Parsing from binary (Python encoding via avro) about decimal.js

[MikeMcl]

I have no experience with avro but I read that it stores decimals using the two’s-complement representation of the unscaled integer value in big-endian byte order, so the following function should work.

It assumes that the decimals will be positive values. If not, then test the highest bit of the first byte and if it is set then invert all the bits by subtracting each byte from 256 before convertion to hex, then add one to the BigInt result.

// Must be greater or equal to 38 if you are decoding values with a precision of 38.
Decimal.precision = 40;

const bufferToDecimal = (buf, scale) => new Decimal(
  BigInt(buf.reduce((hex, byte) => hex + byte.toString(16).
  padStart(2, '0'), '0x')).toString()
).div(10 ** scale);