JIT-startsWith and endsWith #711

'use strict'

const assert = require('assert')
const Benchmark = require('benchmark')

const test = 'Lorem Ipsum I dolor'
const startsWithJit = startsWithJitGen('Lorem')
const endsWithJit = endsWithJitGen('dolor')
const Lorem = 'Lorem'
const dolor = 'dolor'

const lorem = 'lorem'
const Dolor = 'Dolor'

assert.ok(startsWithJit('ol') === false)
assert.ok(startsWithJit('or') === false)
assert.ok(startsWithJit('Dolor') === false)
assert.ok(startsWithJit('dolor') === false)
assert.ok(startsWithJit('lorem') === false)
assert.ok(startsWithJit('Lorem') === true)

assert.ok(endsWithJit('ol') === false)
assert.ok(endsWithJit('or') === false)
assert.ok(endsWithJit('Dolor') === false)
assert.ok(endsWithJit('dolor') === true)

new Benchmark.Suite()
  .add('true startsWith', function () { test.startsWith(Lorem) })
  .add('true startsWith jit', function () { startsWithJit(test) })
  .add('true endsWith', function () { test.endsWith(dolor) })
  .add('true endsWith jit', function () { endsWithJit(test) })
  .add('false startsWith', function () { test.startsWith(lorem) })
  .add('false startsWith jit', function () { startsWithJit(test) })
  .add('false endsWith', function () { test.endsWith(Dolor) })
  .add('false endsWith jit', function () { endsWithJit(test) })
  .on('cycle', function (event) { console.log(String(event.target)) })
  .run()

function startsWithJitGen(sequence) {
  const chain = []

  chain.push('(typeof value === \'string\')')
  chain.push(`(value.length >= ${sequence.length})`)

  for (let i = 0, il = sequence.length; i < il; ++i) {
    chain.push(`(value[${i}] === '${sequence[i]}')`)
  }

  const fnBody = 'return ' + chain.join(' && ')
  return new Function('value', fnBody)
}

function endsWithJitGen(sequence) {
  const chain = []

  chain.push('(typeof value === \'string\')')
  chain.push(`(value.length >= ${sequence.length})`)

  for (let i = 0, il = sequence.length; i < il; ++i) {
    if (i === 0) {
      chain.push(`(value[len] === '${sequence[i]}')`)
      continue
    }
    chain.push(`(value[len + ${i}] === '${sequence[i]}')`)
  }

  const fnBody = `const len = value.length - ${sequence.length}; return ` + chain.join(' && ')
  return new Function('value', fnBody)
}