Prefix Sum Range Query in JavaScript

"use strict";
// Prefix Sum Range Query in JavaScript
//
// PURPOSE
// Prefix sums turn a range sum into a subtraction. The preprocessed prefix at index i stores
// the sum of all elements before i.
//
// METHOD
// Build prefix[i+1] = prefix[i] + a[i]. For inclusive bounds left and right, subtract
// prefix[left] from prefix[right+1]. Build once and reuse the prefix for many queries in a
// real application.
//
// COMPLEXITY
// O(n) preprocessing and O(n) space; each query after preprocessing is O(1). This self-
// contained function includes preprocessing on every call.
//
// CONTRACT
// 0 <= left <= right < n. Returns the inclusive range sum. All prefix totals must fit.
// 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 range_sum(a, left, right) {
    alg_require(a instanceof Int32Array);
    alg_require(Number.isInteger(left) && left >= -2147483648 && left <= 2147483647);
    alg_require(Number.isInteger(right) && right >= -2147483648 && right <= 2147483647);
    let n = a.length;
    alg_require(((n >= 0) && (n <= 1000000)));
    alg_require((a.length == n));
    alg_require(((left >= 0) && (left <= right) && (right < n)));
    let prefix = new Int32Array(alg_size(alg_add(n, 1)));
    let i = 0;
    while ((i < n)) {
        prefix[alg_add(i, 1)] = alg_add(prefix[i], a[i]);
        i = alg_add(i, 1);
    }
    return alg_sub(prefix[alg_add(right, 1)], prefix[left]);
}

let a = new Int32Array([2, 4, -1, 3]);
let left = 1;
let right = 3;
let result = range_sum(a, left, right);
console.log(result);