---
title: cacos
description: "计算复数反余弦值。"
url: https://www.hikunpeng.com/document/detail/zh/kunpengboostkithistory/240RC2/accel/kunpengaccel_kml_16_0585.html
sourcePath: /source/zh/kunpengboostkithistory/240RC2/accel/kunpengaccel_kml_16_0585.html
indexId: afc76ad734de43dfff0cda6ba5f1a4fe31a7a2a3c0c4d629c1d62cf7085403b076
---
# cacos

计算复数反余弦值。

#### 接口定义

C interface：

float complex cacosf(float complex x);

double complex cacos(double complex x);


#### 参数

| 参数名 | 类型 | 描述 | 输入/输出 |
| --- | --- | --- | --- |
| x | 在cacosf中，x是复数单精度浮点类型。 在cacos中，x是复数双精度浮点类型。 | 表示输入数据的浮点值。 | 输入 |


#### 返回值

- 正常区间：返回x复数的反余弦值。
- 特殊区间：如下所示。| 输入值实部（x.real） | 输入值虚部（x.imag） | 输出值实部（y.real） | 输出值虚部（y.imag） |
| --- | --- | --- | --- |
| 0 | 0 | pi/2 | 0 |
| 0 | 0 | pi/2 | 0 |
| 0 | inf | pi/2 | \-inf |
| 0 | \-inf | pi/2 | inf |
| 0 | snan | pi/2 | nan |
| 0 | \-snan | pi/2 | nan |
| 0 | qnan | pi/2 | nan |
| 0 | \-qnan | pi/2 | nan |
| 0 | 0 | pi/2 | 0 |
| 0 | 0 | pi/2 | 0 |
| 0 | inf | pi/2 | \-inf |
| 0 | \-inf | pi/2 | inf |
| 0 | snan | pi/2 | nan |
| 0 | \-snan | pi/2 | nan |
| 0 | qnan | pi/2 | nan |
| 0 | \-qnan | pi/2 | nan |
| inf | 0 | 0 | \-inf |
| inf | 0 | 0 | inf |
| inf | inf | pi/4 | \-inf |
| inf | \-inf | pi/4 | inf |
| inf | snan | nan | \-inf |
| inf | \-snan | nan | \-inf |
| inf | qnan | nan | \-inf |
| inf | \-qnan | nan | \-inf |
| \-inf | 0 | pi | \-inf |
| \-inf | 0 | pi | inf |
| \-inf | inf | 3\*pi/4 | \-inf |
| \-inf | \-inf | 3\*pi/4 | inf |
| \-inf | snan | nan | \-inf |
| \-inf | \-snan | nan | \-inf |
| \-inf | qnan | nan | \-inf |
| \-inf | \-qnan | nan | \-inf |
| snan | 0 | nan | nan |
| snan | 0 | nan | nan |
| snan | inf | nan | \-inf |
| snan | \-inf | nan | inf |
| snan | snan | nan | nan |
| snan | \-snan | nan | nan |
| snan | qnan | nan | nan |
| snan | \-qnan | nan | nan |
| \-snan | 0 | nan | nan |
| \-snan | 0 | nan | nan |
| \-snan | inf | nan | \-inf |
| \-snan | \-inf | nan | inf |
| \-snan | snan | nan | nan |
| \-snan | \-snan | nan | nan |
| \-snan | qnan | nan | nan |
| \-snan | \-qnan | nan | nan |
| qnan | 0 | nan | nan |
| qnan | 0 | nan | nan |
| qnan | inf | nan | \-inf |
| qnan | \-inf | nan | inf |
| qnan | snan | nan | nan |
| qnan | \-snan | nan | nan |
| qnan | qnan | nan | nan |
| qnan | \-qnan | nan | nan |
| \-qnan | 0 | nan | nan |
| \-qnan | 0 | nan | nan |
| \-qnan | inf | nan | \-inf |
| \-qnan | \-inf | nan | inf |
| \-qnan | snan | nan | nan |
| \-qnan | \-snan | nan | nan |
| \-qnan | qnan | nan | nan |
| \-qnan | \-qnan | nan | nan |


#### 依赖

C: "kc.h"


#### 示例

C interface：
```
// typical usage
double x1 = INFINITY, y1 = INFINITY;
double x2 = 2.0, y2 = 3.0;
double x3 = -2.5, y3 = -3.4;
double x4 = NAN, y4 = NAN;
double x5 = 0, y5 = 0;
// print result
printf("/*\n");
printf(" * cacos(%.2f + %.2f*I) = %.6f\n", x1, y1, cacos(__builtin_complex(x1, y1)));
printf(" * cacos(%.2f + %.2f*I) = %.6f\n", x2, y2, cacos(__builtin_complex(x2, y2)));
printf(" * cacos(%.2f + %.2f*I) = %.6f\n", x3, y3, cacos(__builtin_complex(x3, y3)));
printf(" * cacos(%.2f + %.2f*I) = %.6f\n", x4, y4, cacos(__builtin_complex(x4, y4)));
printf(" * cacos(%.2f + %.2f*I) = %.6f\n", x5, y5, cacos(__builtin_complex(x5, y5)));
printf(" **/\n");
/*
* cacos(inf + inf*I) = 0.785398
* cacos(2.00 + 3.00*I) = 1.000144
* cacos(-2.50 + -3.40*I) = 2.191594
* cacos(nan + nan*I) = nan
* cacos(0.00 + 0.00*I) = 1.570796
**/
```