Function getFastValue

src/parseTools.mjs:563–613

(a, op, b)

// Given two values and an operation, returns the result of that operation.
// Tries to do as much as possible at compile time.
function getFastValue(a, op, b) {
  // In the past we supported many operations, but today we only use addition.
  assert(op == '+');

  // Convert 'true' and 'false' to '1' and '0'.
  a = a === 'true' ? '1' : a === 'false' ? '0' : a;
  b = b === 'true' ? '1' : b === 'false' ? '0' : b;

  let aNumber = null;
  let bNumber = null;
  if (typeof a == 'number') {
    aNumber = a;
    a = a.toString();
  } else if (isNumber(a)) {
    aNumber = parseFloat(a);
  }
  if (typeof b == 'number') {
    bNumber = b;
    b = b.toString();
  } else if (isNumber(b)) {
    bNumber = parseFloat(b);
  }

  // First check if we can do the addition at compile time
  if (aNumber !== null && bNumber !== null) {
    return (aNumber + bNumber).toString();
  }

  // If one of them is a number, keep it last
  if (aNumber !== null) {
    const c = b;
    b = a;
    a = c;
    const cNumber = bNumber;
    bNumber = aNumber;
    aNumber = cNumber;
  }

  if (aNumber === 0) {
    return b;
  } else if (bNumber === 0) {
    return a;
  }

  if (b[0] === '-') {
    op = '-';
    b = b.slice(1);
  }

  return `(${a})${op}(${b})`;
}

function calcFastOffset(ptr, pos) {
  return getFastValue(ptr, '+', pos);