index.js

var OPS = require('@tatumio/bitcoincash-ops')

function encodingLength (i) {
  return i < OPS.OP_PUSHDATA1 ? 1 : i <= 0xff ? 2 : i <= 0xffff ? 3 : 5
}

function encode (buffer, number, offset) {
  var size = encodingLength(number)

  // ~6 bit
  if (size === 1) {
    buffer.writeUInt8(number, offset)

    // 8 bit
  } else if (size === 2) {
    buffer.writeUInt8(OPS.OP_PUSHDATA1, offset)
    buffer.writeUInt8(number, offset + 1)

    // 16 bit
  } else if (size === 3) {
    buffer.writeUInt8(OPS.OP_PUSHDATA2, offset)
    buffer.writeUInt16LE(number, offset + 1)

    // 32 bit
  } else {
    buffer.writeUInt8(OPS.OP_PUSHDATA4, offset)
    buffer.writeUInt32LE(number, offset + 1)
  }

  return size
}

function decode (buffer, offset) {
  var opcode = buffer.readUInt8(offset)
  var number, size

  // ~6 bit
  if (opcode < OPS.OP_PUSHDATA1) {
    number = opcode
    size = 1

    // 8 bit
  } else if (opcode === OPS.OP_PUSHDATA1) {
    if (offset + 2 > buffer.length) return null
    number = buffer.readUInt8(offset + 1)
    size = 2

    // 16 bit
  } else if (opcode === OPS.OP_PUSHDATA2) {
    if (offset + 3 > buffer.length) return null
    number = buffer.readUInt16LE(offset + 1)
    size = 3

    // 32 bit
  } else {
    if (offset + 5 > buffer.length) return null
    if (opcode !== OPS.OP_PUSHDATA4) throw new Error('Unexpected opcode')

    number = buffer.readUInt32LE(offset + 1)
    size = 5
  }

  return {
    opcode: opcode,
    number: number,
    size: size
  }
}

module.exports = {
  encodingLength: encodingLength,
  encode: encode,
  decode: decode
}