---
title: cospi
description: "计算输入实数与π相乘的余弦值。"
url: https://www.hikunpeng.com/document/detail/zh/hpchistory/hpckit/develop2400/kunpengaccel_kml_0151.html
sourcePath: /source/zh/hpchistory/hpckit/develop2400/kunpengaccel_kml_0151.html
indexId: b5a8381343109d7b1fcca199fd7565da878e612428ddbce37cf21293b44cd8f767
---
# cospi

计算输入实数与π相乘的余弦值。

#### 接口定义

C interface：

float cospif(float x);

double cospi(double x);


#### 参数

| 参数名 | 类型 | 描述 | 输入/输出 |
| --- | --- | --- | --- |
| x | 在cospif中，x是单精度浮点类型。 在cospi中，x是双精度浮点类型。 | 表示输入数据的浮点值。 | 输入 |


#### 返回值

- 返回x乘以π的余弦函数值y=cos(x * π)，y ∈ [-1, +1]。
- 输入+0，返回1。
- 输入-0，返回1。
- 输入±∞，返回nan。
- 输入nan，返回nan。


#### 依赖

C: "km.h"


#### 示例

C interface：```
// print result
    printf("cospi(0.0) = %.15f\n", cospi(0.0));
    printf("cospi(-0.0) = %.15f\n", cospi(-0.0));
    printf("cospi(0.25) = %.15f\n", cospi(0.25));
    printf("cospi(-0.25) = %.15f\n", cospi(-0.25));
    printf("cospi(0.5) = %.15f\n", cospi(0.5));
    printf("cospi(-0.5) = %.15f\n", cospi(-0.5));
    printf("cospi(1.0) = %.15f\n", cospi(1.0));
    printf("cospi(-1.0) = %.15f\n", cospi(-1.0));
    printf("cospi(2.0) = %.15f\n", cospi(2.0));
    printf("cospi(-2.0) = %.15f\n", cospi(-2.0));
    printf("cospi(INFINITY) = %.15f\n", cospi(INFINITY));
    printf("cospi(-INFINITY) = %.15f\n", cospi(-INFINITY));
    printf("cospi(NAN) = %.15f\n", cospi(NAN));
    printf("cospi(-NAN) = %.15f\n", cospi(-NAN));
    /* 
     * cospi(0.0) = 1.000000000000000
     * cospi(-0.0) = 1.000000000000000
     * cospi(0.25) = 0.707106781186548
     * cospi(-0.25) = 0.707106781186548
     * cospi(0.5) = 0.000000000000000
     * cospi(-0.5) = 0.000000000000000
     * cospi(1.0) = -1.000000000000000
     * cospi(-1.0) = -1.000000000000000
     * cospi(2.0) = 1.000000000000000
     * cospi(-2.0) = 1.000000000000000
     * cospi(INFINITY) = nan
     * cospi(-INFINITY) = nan
     * cospi(NAN) = nan
     * cospi(-NAN) = -nan
     * 
     * */
```