index.js

// get a number modulo PI2 (taking care of negatives)
const PI = Math.PI
const PI2 = 2 * Math.PI
function phmod (ph) { return ph < 0 ? PI2 + (ph % PI2) : ph % PI2 }

/**
 * Perform a phase-unwrapping of a phase data
 * @param {Array} input - phase data
 * @param {Array} output - (Optional) the output array to store the unrapped
 * phase data. If not provided, an in-place modification is performed.
 * If true is passed as an argument, a new array is created.
 * @return {Array} the unrapped phase data
 *
 * @example
 * // given a phase data of a spectrum...
 * const unwrap = require('unwrap-phases')
 * unwrap(phases) // in-place unwrapping
 * const unwrapped = unwrap(phases, true) // new output array
 */
function unwrap (input, output) {
  const size = input.length
  if (!output) output = input
  if (output === true) output = new Array(size)

  let shift = 0
  let prev = phmod(input[0])
  output[0] = prev
  for (let i = 1; i < size; i++) {
    const current = phmod(input[i])
    const diff = current - prev
    if (diff < -PI) shift += PI2
    else if (diff > PI) shift -= PI2
    output[i] = current + shift
    prev = current
  }
  return output
}

module.exports = unwrap