unfuck/src/optimisers/multiplication.js

A brainfuck to Javascript compiler with optimizations.

function checkForLeftPattern (ast) {
  var first = ast[0].is === 'RELSFT';
  first = first && ast[0].body.move === 0;
  first = first && ast[0].body.value === -1;

  var tail = ast.slice(1).map((ins) => {
    var out = ins.is === 'RELSFT';
    out = out && ins.body.move !== 0;
    out = out && ins.body.value > 0;
    return out;
  })

  return first && (tail.reduce((acc, res) => acc && res, true));
}

function checkForRightPattern (ast) {
  var head = ast.slice(0,-1).map((ins) => {
    var out = ins.is === 'RELSFT';
    out = out && ins.body.move !== 0;
    out = out && ins.body.value > 0;
    return out;
  })

  var last = ast.slice(-1)[0].is === 'RELSFT';
  last = last && ast.slice(-1)[0].body.move === 0;
  last = last && ast.slice(-1)[0].body.value === -1;

  return last && (head.reduce((acc, res) => acc && res, true));
}

function makeMul (ast, direction) {
  var slice = (direction === 'left' ? ast.slice(1) : (direction === 'right' ? ast.slice(0, -1) : []));
  var factors = slice.reduce((acc, ins) => {
    acc.push({
      move: ins.body.move,
      factor: ins.body.value
    })
    return acc;
  }, [])

  return {
    is: 'MUL',
    body: {
      factors
    }
  }
}

function multiplication ( settings, ast ) {
  return ast.reduce((acc, ins) => {
    if (ins.is === 'IF') {
      if (checkForLeftPattern(ins.body)) {
        acc.push(makeMul(ins.body, 'left'));
      } else if (checkForRightPattern(ins.body)) {
        acc.push(makeMul(ins.body, 'right'));
      } else {
        ins.body = multiplication(settings, ins.body);
        acc.push(ins);
      }
    } else {
      acc.push(ins);
    }
    return acc;
  }, [])
}

module.exports = multiplication;