index.js

var OPS = require("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
};