node-mysql2 parseFloat benchmarking

parse-float.js

#! /usr/bin/env node
'use strict';

const minus = '-'.charCodeAt(0);
const plus = '+'.charCodeAt(0);
// TODO: handle E notation
const dot = '.'.charCodeAt(0);
const exponent = 'e'.charCodeAt(0);
const exponentCapital = 'E'.charCodeAt(0);

function parseFloatOld(len) {
    if (len === null) {
      return null;
    }
    let result = 0;
    const end = this.offset + len;
    let factor = 1;
    let pastDot = false;
    let charCode = 0;
    if (len === 0) {
      return 0; // TODO: assert? exception?
    }
    if (this.buffer[this.offset] === minus) {
      this.offset++;
      factor = -1;
    }
    if (this.buffer[this.offset] === plus) {
      this.offset++; // just ignore
    }
    while (this.offset < end) {
      charCode = this.buffer[this.offset];
      if (charCode === dot) {
        pastDot = true;
        this.offset++;
      } else if (charCode === exponent || charCode === exponentCapital) {
        this.offset++;
        const exponentValue = parseInt(end - this.offset);
        return (result / factor) * Math.pow(10, exponentValue);
      } else {
        result *= 10;
        result += this.buffer[this.offset] - 48;
        this.offset++;
        if (pastDot) {
          factor = factor * 10;
        }
      }
    }
    return result / factor;
  }

const _parseFloat = global.parseFloat;
function parseFloatNew(len)
{
  const ret = _parseFloat(this.buffer.slice(this.offset, this.offset + len).toString('ascii'));
  this.offset += len;
  return ret;
}    


function Float()
{
  this.offset = 0;
  this.buffer = Buffer.from([ 48, 46, 52, 53, 52, 57, 52, 50, 53, 51, 56, 52, 51, 49, 49, 57, 48, 48, 52 ]);
}
Float.prototype.parseFloatOld = parseFloatOld;
Float.prototype.parseFloatNew = parseFloatNew;
  
const num = new Float();

console.log(Array.from(num.buffer.map((c) => String.fromCharCode(c))));
num.offset = 0;
const a = num.parseFloatOld(19)
console.log(a);

num.offset = 0;
const b = num.parseFloatNew(19);
console.log(b);

measure('old', () => { num.offset = 0; void num.parseFloatOld(19); });
measure('new', () => { num.offset = 0; void num.parseFloatNew(19); });

function measure(label, fun, howMany = 1000000)
{
  fun();
  fun();
  fun();
  
  const start = Date.now();
  for (let i=0; i < howMany; i++)
    fun();
  const end = Date.now();

  console.log(label, ':', (end-start) + 'ms');
}