// Simple hash function, from: http://burtleburtle.net/bob/hash/integer.html.
// Chosen because it doesn't use multiply and achieves full avalanche.
export function hashU32(a: number): number {
	a = a | 0;
	a = (a + 2127912214 + (a << 12)) | 0;
	a = a ^ -949894596 ^ (a >>> 19);
	a = (a + 374761393 + (a << 5)) | 0;
	a = (a + -744332180) ^ (a << 9);
	a = (a + -42973499 + (a << 3)) | 0;
	return (a ^ -1252372727 ^ (a >>> 16)) | 0;
}

// Reads a 64-bit little-endian integer from an array.
export function readU64(b: Uint8Array, n: number): number {
	let x = 0;
	x |= b[n++] << 0;
	x |= b[n++] << 8;
	x |= b[n++] << 16;
	x |= b[n++] << 24;
	x |= b[n++] << 32;
	x |= b[n++] << 40;
	x |= b[n++] << 48;
	x |= b[n++] << 56;
	return x;
}

// Reads a 32-bit little-endian integer from an array.
export function readU32(b: Uint8Array, n: number): number {
	let x = 0;
	x |= b[n++] << 0;
	x |= b[n++] << 8;
	x |= b[n++] << 16;
	x |= b[n++] << 24;
	return x;
}

// Writes a 32-bit little-endian integer from an array.
export function writeU32(b: Uint8Array, n: number, x: number): void {
	b[n++] = (x >> 0) & 0xff;
	b[n++] = (x >> 8) & 0xff;
	b[n++] = (x >> 16) & 0xff;
	b[n++] = (x >> 24) & 0xff;
}

// Multiplies two numbers using 32-bit integer multiplication.
// Algorithm from Emscripten.
export function imul(a: number, b: number): number {
	const ah = a >>> 16;
	const al = a & 65535;
	const bh = b >>> 16;
	const bl = b & 65535;

	return (al * bl + ((ah * bl + al * bh) << 16)) | 0;
}