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0cfc45b667
* random: Add `max_offset` local to Randomizer::getBytesFromString() * random: Use branchless implementation for mask generation in Randomizer::getBytesFromString() This was benchmarked against clzl with a standalone script with random inputs and is slightly faster. clzl requires an additional branch to handle the source_length = 1 / max_offset = 0 case. * Improve comment for masking in Randomizer::getBytesFromString()
162 lines
2.9 KiB
PHP
162 lines
2.9 KiB
PHP
--TEST--
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Random: Randomizer: getBytesFromString(): Fast Path Masking
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--FILE--
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<?php
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use Random\Engine\Test\TestWrapperEngine;
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use Random\Engine\Xoshiro256StarStar;
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use Random\Randomizer;
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require __DIR__ . "/../../engines.inc";
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$allBytes = implode('', array_map(
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fn ($byte) => chr($byte),
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range(0x00, 0xff)
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));
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// Xoshiro256** is the fastest engine available.
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$xoshiro = new Xoshiro256StarStar();
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var_dump(strlen($allBytes));
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echo PHP_EOL;
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// Fast path: Inputs less than or equal to 256.
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for ($i = 1; $i <= strlen($allBytes); $i *= 2) {
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echo "{$i}:", PHP_EOL;
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$wrapper = new TestWrapperEngine($xoshiro);
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$r = new Randomizer($wrapper);
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$result = $r->getBytesFromString(substr($allBytes, 0, $i), 20000);
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// Xoshiro256** is a 64 Bit engine and thus generates 8 bytes at once.
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// For powers of two we expect no rejections and thus exactly
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// 20000/8 = 2500 calls to the engine.
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var_dump($wrapper->getCount());
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$count = [];
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for ($j = 0; $j < strlen($result); $j++) {
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$b = $result[$j];
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$count[ord($b)] ??= 0;
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$count[ord($b)]++;
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}
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// We also expect that each possible value appears at least once, if
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// not is is very likely that some bits were erroneously masked away.
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var_dump(count($count));
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echo PHP_EOL;
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}
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// Test lengths that are one more than the powers of two. For these
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// the maximum offset will be a power of two and thus a minimal number
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// of bits will be set in the offset.
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for ($i = 1; ($i + 1) <= strlen($allBytes); $i *= 2) {
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$oneMore = $i + 1;
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echo "{$oneMore}:", PHP_EOL;
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$wrapper = new TestWrapperEngine($xoshiro);
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$r = new Randomizer($wrapper);
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$result = $r->getBytesFromString(substr($allBytes, 0, $oneMore), 20000);
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$count = [];
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for ($j = 0; $j < strlen($result); $j++) {
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$b = $result[$j];
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$count[ord($b)] ??= 0;
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$count[ord($b)]++;
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}
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// We expect that each possible value appears at least once, if
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// not is is very likely that some bits were erroneously masked away.
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var_dump(count($count));
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echo PHP_EOL;
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}
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echo "Slow Path:", PHP_EOL;
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$wrapper = new TestWrapperEngine($xoshiro);
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$r = new Randomizer($wrapper);
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$result = $r->getBytesFromString($allBytes . $allBytes, 20000);
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// In the slow path we expect one call per byte, i.e. 20000
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var_dump($wrapper->getCount());
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$count = [];
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for ($j = 0; $j < strlen($result); $j++) {
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$b = $result[$j];
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$count[ord($b)] ??= 0;
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$count[ord($b)]++;
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}
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// We also expect that each possible value appears at least once, if
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// not is is very likely that some bits were erroneously masked away.
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var_dump(count($count));
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?>
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--EXPECT--
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int(256)
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1:
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int(2500)
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int(1)
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2:
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int(2500)
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int(2)
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4:
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int(2500)
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int(4)
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8:
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int(2500)
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int(8)
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16:
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int(2500)
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int(16)
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32:
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int(2500)
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int(32)
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64:
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int(2500)
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int(64)
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128:
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int(2500)
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int(128)
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256:
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int(2500)
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int(256)
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2:
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int(2)
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3:
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int(3)
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5:
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int(5)
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9:
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int(9)
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17:
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int(17)
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33:
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int(33)
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65:
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int(65)
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129:
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int(129)
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Slow Path:
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int(20000)
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int(256)
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