@oazmi/kitchensink/esm/cryptoman.js

a collection of personal utility functions

/** utility functions for cryptography.
 *
 * @module
*/
/** generate a CRC32 hash table for quick lookups. */
import "./_dnt.polyfills.js";
export const createCrc32Table = () => {
    const polynomial = -306674912, crc32_table = new Int32Array(256);
    for (let i = 0; i < 256; i++) {
        // initialize the table with `polynomial` being the starting seed
        let r = i;
        for (let bit = 8; bit > 0; --bit) {
            r = ((r & 1) ? ((r >>> 1) ^ polynomial) : (r >>> 1));
        }
        crc32_table[i] = r;
    }
    return crc32_table;
};
let crc32_table;
/** the CRC32 hash is quick to compute and used frequently in compression functions and their derivatives.
 *
 * you do not have to provide the `bytes` array in its entirety all at once,
 * because you can continue off with the previous partial byte array's crc-hash using the second argument.
 *
 * @param bytes an array of bytes to compute the hash for. can be any kind of array, so long as all byte numbers conform to being unsigned integers that do not exceed the maximum value of `255` (8-bit max value)
 * @param crc provide any previous crc hash that you'd like to continue from, or leave it `undefined` to begin from the standard value of `0xFFFFFFFF` by default
 *
 * @example
 * ```ts
 * import { assertEquals } from "jsr:@std/assert"
 *
 * const
 * 	txtenc = new TextEncoder(),
 * 	crc_a = crc32(txtenc.encode("hello ")),       // == 0xED81F9F6
 * 	crc_b = crc32(txtenc.encode("world"), crc_a), // == 0x0D4A1185
 * 	crc_c = crc32(txtenc.encode("hello world"))   // == 0x0D4A1185
 * assertEquals(crc_b, crc_c)
 * ```
*/
export const crc32 = (bytes, crc) => {
    crc = crc === undefined ? 0xFFFFFFFF : crc ^ -1;
    crc32_table ??= createCrc32Table();
    for (let i = 0; i < bytes.length; ++i) {
        crc = crc32_table[(crc ^ bytes[i]) & 0xFF] ^ (crc >>> 8);
    }
    return (crc ^ -1) >>> 0;
};
// TODO: add your AWS Signature V4 Authorization key generator here in the future