@extra-array/bsearch/index.mjs

Binary searches leftmost value in sorted array.

import id from './_id';
import cmp from './_cmp';
/**
 * Binary searches leftmost value in sorted array.
 * @param x an array (sorted)
 * @param v search value
 * @param fc compare function (a, b)
 * @param fm map function (v, i, x)
 * @returns first index of value | ~(index of closest value)
 */
function bsearch(x, v, fc = null, fm = null) {
    var fc = fc || cmp, fm = fm || id;
    var v1 = fm(v, 0, null);
    for (var i = 0, I = x.length; i < I;) {
        var m = i + I >>> 1;
        var u1 = fm(x[m], m, x);
        var c = fc(u1, v1);
        if (c < 0)
            i = m + 1;
        else
            I = m;
    }
    return i >= x.length || fc(fm(x[i], i, x), v1) !== 0 ? ~i : i;
}
export default bsearch;
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