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David Brockman Smoliansky
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MIT License | ||
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Copyright (c) 2019 David Brockman Smoliansky | ||
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Permission is hereby granted, free of charge, to any person obtaining a copy | ||
of this software and associated documentation files (the "Software"), to deal | ||
in the Software without restriction, including without limitation the rights | ||
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell | ||
copies of the Software, and to permit persons to whom the Software is | ||
furnished to do so, subject to the following conditions: | ||
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The above copyright notice and this permission notice shall be included in all | ||
copies or substantial portions of the Software. | ||
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THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR | ||
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, | ||
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE | ||
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER | ||
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, | ||
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE | ||
SOFTWARE. |
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# `@dbrockman/varint` | ||
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Encode integers of varying sizes. | ||
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This is copied from [varint](https://github.com/chrisdickinson/varint) and [signed-varint](https://github.com/dominictarr/signed-varint) with minor tweaks to the interface. | ||
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```sh | ||
yarn add @dbrockman/varint | ||
``` |
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{ | ||
"name": "@dbrockman/varint", | ||
"version": "1.0.1", | ||
"description": "Encode integers of varying sizes.", | ||
"private": true, | ||
"main": "build/main.js", | ||
"types": "build/main.d.ts", | ||
"files": ["build"], | ||
"scripts": { | ||
"clean": "del 'build'", | ||
"build": "tsc -p tsconfig.build.json", | ||
"prebuild": "yarn run clean", | ||
"postbuild": "del 'build/**/__*__/'" | ||
}, | ||
"dependencies": {}, | ||
"devDependencies": {}, | ||
"publishConfig": { | ||
"access": "public" | ||
}, | ||
"license": "MIT", | ||
"repository": "git@github.com:dbrockman/monode.git", | ||
"homepage": "https://github.com/dbrockman/monode/tree/master/code/varint#readme" | ||
} |
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import { readSignedVarint, signedVarintByteLength, writeSignedVarint } from "../main"; | ||
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function encodeDecode(v: number, bytes: number) { | ||
const a = []; | ||
const c = writeSignedVarint(v, a, 0); | ||
expect(a.length).toBe(bytes); | ||
expect(readSignedVarint(a, 0)).toEqual({ length: bytes, value: v }); | ||
expect(c).toBe(bytes); | ||
expect(signedVarintByteLength(v)).toBe(bytes); | ||
} | ||
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test("single byte", () => { | ||
encodeDecode(1, 1); | ||
encodeDecode(-1, 1); | ||
encodeDecode(63, 1); | ||
encodeDecode(-64, 1); | ||
}); | ||
test("double byte", () => { | ||
encodeDecode(64, 2); | ||
encodeDecode(-65, 2); | ||
encodeDecode(127, 2); | ||
encodeDecode(-128, 2); | ||
encodeDecode(128, 2); | ||
encodeDecode(-129, 2); | ||
encodeDecode(255, 2); | ||
encodeDecode(-256, 2); | ||
}); | ||
test("tripple", () => { | ||
encodeDecode(0x4000, 3); | ||
encodeDecode(-0x4001, 3); | ||
encodeDecode(1048574, 3); | ||
encodeDecode(-1048575, 3); | ||
}); | ||
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test("quad", () => { | ||
encodeDecode(134217726, 4); | ||
encodeDecode(-134217727, 4); | ||
}); | ||
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test("large int", () => { | ||
encodeDecode(0x80000000000, 7); | ||
encodeDecode(-0x80000000000, 7); | ||
}); |
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import { readUnsignedVarint, unsignedVarintByteLength, writeUnsignedVarint } from "../main"; | ||
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test("fuzz test", () => { | ||
for (var i = 0, len = 100; i < len; ++i) { | ||
const num = randint(0x7fffffff); | ||
const encoded = []; | ||
const bytes_written = writeUnsignedVarint(num, encoded, 0); | ||
expect(encoded.length).toBe(bytes_written); | ||
expect(bytes_written).toBe(unsignedVarintByteLength(num)); | ||
expect(readUnsignedVarint(encoded, 0)).toEqual({ length: bytes_written, value: num }); | ||
} | ||
}); | ||
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test("test single byte works as expected", () => { | ||
const buf = new Uint8Array(2); | ||
buf[0] = 172; | ||
buf[1] = 2; | ||
expect(readUnsignedVarint(buf, 0)).toEqual({ length: 2, value: 300 }); | ||
}); | ||
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test("test encode works as expected", () => { | ||
const out = []; | ||
const n_bytes = writeUnsignedVarint(300, out, 0); | ||
expect(n_bytes).toBe(2); | ||
expect(out).toEqual([0xac, 0x02]); | ||
}); | ||
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test("test decode single bytes", () => { | ||
const num = randint(127); | ||
const buf = new Uint8Array(1); | ||
buf[0] = num; | ||
expect(readUnsignedVarint(buf, 0)).toEqual({ length: 1, value: num }); | ||
}); | ||
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test("test decode multiple bytes with zero", () => { | ||
const num = randint(127); | ||
const buf = new Uint8Array(2); | ||
buf[0] = 128; | ||
buf[1] = num; | ||
expect(readUnsignedVarint(buf, 0)).toEqual({ length: 2, value: num << 7 }); | ||
}); | ||
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test("encode single byte", () => { | ||
const expected = randint(127); | ||
const arr = []; | ||
expect(writeUnsignedVarint(expected, arr, 0)).toBe(1); | ||
expect(arr).toEqual([expected]); | ||
}); | ||
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test("encode multiple byte with zero first byte", () => { | ||
const expected = 0x0f00; | ||
const arr = []; | ||
expect(writeUnsignedVarint(expected, arr, 0)).toBe(2); | ||
expect(arr).toEqual([0x80, 0x1e]); | ||
}); | ||
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test("big integers", () => { | ||
const bigs: number[] = []; | ||
for (var i = 32; i <= 53; i++) { | ||
const n = 2 ** i; | ||
bigs.push(n - 1, n); | ||
} | ||
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bigs.forEach((n) => { | ||
const arr = []; | ||
writeUnsignedVarint(n, arr, 0); | ||
const { length, value } = readUnsignedVarint(arr, 0); | ||
expect(length).toBe(arr.length); | ||
expect(value).toBe(n); | ||
expect(value).not.toBe(n - 1); | ||
}); | ||
}); | ||
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test("fuzz test - big", () => { | ||
const MAX_INTD = 2 ** 55; | ||
const MAX_INT = 2 ** 31; | ||
for (var i = 0, len = 100; i < len; ++i) { | ||
const expected = randint(MAX_INTD - MAX_INT) + MAX_INT; | ||
const arr = []; | ||
writeUnsignedVarint(expected, arr, 0); | ||
expect(readUnsignedVarint(arr, 0)).toEqual({ length: arr.length, value: expected }); | ||
} | ||
}); | ||
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test("unsignedVarintByteLength", () => { | ||
for (var i = 0; i <= 53; i++) { | ||
const n = 2 ** i; | ||
const arr = []; | ||
const count = writeUnsignedVarint(n, arr, 0); | ||
expect(count).toBe(arr.length); | ||
expect(unsignedVarintByteLength(n)).toBe(count); | ||
} | ||
}); | ||
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test("RangeError", () => { | ||
const arr = []; | ||
expect(writeUnsignedVarint(300, arr, 0)).toBe(2); | ||
expect(arr).toEqual([172, 2]); | ||
arr.pop(); | ||
expect(() => { | ||
readUnsignedVarint(arr, 0); | ||
}).toThrowErrorMatchingInlineSnapshot(`"Could not decode varint"`); | ||
}); | ||
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function randint(range: number): number { | ||
return Math.floor(Math.random() * range); | ||
} |
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const N1 = 2 ** 7; | ||
const N2 = 2 ** 14; | ||
const N3 = 2 ** 21; | ||
const N4 = 2 ** 28; | ||
const N5 = 2 ** 35; | ||
const N6 = 2 ** 42; | ||
const N7 = 2 ** 49; | ||
const N8 = 2 ** 56; | ||
const N9 = 2 ** 63; | ||
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const MSB = 0x80; | ||
const REST = 0x7f; | ||
const MSBALL = ~REST; | ||
const INT = 2 ** 31; | ||
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// const U32_MAX = 0xffffffff; | ||
// const I32_MAX = 0x7fffffff; | ||
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export function unsignedVarintByteLength(value: number): number { | ||
return value < N1 | ||
? 1 | ||
: value < N2 | ||
? 2 | ||
: value < N3 | ||
? 3 | ||
: value < N4 | ||
? 4 | ||
: value < N5 | ||
? 5 | ||
: value < N6 | ||
? 6 | ||
: value < N7 | ||
? 7 | ||
: value < N8 | ||
? 8 | ||
: value < N9 | ||
? 9 | ||
: 10; | ||
} | ||
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export function writeUnsignedVarint(value: number, target: Buffer | Uint8Array | number[], offset: number): number { | ||
let i = offset; | ||
while (value >= INT) { | ||
target[i++] = (value & 0xff) | MSB; | ||
value /= 128; | ||
} | ||
while (value & MSBALL) { | ||
target[i++] = (value & 0xff) | MSB; | ||
value >>>= 7; | ||
} | ||
target[i] = value | 0; | ||
return i - offset + 1; | ||
} | ||
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export interface ReadRecord { | ||
length: number; | ||
value: number; | ||
} | ||
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export function readUnsignedVarint(data: Buffer | Uint8Array | number[], offset: number): ReadRecord { | ||
let value = 0; | ||
let shift = 0; | ||
let i = offset; | ||
let b = 0; | ||
do { | ||
if (i >= data.length) { | ||
throw new RangeError("Could not decode varint"); | ||
} | ||
b = data[i++]; | ||
value += shift < 28 ? (b & REST) << shift : (b & REST) * 2 ** shift; | ||
shift += 7; | ||
} while (b >= MSB); | ||
return { length: i - offset, value }; | ||
} | ||
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export function signedVarintByteLength(value: number): number { | ||
return unsignedVarintByteLength(value >= 0 ? value * 2 : value * -2 - 1); | ||
} | ||
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export function writeSignedVarint(value: number, target: Buffer | number[], offset: number): number { | ||
return writeUnsignedVarint(value >= 0 ? value * 2 : value * -2 - 1, target, offset); | ||
} | ||
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export function readSignedVarint(data: Buffer | number[], offset: number): ReadRecord { | ||
let { length, value } = readUnsignedVarint(data, offset); | ||
value = value & 1 ? (value + 1) / -2 : value / 2; | ||
return { length, value }; | ||
} |
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{ | ||
"extends": "../../tsconfig.build.json", | ||
"include": ["src/**/*"], | ||
"compilerOptions": { | ||
"outDir": "./build" | ||
} | ||
} |
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{ | ||
"extends": "../../tsconfig.json", | ||
"include": ["src/**/*"] | ||
} |