<?php namespace App\Util\Blurhash; final class AC { public static function encode(array $value, float $max_value): float { $quant_r = static::quantise($value[0] / $max_value); $quant_g = static::quantise($value[1] / $max_value); $quant_b = static::quantise($value[2] / $max_value); return $quant_r * 19 * 19 + $quant_g * 19 + $quant_b; } public static function decode(int $value, float $max_value): array { $quant_r = floor($value / (19 * 19)); $quant_g = floor($value / 19) % 19; $quant_b = $value % 19; return [ static::signPow(($quant_r - 9) / 9, 2) * $max_value, static::signPow(($quant_g - 9) / 9, 2) * $max_value, static::signPow(($quant_b - 9) / 9, 2) * $max_value ]; } private static function quantise(float $value): float { return floor(max(0, min(18, floor(static::signPow($value, 0.5) * 9 + 9.5)))); } private static function signPow(float $base, float $exp): float { $sign = $base <=> 0; return $sign * pow(abs($base), $exp); } }