verify this http://www.laruence.com/2013/03/26/2884.html/comment-page-2#comment-31281

float-754-check.c

#include

int main() {

double a = 0.58, *aptr = &a;
float af = 0.58, *afptr = ⁡

printf(“%lu,%lx\n”,sizeof(a), *(long int *)aptr);
printf(“%lu,%x\n”,sizeof(af), *(int *)afptr);

// printf(“%lu,%d”,sizeof(a),(int) (a * 100) );

// int b = 21;
// printf(“%lu, %p\n”, sizeof(b), b);
// printf(“%lu, %d\n”, sizeof(b), (int)(float) b);
return 0;
}

good tools

https://babbage.cs.qc.cuny.edu/IEEE-754.old/Decimal.html

http://tool.oschina.net/hexconvert

good articles:
https://www.zhihu.com/question/21711083
https://zh.wikipedia.org/wiki/IEEE_754

> (= 1.000000001 1.000000002)
#f
> (= 1.0000000000001 1.0000000000002)
#f
> (= 1.000000000000001 1.000000000000002)
#f
> (= 1.0000000000000001 1.0000000000000002)
#f
> (= 1.00000000000000001 1.00000000000000002)
#t
> (= 10000000000000000.1 10000000000000000.2)
#t

<?php
$b = 1.0001;
$c = 1.0002;
var_dump($b == $c); // Y:F B:T X:T -------> false


$b = 1.000000001;
$c = 1.000000002;
var_dump($b == $c);  //Y:F B:F X:F -------> false

$b = 1.00000000000000001;
$c = 1.00000000000000002;
var_dump($b == $c); //Y:T B:T X:T -------> true


$b = 1.0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000001;
$c = 1.0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000002;
var_dump($b == $c); //Y:T B:T X:~ -------> true

from abaove zhihu link

例

问题：

• 浮点数能表示的最大数，（非正无穷） 是个整数，还是个浮点数
• printf 的输出

    float c = (1 << 24);  // 16777216.000000
    float b = c - 1, d = c + 1, e = d + 1, f = e + 1; // 16777215.000000 16777216.000000 16777216.000000 16777216.000000 16777216.000000
    printf("%f %f %f %f %f\n",b, c, d, e, f);

    //float b = c - 1, d = c + 1, e = c + 2, f = c + 3;//16777215.000000 16777216.000000 16777216.000000 16777218.000000 16777220.000000
    //printf("%f %f %f %f %f\n",b, c, d, e, f);

http://www.laruence.com/2011/12/19/2399.html

https://stackoverflow.com/questions/6936062/why-is-my-number-value-changing-using-number-format/6936191#6936191
http://news.php.net/php.general/326607

https://0.30000000000000004.com/

https://blog.csdn.net/Mr_eee/article/details/11768013

100.000100000000000332 == 100.000100000000000333 // true