int); char *strcasestr(const char *, const char *); +void *memmem(const void *, size_t, const void *, size_t); void *memrchr(const void *, int, size_t); void *mempcpy(void *, const void *, size_t); #ifndef __cplusplus diff --git a/src/string/memmem.c b/src/string/memmem.c new file mode 100644 index 00000000..861fef2f --- /dev/null +++ b/src/string/memmem.c @@ -0,0 +1,148 @@ +#define _GNU_SOURCE +#include <string.h> +#include <stdlib.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 (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); n[k] && n[k] == h[k]; k++); + if (n[k]) { + 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 *memmem(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; + 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); +} |