---
title: acospi
description: "计算输入实数的反余弦值除以π。"
url: https://www.hikunpeng.com/document/detail/zh/kunpengboostkithistory/2300/accel/kunpengaccel_kml_16_0363.html
sourcePath: /source/zh/kunpengboostkithistory/2300/accel/kunpengaccel_kml_16_0363.html
indexId: bda280db625666a14deae7abb3d676a12ef1c267f26ae41a9571a3e02d6e57fe74
---
# acospi

计算输入实数的反余弦值除以π。

#### 接口定义

C interface：

float acospif(float x);

double acospi(double x);


#### 参数

| 参数名 | 类型 | 描述 | 输入/输出 |
| --- | --- | --- | --- |
| x | 在acospif中，x是单精度浮点类型。 在acospi中，x是双精度浮点类型。 | 表示余弦值的浮点值。 | 输入 |


#### 返回值

- 返回输入实数x的反余弦函数值除以π的值y=acos(x) / π，y ∈ [0, 1]。
- 输入±0，返回0.5。
- 输入x为1，返回+0。
- 输入x为-1，返回1。
- 输入|x|>1，返回nan。
- 输入±∞，返回nan。
- 输入±nan，返回±nan。


#### 依赖

C: "km.h"


#### 示例

C interface：

```
// print result
printf("acospi(0.0) = %.15f\n", acospi(0.0));
printf("acospi(-0.0) = %.15f\n", acospi(-0.0));
printf("acospi(0.25) = %.15f\n", acospi(0.25));
printf("acospi(-0.25) = %.15f\n", acospi(-0.25));
printf("acospi(0.5) = %.15f\n", acospi(0.5));
printf("acospi(-0.5) = %.15f\n", acospi(-0.5));
printf("acospi(1.0) = %.15f\n", acospi(1.0));
printf("acospi(-1.0) = %.15f\n", acospi(-1.0));
printf("acospi(INFINITY) = %.15f\n", acospi(INFINITY));
printf("acospi(-INFINITY) = %.15f\n", acospi(-INFINITY));
printf("acospi(NAN) = %.15f\n", acospi(NAN));
printf("acospi(-NAN) = %.15f\n", acospi(-NAN));
/*
* acospi(0.0) = 0.500000000000000
* acospi(-0.0) = 0.500000000000000
* acospi(0.25) = 0.419569376744834
* acospi(-0.25) = 0.580430623255166
* acospi(0.5) = 0.333333333333333
* acospi(-0.5) = 0.666666666666667
* acospi(1.0) = 0.000000000000000
* acospi(-1.0) = 1.000000000000000
* acospi(INFINITY) = nan
* acospi(-INFINITY) = nan
* acospi(NAN) = nan
* acospi(-NAN) = -nan
*
* */
```