third_party/ulib/musl/src/string/wcsstr.c

#include <wchar.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* restrict h, const wchar_t* restrict 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;

    return twoway_wcsstr(h, n);
}