Table of Contents

lcg_value Description

Comparison of two methods of generating random decimals from 0 to 1

1. Execution time comparison

2. Random effect comparison

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Comparison of the effects of php lcg_value and mt_rand generating random decimals from 0 to 1

Jun 20, 2018 pm 06:04 PM

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Because I need to use php to generate 0~1 random decimals for my work, I wrote an article before "php method to generate 0~1 random decimals", based on mt_rand() and mt_getrandmax()accomplish.

Later some netizens commented that the PHP native method lcg_value() can generate random decimals from 0 to 1.

lcg_value Description

float lcg_value ( void )

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lcg_value() returns a pseudo-random number in the range (0, 1). This function combines two congruential generators with periods 2^31 - 85 and 2^31 - 249. The period of this function is equal to the product of these two prime numbers.

Return: pseudo-random number in the range (0, 1).

<?phpfor ($i=0; $i<5; $i++){    echo lcg_value().PHP_EOL;
}?>

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Output:

0.11516515851995
0.064684551575297
0.68275174031189
0.55730746529099
0.70215008878091

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Comparison of two methods of generating random decimals from 0 to 1

1. Execution time comparison

The running time of executing 100,000 times based on mt_rand() and mt_getrandmax() algorithms

<?php/**
 * 生成0~1随机小数
 * @param  Int   $min
 * @param  Int   $max
 * @return Float
 */function randFloat($min=0, $max=1){
    return $min + mt_rand()/mt_getrandmax() * ($max-$min);
}// 获取microtimefunction get_microtime(){
    list($usec, $sec) = explode(&#39; &#39;, microtime());    return (float)$usec + (float)$sec;
}// 记录开始时间$starttime = get_microtime();// 执行10万次获取随机小数for($i=0; $i<100000; $i++){
    randFloat();
}// 记录结束时间$endtime = get_microtime();// 输出运行时间printf("run time %f ms\r\n", ($endtime-$starttime)*1000);?>

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Output: run time 266.893148 ms

Running time of executing lcg_value() 100,000 times

<?php// 获取microtimefunction get_microtime(){
    list($usec, $sec) = explode(&#39; &#39;, microtime());    return (float)$usec + (float)$sec;
}// 记录开始时间$starttime = get_microtime();// 执行10万次获取随机小数for($i=0; $i<100000; $i++){
    lcg_value();
}// 记录结束时间$endtime = get_microtime();// 输出运行时间printf("run time %f ms\r\n", ($endtime-$starttime)*1000);?>

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Output: run time 86.178064 ms

Execution time comparison, because lcg_value() is directly a native PHP method, and mt_rand() and mt_getrandmax() need to call two methods and need to be calculated, so The execution time of lcg_value() is about 3 times faster.

2. Random effect comparison

Random effect based on mt_rand() and mt_getrandmax() algorithms

<?php/**
 * 生成0~1随机小数
 * @param  Int   $min
 * @param  Int   $max
 * @return Float
 */function randFloat($min=0, $max=1){
    return $min + mt_rand()/mt_getrandmax() * ($max-$min);
}

header(&#39;content-type: image/png&#39;);$im = imagecreatetruecolor(512, 512);$color1 = imagecolorallocate($im, 255, 255, 255);$color2 = imagecolorallocate($im, 0, 0, 0);for($y=0; $y<512; $y++){    for($x=0; $x<512; $x++){        $rand = randFloat();        if(round($rand,2)>=0.5){
            imagesetpixel($im, $x, $y, $color1);
        }else{
            imagesetpixel($im, $x, $y, $color2);
        }
    }
}
imagepng($im);
imagedestroy($im);?>

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Random effect diagram:

Comparison of the effects of php lcg_value and mt_rand generating random decimals from 0 to 1

##Random effect of lcg_value()

<?phpheader(&#39;content-type: image/png&#39;);$im = imagecreatetruecolor(512, 512);$color1 = imagecolorallocate($im, 255, 255, 255);$color2 = imagecolorallocate($im, 0, 0, 0);for($y=0; $y<512; $y++){    for($x=0; $x<512; $x++){        $rand = lcg_value();        if(round($rand,2)>=0.5){
            imagesetpixel($im, $x, $y, $color1);
        }else{
            imagesetpixel($im, $x, $y, $color2);
        }
    }
}
imagepng($im);
imagedestroy($im);?>

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Random effect diagram:

Comparison of the effects of php lcg_value and mt_rand generating random decimals from 0 to 1

Comparing the random effects, it can be seen that using mt_rand() and mt_getrandmax( ) algorithm generates random effects that are out of order, and the random effects are better than lcg_value().
This article explains the comparison of the effects of generating 0~1 random decimals between php lcg_value and mt_rand. For more related content, please pay attention to the php Chinese website.

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