Random\Randomizer::nextFloat
(PHP 8 >= 8.3.0)
Random\Randomizer::nextFloat — Get a float from the right-open interval [0.0, 1.0)
说明
Returns a uniformly selected, equidistributed float from the right-open
interval from 0.0 until, but not including,
1.0.
The chance for returned float to be within a given right-open sub-interval
is proportional to the size of the sub-interval.
This means that the chance for a float to be less than 0.5
is 50 %, which is equal to the chance for a float to be at least 0.5.
Likewise the chance for a float to be within the right-open interval from
0.2 until, but not including, 0.25 is
exactly 5 %.
This property makes it easy to leverage Random\Randomizer::nextFloat() to generate a random boolean with a given chance by checking if the returned float is less than a given chance.
注意:
The domain of the returnable floats of Random\Randomizer::nextFloat() is identical to that of
Randomizer::getFloat(0.0, 1.0, IntervalBoundary::ClosedOpen).The internal implementation of Random\Randomizer::nextFloat() is more efficient.
Scaling the return value to a different interval using multiplication or addition (a so-called affine transformation) might result in a bias in the resulting value as floats are not equally dense across the number line. As not all values can be exactly represented by a float, the result of the affine transformation might also result in values outside of the requested interval due to implicit rounding. An in-depth explanation of the problems with the affine transformation is given in the documentation for Random\Randomizer::getFloat().
Use Random\Randomizer::getFloat() to generate a random float within an arbitrary interval. Use Random\Randomizer::getInt() to generate a random integer within an arbitrary interval.
参数
此函数没有参数。
返回值
A uniformly selected, equidistributed float from the right-open (IntervalBoundary::ClosedOpen)
interval [0.0, 1.0).
0.0 is a possible return value, 1.0 is not.
错误／异常
-
底层
Random\Randomizer::$engine的 Random\Engine::generate() 方法抛出的任何 Throwable。
示例
示例 #1 Random\Randomizer::nextFloat() example
<?php
$r = new \Random\Randomizer();
// The resulting bool will be true with the given chance.
$chance = 0.5;
$bool = $r->nextFloat() < $chance;
echo ($bool ? "You won" : "You lost"), "\n";
?>以上示例的输出类似于：
You won
示例 #2 Incorrect scaling using an affine transformation
<?php
final class MaxEngine implements Random\Engine {
public function generate(): string {
return "\xff";
}
}
$randomizer = new \Random\Randomizer(new MaxEngine);
$min = 3.5;
$max = 4.5;
// DO NOT DO THIS:
//
// This will output 4.5, despite nextFloat() sampling from
// a right-open interval, which will never return 1.
printf("Wrong scaling: %.17g", $randomizer->nextFloat() * ($max - $min) + $min);
// Correct:
// $randomizer->getFloat($min, $max, \Random\IntervalBoundary::ClosedOpen);
?>以上示例会输出：
Wrong scaling: 4.5
参见
- Random\Randomizer::getFloat() - Get a uniformly selected float
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