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