index.js

// FNV_PRIMES and FNV_OFFSETS from
// http://www.isthe.com/chongo/tech/comp/fnv/index.html#FNV-param

const FNV_PRIMES = {
	32: 16_777_619n,
	64: 1_099_511_628_211n,
	128: 309_485_009_821_345_068_724_781_371n,
	256: 374_144_419_156_711_147_060_143_317_175_368_453_031_918_731_002_211n,
	512: 35_835_915_874_844_867_368_919_076_489_095_108_449_946_327_955_754_392_558_399_825_615_420_669_938_882_575_126_094_039_892_345_713_852_759n,
	1024: 5_016_456_510_113_118_655_434_598_811_035_278_955_030_765_345_404_790_744_303_017_523_831_112_055_108_147_451_509_157_692_220_295_382_716_162_651_878_526_895_249_385_292_291_816_524_375_083_746_691_371_804_094_271_873_160_484_737_966_720_260_389_217_684_476_157_468_082_573n,
};

const FNV_OFFSETS = {
	32: 2_166_136_261n,
	64: 14_695_981_039_346_656_037n,
	128: 144_066_263_297_769_815_596_495_629_667_062_367_629n,
	256: 100_029_257_958_052_580_907_070_968_620_625_704_837_092_796_014_241_193_945_225_284_501_741_471_925_557n,
	512: 9_659_303_129_496_669_498_009_435_400_716_310_466_090_418_745_672_637_896_108_374_329_434_462_657_994_582_932_197_716_438_449_813_051_892_206_539_805_784_495_328_239_340_083_876_191_928_701_583_869_517_785n,
	1024: 14_197_795_064_947_621_068_722_070_641_403_218_320_880_622_795_441_933_960_878_474_914_617_582_723_252_296_732_303_717_722_150_864_096_521_202_355_549_365_628_174_669_108_571_814_760_471_015_076_148_029_755_969_804_077_320_157_692_458_563_003_215_304_957_150_157_403_644_460_363_550_505_412_711_285_966_361_610_267_868_082_893_823_963_790_439_336_411_086_884_584_107_735_010_676_915n,
};

const cachedEncoder = new globalThis.TextEncoder();

function fnv1aUint8Array(uint8Array, size) {
	const fnvPrime = FNV_PRIMES[size];
	let hash = FNV_OFFSETS[size];

	// eslint-disable-next-line unicorn/no-for-loop -- This is a performance-sensitive loop
	for (let index = 0; index < uint8Array.length; index++) {
		hash ^= BigInt(uint8Array[index]);
		hash = BigInt.asUintN(size, hash * fnvPrime);
	}

	return hash;
}

function fnv1aEncodeInto(string, size, utf8Buffer) {
	if (utf8Buffer.length === 0) {
		throw new Error('The `utf8Buffer` option must have a length greater than zero');
	}

	const fnvPrime = FNV_PRIMES[size];
	let hash = FNV_OFFSETS[size];
	let remaining = string;

	while (remaining.length > 0) {
		const result = cachedEncoder.encodeInto(remaining, utf8Buffer);
		remaining = remaining.slice(result.read);
		for (let index = 0; index < result.written; index++) {
			hash ^= BigInt(utf8Buffer[index]);
			hash = BigInt.asUintN(size, hash * fnvPrime);
		}
	}

	return hash;
}

export default function fnv1a(value, {size = 32, utf8Buffer} = {}) {
	if (!FNV_PRIMES[size]) {
		throw new Error('The `size` option must be one of 32, 64, 128, 256, 512, or 1024');
	}

	if (typeof value === 'string') {
		if (utf8Buffer) {
			return fnv1aEncodeInto(value, size, utf8Buffer);
		}

		value = cachedEncoder.encode(value);
	}

	return fnv1aUint8Array(value, size);
}