Iterative Segment Tree Range Sum in JavaScript

"use strict";
// Iterative Segment Tree Range Sum in JavaScript
//
// PURPOSE
// A segment tree range query combines the small number of disjoint nodes covering a half-
// open interval.
//
// METHOD
// Move both endpoints to leaves. Include a left endpoint when it is a right child and a
// right endpoint when it is about to cross a left child, then move both up.
//
// COMPLEXITY
// O(log n) time, O(1) auxiliary space.
//
// CONTRACT
// tree has 2*n entries; n>=1, 0<=left<=right<=n. Returns sum in [left,right). Empty range
// returns zero.
// 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: 5.
// 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 segment_sum(tree, left, right) {
    alg_require(tree instanceof Int32Array);
    alg_require(Number.isInteger(left) && left >= -2147483648 && left <= 2147483647);
    alg_require(Number.isInteger(right) && right >= -2147483648 && right <= 2147483647);
    let n = Math.floor(tree.length / 2);
    alg_require(((n >= 0) && (n <= 1000000)));
    alg_require((tree.length == alg_mul(2, n)));
    alg_require(((n >= 1) && (left >= 0) && (left <= right) && (right <= n)));
    left = alg_add(left, n);
    right = alg_add(right, n);
    let total = 0;
    while ((left < right)) {
        if (((left % 2) == 1)) {
            total = alg_add(total, tree[left]);
            left = alg_add(left, 1);
        }
        if (((right % 2) == 1)) {
            right = alg_sub(right, 1);
            total = alg_add(total, tree[right]);
        }
        left = Math.floor(left / 2);
        right = Math.floor(right / 2);
    }
    return total;
}

let tree = new Int32Array([0, 10, 3, 7, 1, 2, 3, 4]);
let left = 1;
let right = 3;
let result = segment_sum(tree, left, right);
console.log(result);