Skip to content

Commit

Permalink
Refactor LCG
Browse files Browse the repository at this point in the history
  • Loading branch information
@turiyadev
turiyadev committed Oct 29, 2023
2 parents 782fdd2 + 5bd7bfd commit 06e7488
Show file tree
Hide file tree
Showing 3 changed files with 51 additions and 66 deletions.
2 changes: 1 addition & 1 deletion package.json
View file
Original file line number Diff line number Diff line change
@@ -1,6 +1,6 @@
{
"name": "keymask-base41",
"version": "0.1.0",
"version": "0.1.1",
"description": "Map sequential IDs or serial numbers to and from random-looking Base41-encoded strings",
"type": "module",
"exports": {
Expand Down
106 changes: 50 additions & 56 deletions src/Generator.ts
View file
Original file line number Diff line number Diff line change
Expand Up @@ -17,90 +17,84 @@ const lcgMap: (number[] | bigint[])[] = [
[18446744073709551557n, 811465980874026894n, 18263440312458789471n] // 2^64 - 59
];

function nextNumber(value: number, base: number, map: number[]): number {
value = value * map[1] % map[0] + base;
return value < map[0] ? value : value - map[0] + 1;
}

function nextBigInt(value: bigint, base: bigint, map: bigint[]): bigint {
value = value * map[1] % map[0] + base;
return value < map[0] ? value : value - map[0] + 1n;
}

function previousNumber(value: number, base: number, map: number[]): number {
value -= base;
return (value > 0 ? value : value + map[0] - 1) * map[2] % map[0];
}

function previousBigInt(value: bigint, base: bigint, map: bigint[]): bigint {
value -= base;
return (value > 0 ? value : value + map[0] - 1n) * map[2] % map[0];
}

export class Generator {
private bases: (number | bigint)[];
private offsets: (number | bigint)[];
private bigint: boolean;

constructor(seed?: ArrayBufferLike | ArrayBufferView, bigint: boolean = false) {
if (seed && seed.byteLength < 8) {
throw new RangeError("If a seed is provided it must be at least 8 bytes long.");
}
this.bases = new Array(13) as (number | bigint)[];
if (seed) {
this.offsets = new Array(13) as (number | bigint)[];
if (seed && seed.byteLength > 7) {
if (ArrayBuffer.isView(seed)) {
seed = seed.buffer;
}
seed = seed.slice(0, 8);
const u32 = new Uint32Array(seed);
const u64 = new BigUint64Array(seed);
const n32 = u32[0];
const b64 = u64[0];
this.bases[1] = n32 % 40;
this.bases[2] = n32 % 1020;
this.bases[3] = n32 % 65520;
this.bases[4] = n32 % 2097142;
this.bases[5] = n32 % 67108858;
this.bases[6] = b64 % 4294967290n;
this.bases[7] = b64 % 137438953446n;
this.bases[8] = b64 % 4398046511092n;
this.bases[9] = b64 % 281474976710596n;
this.bases[10] = b64 % 9007199254740880n;
this.bases[11] = b64 % 288230376151711716n;
this.bases[12] = b64 % 18446744073709551556n;
const n32 = new Uint32Array(seed)[0];
const b64 = new BigUint64Array(seed)[0];
this.offsets[1] = n32 % 40;
this.offsets[2] = n32 % 1020;
this.offsets[3] = n32 % 65520;
this.offsets[4] = n32 % 2097142;
this.offsets[5] = n32 % 67108858;
this.offsets[6] = b64 % 4294967290n;
this.offsets[7] = b64 % 137438953446n;
this.offsets[8] = b64 % 4398046511092n;
this.offsets[9] = b64 % 281474976710596n;
this.offsets[10] = b64 % 9007199254740880n;
this.offsets[11] = b64 % 288230376151711716n;
this.offsets[12] = b64 % 18446744073709551556n;
} else {
for (let i = 1; i < 13; i++) {
this.bases[i] = i < 6 ? 0 : 0n;
this.offsets[i] = i < 6 ? 0 : 0n;
}
}
this.bigint = bigint;
}

next(value: number | bigint, mode: number): number | bigint {
if (!value) {
return value;
return mode > 10 || this.bigint ? 0n : 0;
}
const map = lcgMap[mode];
const base = this.bases[mode];
const mod = lcgMap[mode][0];
const mult = lcgMap[mode][1];
const offset = this.offsets[mode];

if (mode > 5) {
const result = nextBigInt(typeof value === "bigint" ? value : BigInt(value), base as bigint, map as bigint[]);
return mode > 10 ? result : Number(result);
if (typeof value === "number") {
value = BigInt(value);
}
value = value * <bigint>mult % <bigint>mod + <bigint>offset;
value = value < <bigint>mod ? value : value - <bigint>mod + 1n;
return mode > 10 || this.bigint ? value : Number(value);
}
if (typeof value === "bigint") {
value = Number(value);
}
return nextNumber(typeof value === "number" ? value : Number(value), base as number, map as number[]);
value = value * <number>mult % <number>mod + <number>offset;
value = value < <number>mod ? value : value - <number>mod + 1;
return this.bigint ? BigInt(value) : value;
}

previous(value: number | bigint, mode: number): number | bigint {
if (!value) {
return value;
return mode > 10 || this.bigint ? 0n : 0;
}
const map = lcgMap[mode];
const base = this.bases[mode];
const mod = lcgMap[mode][0];
const mult = lcgMap[mode][2];
const offset = this.offsets[mode];

if (mode > 5) {
const result = previousBigInt(typeof value === "bigint" ? value : BigInt(value), base as bigint, map as bigint[]);
return mode > 10 || this.bigint ? result : Number(result);
if (typeof value === "number") {
value = BigInt(value);
}
value -= <bigint>offset;
value = (value > 0 ? value : value + <bigint>mod - 1n) * <bigint>mult % <bigint>mod;
return mode > 10 || this.bigint ? value : Number(value);
}
if (typeof value === "bigint") {
value = Number(value);
}
const n = previousNumber(typeof value === "number" ? value : Number(value), base as number, map as number[]);
return this.bigint ? BigInt(n) : n;
value -= <number>offset;
value = (value > 0 ? value : value + <number>mod - 1) * <number>mult % <number>mod;
return this.bigint ? BigInt(value) : value;
}
}
9 changes: 0 additions & 9 deletions test/Generator.test.ts
View file
Original file line number Diff line number Diff line change
Expand Up @@ -10,15 +10,6 @@ describe("Generator", () => {
equal(typeof generator.next, "function");
equal(typeof generator.previous, "function");
});

it("should throw error for invalid seed", () => {
try {
new Generator(new Uint8Array([1, 2, 3]));
} catch (error) {
equal(error instanceof RangeError, true);
equal((error as RangeError).message, "If a seed is provided it must be at least 8 bytes long.");
}
});
});

describe("No offset", () => {
Expand Down

0 comments on commit 06e7488

Please sign in to comment.