Binary GCD in JavaScript

"use strict";
// Binary GCD in JavaScript
//
// PURPOSE
// Binary GCD replaces general remainders with parity tests, division by two, and
// subtraction.
//
// METHOD
// Remove common factors of two, make the first operand odd, repeatedly make the second odd
// and subtract the smaller odd operand, then restore the common power of two.
//
// COMPLEXITY
// O(log(max(a,b))) iterations under fixed-width arithmetic, O(1) space.
//
// CONTRACT
// Nonnegative integers. gcd(0,0)=0.
// Public APIs infer array lengths except in C, which accepts pointer/length pairs. Vertex
// counts and matrix dimensions remain explicit. Arrays must contain signed 32-bit integers.
// Sorted order, correct tree topology, and caller-owned data-structure invariants are
// preconditions; checking them on every query would change query complexity.
// Scalar and shape checks are included. Value-range checks are included where needed to
// prevent invalid indexing or nontermination. Allocation sizes are capped at 4,000,000
// workspace entries. Arithmetic outside Python raises an error on 32-bit overflow; Python
// uses arbitrary precision. Native allocation failures propagate. In-place outputs may be
// partly updated after arithmetic failure. These are single-threaded, in-memory
// implementations.
//
// LANGUAGE DETAILS
// Node.js 18+: Int32Array inputs and workspaces provide compact integer storage. Automatic
// lengths and checked arithmetic reject values outside signed 32-bit. Invalid inputs or
// overflow throw RangeError.
//
// EXAMPLE
// Expected return: 6.
// Run: node example.js
// Tests for this exact source artifact run before publication. The accompanying source
// archive includes unit cases, runtime results, and source hashes.

function alg_require(valid) { if (!valid) throw new RangeError("invalid algorithm input"); }
function alg_checked(v) { if (!Number.isInteger(v) || v < -2147483648 || v > 2147483647) throw new RangeError("32-bit result overflow"); return v; }
function alg_add(a,b) { return alg_checked(a+b); }
function alg_sub(a,b) { return alg_checked(a-b); }
function alg_mul(a,b) { return alg_checked(a*b); }
function alg_size(n) { alg_require(Number.isInteger(n) && n>=0 && n<=4000000); return n; }

function binary_gcd(a, b) {
    alg_require(Number.isInteger(a) && a >= -2147483648 && a <= 2147483647);
    alg_require(Number.isInteger(b) && b >= -2147483648 && b <= 2147483647);
    alg_require(((a >= 0) && (b >= 0)));
    if ((a == 0)) {
        return b;
    }
    if ((b == 0)) {
        return a;
    }
    let factor = 1;
    let temp = 0;
    while ((((a % 2) == 0) && ((b % 2) == 0))) {
        a = Math.floor(a / 2);
        b = Math.floor(b / 2);
        factor = alg_mul(factor, 2);
    }
    while (((a % 2) == 0)) {
        a = Math.floor(a / 2);
    }
    while ((b != 0)) {
        while (((b % 2) == 0)) {
            b = Math.floor(b / 2);
        }
        if ((a > b)) {
            temp = a;
            a = b;
            b = temp;
        }
        b = alg_sub(b, a);
    }
    return alg_mul(a, factor);
}

let a = 48;
let b = 18;
let result = binary_gcd(a, b);
console.log(result);