tough-rational/lib/functions/gcd.js

Rational class using BigInt with fallback to bignumber.js

'use strict';

const abs = require('./abs');
const min = require('../min');
const roughLOB = require('./rough-lob');
const util = require('../util');
const mapToNegative = util.map((v) => -v);

const greatestCommonDenominator = (a, b) => {
  a = abs.absNonCoerced(a);
  b = abs.absNonCoerced(b);
  if (a === b) return a;
  if (a === BigInt(0)) return b;
  if (b === BigInt(0)) return a;
  var c = BigInt(1), d, t;
  while (a % BigInt(2) === BigInt(0) && b % BigInt(2) === BigInt(0)) {
    d = min(roughLOB(a), roughLOB(b));
    a /= d;
    b /= d;
    c *= d;
  }
  while (a % BigInt(2) === BigInt(0)) {
    a /= roughLOB(a);
  }
  do {
    while (b % BigInt(2) === BigInt(0)) {
      b /= roughLOB(b);
    }
    if (a > b) {
      t = b; b = a; a = t;
    }
    b -= a;
  } while (b !== BigInt(0));
  return abs.absNonCoerced(c) === BigInt(1) ? a : a * c;
}

const gcdReduce = ([ a, b ]) => {
  const greatest = greatestCommonDenominator(a, b);
  const retval = [ a / greatest, b / greatest ];
  if (retval[0] < BigInt(0) && retval[1] < BigInt(0)) return mapToNegative(retval);
  return retval; 
};

Object.assign(module.exports, {
  greatestCommonDenominator,
  gcdReduce
});