diff options
Diffstat (limited to 'src/string/wcsstr.c')
-rw-r--r-- | src/string/wcsstr.c | 117 |
1 files changed, 117 insertions, 0 deletions
diff --git a/src/string/wcsstr.c b/src/string/wcsstr.c new file mode 100644 index 0000000..966174f --- /dev/null +++ b/src/string/wcsstr.c @@ -0,0 +1,117 @@ +#include <wchar.h> +#include <string.h> +#include <stdlib.h> +#include <stdint.h> + +static wchar_t *naive_wcsstr(const wchar_t *h, const wchar_t *n) +{ + size_t i; + for (i=0; n[i] && h[i]; i++) + for ( ; n[i] != h[i]; h++, i=0); + return n[i] ? 0 : (wchar_t *)h; +} + +#define MAX(a,b) ((a)>(b)?(a):(b)) +#define MIN(a,b) ((a)<(b)?(a):(b)) + +static wchar_t *twoway_wcsstr(const wchar_t *h, const wchar_t *n) +{ + const wchar_t *z; + size_t l, ip, jp, k, p, ms, p0, mem, mem0; + + /* Computing length of needle */ + for (l=0; n[l] && h[l]; l++); + if (n[l]) return 0; /* hit the end of h */ + + /* 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 (wmemcmp(n, n+p, ms+1)) { + mem0 = 0; + p = MAX(ms, l-ms-1) + 1; + } else mem0 = l-p; + mem = 0; + + /* Initialize incremental end-of-haystack pointer */ + z = h; + + /* Search loop */ + for (;;) { + /* Update incremental end-of-haystack pointer */ + if (z-h < l) { + /* Fast estimate for MIN(l,63) */ + size_t grow = l | 63; + const wchar_t *z2 = wmemchr(z, 0, grow); + if (z2) { + z = z2; + if (z-h < l) return 0; + } else z += grow; + } + + /* 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 (wchar_t *)h; + h += p; + mem = mem0; + } +} + +wchar_t *wcsstr(const wchar_t *h, const wchar_t *n) +{ + /* Return immediately on empty needle or haystack */ + if (!n[0]) return (wchar_t *)h; + if (!h[0]) return 0; + + /* Use faster algorithms for short needles */ + h = wcschr(h, *n); + if (!h || !n[1]) return (wchar_t *)h; + if (!h[1]) return 0; + if (!n[2] || !n[3] || !n[4]) return naive_wcsstr(h, n); + + return twoway_wcsstr(h, n); +} |