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React-native bigint64 deserialization problem - refactoring/bigint64le #16

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React-native bigint64 deserialization problem - refactoring/bigint64le #16

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89928fb
React-native compatible big int deserialization
Admdebian Nov 29, 2021
5377e05
byte lenght bugfix
Admdebian Nov 29, 2021
a0f706d
Custom deserialization function for 8 bit buffers
Admdebian Nov 29, 2021
372cef9
lint and comment fix
Admdebian Nov 29, 2021
78b1e2b
number to bigint refactoring and small changes
Admdebian Nov 29, 2021
3e53b69
fix test failure: The number NaN cannot be converted to a BigInt
Admdebian Nov 29, 2021
0f9e287
Bugfix for long buffers
Admdebian Nov 29, 2021
a2dce11
Minimal changes to work with react-native
Admdebian Nov 29, 2021
e7374a8
Fix signed numbers without << operator
Admdebian Nov 29, 2021
1eba710
Problem with biginteger and BigInteger
Admdebian Dec 9, 2021
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57 changes: 33 additions & 24 deletions src/readBig.ts
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Original file line number Diff line number Diff line change
@@ -1,5 +1,3 @@
import { Buffer } from 'buffer'

// https://github.com/nodejs/node/blob/v14.17.0/lib/internal/errors.js#L758
const ERR_BUFFER_OUT_OF_BOUNDS = () => new Error('Attempt to access memory outside buffer bounds')

Expand Down Expand Up @@ -28,30 +26,41 @@ function boundsError(value: number, length: number) {
throw ERR_OUT_OF_RANGE('offset', `>= 0 and <= ${length}`, value)
}

// https://github.com/nodejs/node/blob/v14.17.0/lib/internal/buffer.js#L129-L145
export function readBigInt64LE(buffer: Buffer, offset = 0): bigint {
validateNumber(offset, 'offset')
const first = buffer[offset]
const last = buffer[offset + 7]
if (first === undefined || last === undefined) boundsError(offset, buffer.length - 8)
// tslint:disable-next-line:no-bitwise
const val = buffer[offset + 4] + buffer[offset + 5] * 2 ** 8 + buffer[offset + 6] * 2 ** 16 + (last << 24) // Overflow
return (
(BigInt(val) << BigInt(32)) + // tslint:disable-line:no-bitwise
BigInt(first + buffer[++offset] * 2 ** 8 + buffer[++offset] * 2 ** 16 + buffer[++offset] * 2 ** 24)
)
}

// https://github.com/nodejs/node/blob/v14.17.0/lib/internal/buffer.js#L89-L107
// This function works with react-native >= 0.66.1
export function readBigUInt64LE(buffer: Buffer, offset = 0): bigint {
validateNumber(offset, 'offset')
const first = buffer[offset]
const last = buffer[offset + 7]
if (first === undefined || last === undefined) boundsError(offset, buffer.length - 8)
buffer = buffer.slice(offset)

const bufferLenght = Math.min(buffer.length, 8)
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typo in the name. also, i believe this code expects buffer to have 8 bytes storing the number, so you can get rid of the min here and also the Number.MAX_VALUE / maxIndex check below.


let tot: number = 0
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I think this code loses precision -- this is a floating point number, which has fewer bits of precision than a 64 bit integer (since some of its 64 bits are allocated to the exponent). I think if you make this a BigInt right off the bat, it should be fine.

const maxIndex = Math.log2(Number.MAX_VALUE)
for(let index = 0; index < bufferLenght; index++) {
const value = buffer[index]
const exponent = 8*index

if(exponent > maxIndex)
throw new Error("out of range")

const lo = first + buffer[++offset] * 2 ** 8 + buffer[++offset] * 2 ** 16 + buffer[++offset] * 2 ** 24
const addend = value * Math.pow(2, exponent)

tot += addend

const hi = buffer[++offset] + buffer[++offset] * 2 ** 8 + buffer[++offset] * 2 ** 16 + last * 2 ** 24
// console.log("index: " + index + ", buffer value: " + value + ", decimal value: " + addend + ", tot: " + tot)
}

return BigInt(lo) + (BigInt(hi) << BigInt(32)) // tslint:disable-line:no-bitwise
return BigInt(tot)
}

// This function works with react-native >= 0.66.1
export function readBigInt64LE(buffer: Buffer, offset = 0): bigint {
const resultUnsigned = readBigUInt64LE(buffer, offset)

const FFFFFFFFFFFFFFFF = BigInt(2**64 - 1);

if(buffer.length >= 8) {
if(buffer[7] >= 128)
return resultUnsigned - FFFFFFFFFFFFFFFF;
}

return resultUnsigned
}