71 lines
1.7 KiB
PHP
71 lines
1.7 KiB
PHP
<?php
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declare(strict_types=1);
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namespace ZxcvbnPhp\Math;
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use ZxcvbnPhp\Math\Impl\BinomialProviderPhp73Gmp;
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use ZxcvbnPhp\Math\Impl\BinomialProviderFloat64;
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use ZxcvbnPhp\Math\Impl\BinomialProviderInt64;
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class Binomial
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{
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private static $provider = null;
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private function __construct()
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{
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throw new \LogicException(__CLASS__ . " is static");
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}
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/**
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* Calculate binomial coefficient (n choose k).
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*
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* @param int $n
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* @param int $k
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* @return float
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*/
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public static function binom(int $n, int $k): float
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{
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return self::getProvider()->binom($n, $k);
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}
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public static function getProvider(): BinomialProvider
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{
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if (self::$provider === null) {
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self::$provider = self::initProvider();
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}
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return self::$provider;
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}
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/**
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* @return string[]
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*/
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public static function getUsableProviderClasses(): array
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{
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// In order of priority. The first provider with a value of true will be used.
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$possibleProviderClasses = [
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BinomialProviderPhp73Gmp::class => function_exists('gmp_binomial'),
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BinomialProviderInt64::class => PHP_INT_SIZE >= 8,
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BinomialProviderFloat64::class => PHP_FLOAT_DIG >= 15,
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];
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$possibleProviderClasses = array_filter($possibleProviderClasses);
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return array_keys($possibleProviderClasses);
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}
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private static function initProvider(): BinomialProvider
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{
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$providerClasses = self::getUsableProviderClasses();
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if (!$providerClasses) {
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throw new \LogicException("No valid providers");
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}
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$bestProviderClass = reset($providerClasses);
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return new $bestProviderClass();
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}
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}
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