README

A PHP library that provides a port of Java's Math.nextAfter() family of functions.

Overview

This library implements IEEE 754 floating-point manipulation functions that return the next representable floating-point number in a given direction:

• nextAfter($x, $y) - Returns the adjacent float in the direction of another value
• nextUp($x) - Returns the next float toward positive infinity
• nextDown($x) - Returns the next float toward negative infinity

Requirements

• PHP 8.4 or higher
• Little-endian 64-bit integers
• IEEE 754 double-precision floats (binary64)

The library performs runtime assertions to verify these constraints are met on the current system.

Installation

$ composer require nsfisis/next-after

Exapmles

use Nsfisis\NextAfter\NextAfter;

// Get the next representable float after 1.0.
$next = NextAfter::nextAfter(1.0, 2.0); // => 1.0000000000000002

// Get the next float toward positive infinity.
$up = NextAfter::nextUp(1.0); // => 1.0000000000000002

// Get the next float toward negative infinity.
$down = NextAfter::nextDown(1.0); // => 0.9999999999999999

API Reference

nextAfter(float $x, float $y): float

Returns the floating-point number adjacent to $x in the direction of $y. If $x equals y, returns y.

Special Cases

• If either argument is NaN, the result is NaN
• If both arguments equal, $y is returned as it is
• If $x is minValue() and $y is greater than $x, the result is positive zero
• If $x is -minValue() and $y is less than $x, the result is negative zero
• If $x is infinity and $y is not, PHP_FLOAT_MAX is returned
• If $x is negative infinity and $y is not, -PHP_FLOAT_MAX is returned
• If $x is PHP_FLOAT_MAX and $y is infinity, infinity is returned
• If $x is -PHP_FLOAT_MAX and $y is negative infinity, negative infinity is returned

nextUp(float $x): float

Returns the floating-point number adjacent to $x in the direction of positive infinity.

This is semantically equivalent to nextAfter($x, INF).

Special Cases

• If $x is NaN, the result is NaN
• If $x is positive infinity, the result is positive infinity
• If $x is zero, the result is minValue()
• If $x is -minValue(), the result is negative zero
• If $x is PHP_FLOAT_MAX, infinity is returned

nextDown(float $x): float

Returns the floating-point number adjacent to $x in the direction of negative infinity.

This is semantically equivalent to nextAfter($x, -INF).

Special Cases

• If $x is NaN, the result is NaN
• If $x is negative infinity, the result is negative infinity
• If $x is zero, the result is -minValue()
• If $x is minValue(), the result is positive zero
• If $x is -PHP_FLOAT_MAX, negative infinity is returned

minValue(): float

Returns the minimum representable non-zero floating-point number. Note that this is a subnormal number and is not the same as PHP_FLOAT_MIN, which is the smallest normal number.

License

See the LICENSE file.

Credits

This library is a PHP port of Java's java.lang.Math.nextAfter(), nextUp(), and nextDown() methods.

Reference: Java Math Documentation