Find the index of the closest or exact match in an ordered list.

FindClosest.js

function findClosest(haystack, needle, comp, lo, hi) {

    var mid, cmp;
    lo = lo || 0;
    hi = hi || haystack.length - 1;

    while(lo <= hi) {
        mid = lo + (hi - lo>>1);
        cmp = comp(haystack[mid], needle);

        if(cmp < 0)
            lo = mid + 1;

        else if(cmp > 0)
            hi = mid - 1;

        else
            return mid;
    }

    return lo;
}