@trezor/utxo-lib/lib/script/scriptNumber.js

Client-side Bitcoin-like JavaScript library

"use strict";

Object.defineProperty(exports, "__esModule", {
  value: true
});
exports.decode = decode;
exports.encode = encode;
function decode(buffer, maxLength = 4, minimal = true) {
  const {
    length
  } = buffer;
  if (length === 0) return 0;
  if (length > maxLength) throw new TypeError('Script number overflow');
  if (minimal) {
    if ((buffer[length - 1] & 0x7f) === 0) {
      if (length <= 1 || (buffer[length - 2] & 0x80) === 0) throw new Error('Non-minimally encoded script number');
    }
  }
  if (length === 5) {
    const a = buffer.readUInt32LE(0);
    const b = buffer.readUInt8(4);
    if (b & 0x80) return -((b & ~0x80) * 0x100000000 + a);
    return b * 0x100000000 + a;
  }
  let result = 0;
  for (let i = 0; i < length; ++i) {
    result |= buffer[i] << 8 * i;
  }
  if (buffer[length - 1] & 0x80) return -(result & ~(0x80 << 8 * (length - 1)));
  return result;
}
function scriptNumSize(i) {
  if (i > 0x7fffffff) return 5;
  if (i > 0x7fffff) return 4;
  if (i > 0x7fff) return 3;
  if (i > 0x7f) return 2;
  if (i > 0x00) return 1;
  return 0;
}
function encode(number) {
  let value = Math.abs(number);
  const size = scriptNumSize(value);
  const buffer = Buffer.allocUnsafe(size);
  const negative = number < 0;
  for (let i = 0; i < size; ++i) {
    buffer.writeUInt8(value & 0xff, i);
    value >>= 8;
  }
  if (buffer[size - 1] & 0x80) {
    buffer.writeUInt8(negative ? 0x80 : 0x00, size - 1);
  } else if (negative) {
    buffer[size - 1] |= 0x80;
  }
  return buffer;
}
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