Comparison of the effects of PHP lcg_value and Mt_rand on generating 0~1 random decimals

Because work requires PHP to generate 0~1 random decimals, previously wrote a "PHP generation 0~1 Random Decimal method", based on Mt_rand ()And Mt_getrandmax ()Realize.

Later, a netizen commented that php native method lcg_value () can realize 0~1 random decimal generation.

Lcg_value description

float Lcg_value (void)

Lcg_value () returns a pseudo-random number with a range of (0, 1). This function combines two co-generators with a period of 2^31-85 and 2^31-249. The period of this function is equal to the product of the two primes.

Returns: the pseudo-random number of the range (0, 1).

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

Output:

0.115165158519950.0646845515752970.682751740311890.557307465290990.70215008878091

Comparison of two generation 0~1 random decimal methods

1. Execution Time Comparison

Executes 100,000 times based on the Mt_rand () and Mt_getrandmax () algorithm run time

<?php/** * Generate 0~1 random decimals * @param  int   $min * @param  int   $max * @return Float */function randfloat ($min = 0, $ Max=1) {    return $min + Mt_rand ()/mt_getrandmax () * ($max-$min);} Get Microtimefunction Get_microtime () {    list ($usec, $sec) = explode (' ', Microtime ());    return (float) $usec + (float) $sec;} Record start Time $starttime = Get_microtime ();//execute 100,000 times to get random decimals for ($i =0; $i <100000; $i + +) {    randfloat ();} Record end Time $endtime = Get_microtime ();//Output Runtime printf ("Run time%f ms\r\n", ($endtime-$starttime) *1000);? >

Output: Run time 266.893148 Ms

Run time of Lcg_value () 100,000 times

<?php//get Microtimefunction get_microtime () {    list ($usec, $sec) = Explode ("', Microtime ());    return (float) $usec + (float) $sec;} Record start Time $starttime = Get_microtime ();//execute 100,000 times to get random decimals for ($i =0; $i <100000; $i + +) {    lcg_value ();} Record end Time $endtime = Get_microtime ();//Output Runtime printf ("Run time%f ms\r\n", ($endtime-$starttime) *1000);? >

Output: Run time 86.178064 Ms

Execution time comparison, because Lcg_value () is directly php native method, while Mt_rand () and Mt_getrandmax () need to call two methods, and need to calculate, so Lcg_value () execution time is about 3 times times faster.

2. Comparison of random effects

Random effects based on the Mt_rand () and Mt_getrandmax () algorithms

<?php/** * Generate 0~1 random decimals * @param  int   $min * @param  int   $max * @return Float */function randfloat ($min = 0, $ Max=1) {    return $min + Mt_rand ()/mt_getrandmax () * ($max-$min);} Header (' content-type:image/png '); $im = Imagecreatetruecolor (at 255); $color 1 = imagecolorallocate ($im, 255, 255,) ; $color 2 = imagecolorallocate ($im, 0, 0, 0); for ($y =0; $y <512; $y + +) {for    ($x =0; $x <512; $x + +) {        $rand = randf Loat ();        if (Round ($rand, 2) >=0.5) {            imagesetpixel ($im, $x, $y, $color 1);        } else{            imagesetpixel ($im, $x, $y, $color 2);}}    Imagepng ($im); Imagedestroy ($im);? >

Random:

Random effects of Lcg_value ()

<?phpheader (' content-type:image/png '); $im = Imagecreatetruecolor (+), $color 1 = imagecolorallocate ($im, 255, 255, 255); $color 2 = imagecolorallocate ($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, $color 1);        } else{            imagesetpixel ($im, $x, $y, $color 2);}}    Imagepng ($im); Imagedestroy ($im);? >

Random:

comparing the random effect, it can be seen that the random effect generated by using Mt_rand () and Mt_getrandmax () algorithm is more chaotic than that of Lcg_value ().

This article explains the effect of PHP lcg_value and Mt_rand generated 0~1 random decimals, more relevant content please pay attention to the PHP Chinese web.

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