strverscmp-like in zig

less_than_vers.zig

pub fn less_than_vers(s1: []const u8, s2: []const u8) bool {
    var ii1: usize = 0;
    var ii2: usize = 0;
    const n1 = s1.len;
    const n2 = s2.len;

    while (ii1 < n1 and ii2 < n2) {
        const c1 = s1[ii1];
        const c2 = s2[ii2];

        if (ascii.isDigit(c1) and ascii.isDigit(c2)) {
            const start1 = ii1;
            const start2 = ii2;
            while (ii1 < n1 and s1[ii1] == '0') : (ii1 += 1) {}
            while (ii2 < n2 and s2[ii2] == '0') : (ii2 += 1) {}

            var end1 = ii1;
            var end2 = ii2;
            while (end1 < n1 and ascii.isDigit(s1[end1])) : (end1 += 1) {}
            while (end2 < n2 and ascii.isDigit(s2[end2])) : (end2 += 1) {}

            const len1 = end1 - ii1;
            const len2 = end2 - ii2;
            if (len1 != len2)
                return (len1 < len2);

            while (ii1 < end1 and ii2 < end2) {
                if (s1[ii1] != s2[ii2])
                    return (s1[ii1] < s2[ii2]);

                ii1 += 1;
                ii2 += 1;
            }

            const zlen1 = ii1 - start1;
            const zlen2 = ii2 - start2;
            if (zlen1 != zlen2)
                return (zlen1 < zlen2);
        } else {
            if (c1 != c2)
                return (c1 < c2);

            ii1 += 1;
            ii2 += 1;
        }
    }

    if (ii1 < n1)
        return true;

    return false;
}