PHP's log1p in TypeScript

How to use

Install via yarn add locutus and import: import { log1p } from 'locutus/php/math/log1p'.

Or with CommonJS: const { log1p } = require('locutus/php/math/log1p')

Use a bundler that supports tree-shaking so you only ship the functions you actually use. Vite, webpack, Rollup, and Parcel all handle this. For server-side use this is less of a concern.

Examples

These examples are extracted from test cases that automatically verify our functions against their native counterparts.

#	code	expected result
1	log1p(1e-15)	9.999999999999995e-16

Notes

• Precision ‘n’ can be adjusted as desired

Here's what our current TypeScript equivalent to PHP's log1p looks like.

TSTypeScript JSJavaScript TSStandalone TS JSStandalone JS

Copy code

export function log1p(x: number): number | string {
  //      discuss at: https://locutus.io/php/log1p/
  // parity verified: PHP 8.3
  //     original by: Brett Zamir (https://brett-zamir.me)
  //     improved by: Robert Eisele (https://www.xarg.org/)
  //          note 1: Precision 'n' can be adjusted as desired
  //       example 1: log1p(1e-15)
  //       returns 1: 9.999999999999995e-16

  let ret = 0
  // degree of precision
  const n = 50

  if (x <= -1) {
    // JavaScript style would be to return Number.NEGATIVE_INFINITY
    return '-INF'
  }
  if (x < 0 || x > 1) {
    return Math.log(1 + x)
  }
  for (let i = 1; i < n; i++) {
    ret += Math.pow(-x, i) / i
  }

  return -ret
}

export function log1p(x) {
  //      discuss at: https://locutus.io/php/log1p/
  // parity verified: PHP 8.3
  //     original by: Brett Zamir (https://brett-zamir.me)
  //     improved by: Robert Eisele (https://www.xarg.org/)
  //          note 1: Precision 'n' can be adjusted as desired
  //       example 1: log1p(1e-15)
  //       returns 1: 9.999999999999995e-16

  let ret = 0
  // degree of precision
  const n = 50

  if (x <= -1) {
    // JavaScript style would be to return Number.NEGATIVE_INFINITY
    return '-INF'
  }
  if (x < 0 || x > 1) {
    return Math.log(1 + x)
  }
  for (let i = 1; i < n; i++) {
    ret += Math.pow(-x, i) / i
  }

  return -ret
}

Improve this function

Locutus is a community effort following The McDonald's Theory: we ship first iterations, hoping others will improve them. If you see something that could be better, we'd love your contribution.

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