C程序不能正确添加浮点数 [英] C program not adding float correctly

问题描述

  float * mutate（float * organism）{
 int一世; 
浮点数= 1; 
 static float newOrg [INPUTS] = {0}; 
 
（i = 0; i  if（rand（）％2 == 0）{
 sign = 1; 
} else {
 sign = -1; 
} 
 float temp =（organism [i] + sign）; 
 printf（bf：％f af：％f diff：％f sign：％f sign2：％f temp：％f\\\
\\\
，
 organism [i]，（organism （有机体[i] +符号） - 有机体[i]，
符号，符号+符号，温度）; 
 newOrg [i] =有机体[i] +符号; 
} 
 
 return newOrg; 
 
  

当 sign 是不是0，前两个％f s是相同的，第三个是0，也把总和放在一个变量中并没有帮助。这让我感到困惑！

输出：

  bf ：117810016.000000 af：117810016.000000 diff：0.000000 sign：1.000000 sign2：2.000000 temp：117810016.000000 
  

解决方案 有限精度 float 。
$ b

一个典型的 code>只能表示大约2 <32>个不同的数字。 117,810,016.0和1.0是其中两个。 117,810,017.0不是。因此， 117810016.0 + 1.0 的C总和得到了 117810016.0 的最佳答案。
$ b

使用像 double 这样的更高精度的类型往往会扩展+1精确数学的范围，但即使这样也不够精确（通常约为9.0 * 10e 15或2 53）。



如果代码要保留使用 float ，建议限制有机体[i] 为包含范围的值或±8,388,608.0（2 23



也许可以使用整数类型来完成这个任务，比如 long long 。

I have a method that looks like this:

float * mutate(float* organism){   
    int i;
    float sign = 1;
    static float newOrg[INPUTS] = {0};

    for (i = 0;i<INPUTS;i++){
        if (rand() % 2 == 0) {
            sign = 1;
        } else {
            sign = -1;
        }
        float temp = (organism[i] + sign);
        printf("bf: %f af: %f diff: %f sign: %f sign2: %f temp: %f\n\n",
            organism[i], (organism[i] + sign), (organism[i] + sign)-organism[i],
            sign, sign+sign, temp);
        newOrg[i] = organism[i] + sign;
    }

    return newOrg;
}

When sign is not 0 the first two "%f"s are the same and the 3rd is 0, also putting the sum in a variable didn't help. This is baffling me! I can post full code if needed.

Output:

bf: 117810016.000000 af: 117810016.000000 diff: 0.000000 sign: 1.000000 sign2: 2.000000 temp: 117810016.000000

解决方案

Finite precision of float.

A typical float can only represent about 2³² different numbers. 117,810,016.0 and 1.0 are two of them. 117,810,017.0 is not. So the C sum of 117810016.0 + 1.0 results in the "best" answer of 117810016.0.

Using a higher precision type like double often will extend the range of +1 exact math, but even that will not be exact with large enough values (typically about 9.0*10e¹⁵ or 2⁵³).

If code is to retain using float, suggest limiting organism[i] to values to the inclusive range or ±8,388,608.0 (2²³).

Perhaps can code simply use integer types for this task like long long.

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