---
title: atan2pi
description: "计算y/x的反正切值，并将结果再除以π。"
url: https://www.hikunpeng.com/document/detail/zh/hpchistory/hpckit/develop2400/kunpengaccel_kml_0165.html
sourcePath: /source/zh/hpchistory/hpckit/develop2400/kunpengaccel_kml_0165.html
indexId: ad81f1a28c508cb75a87acd130e20430f77e799f47cbd0826f602017ac4f29c467
---
# atan2pi

计算y/x的反正切值，并将结果再除以π。

#### 接口定义

C interface：

float atan2pif(float y, float x);

double atan2pi(double y, double x);


#### 参数

| 参数名 | 类型 | 描述 | 输入/输出 |
| --- | --- | --- | --- |
| x | 在atan2df中，x是单精度浮点类型。 在atan2d中，x是双精度浮点类型。 | 表示输入数据的浮点值。 | 输入 |
| y | 在atan2df中，y是单精度浮点类型。 在atan2d中，y是双精度浮点类型。 | 表示输入数据的浮点值。 | 输入 |


#### 返回值

- 正常区间：计算y/x的反正切值，并将结果再除以π，即result = atan(y/x) / π，res∈[-1, +1]。
- 特殊区间：如下所示。| 输入值（y） | 输入值（x） | 输出值（result） |
| --- | --- | --- |
| +0 | +0 | +0 |
| +0 | \-0 | +1 |
| +0 | inf | +0 |
| +0 | \-inf | +1 |
| +0 | nan | nan |
| \-0 | +0 | \-0 |
| \-0 | \-0 | \-1 |
| \-0 | inf | \-0 |
| \-0 | \-inf | \-1 |
| \-0 | nan | nan |
| inf | +0 | 0.5 |
| inf | \-0 | 0.5 |
| inf | inf | 0.25 |
| inf | \-inf | 0.75 |
| inf | nan | nan |
| \-inf | +0 | \-0.5 |
| \-inf | \-0 | \-0.5 |
| \-inf | inf | \-0.25 |
| \-inf | \-inf | \-0.75 |
| \-inf | nan | nan |
| nan | +0 | nan |
| nan | \-0 | nan |
| nan | inf | nan |
| nan | \-inf | nan |
| nan | nan | nan |


#### 依赖

C: "km.h"


#### 示例

C interface：```
// typical usage
    float x1 = -1.0, x2 = 1.0, x3 = 0.5, x4 = -0.5;
    // special handling
    float a = 0.0, b = INFINITY, c = -INFINITY, d = NAN;
    // print result
    printf("atan2pi(1.0, 1.0) = %.15f\n", atan2pi(x1, x1));
    printf("atan2pi(-1.0, -1.0) = %.15f\n", atan2pi(x2, x2));
    printf("atan2pi(0.5, 0.5) = %.15f\n", atan2pi(x3, x3));
    printf("atan2pi(-0.5, -0.5) = %.15f\n", atan2pi(x4, x4));
    printf("atan2pi(0.0, 0.0) = %.15f\n", atan2pi(a, a));
    printf("atan2pi(-0.0, -0.0) = %.15f\n", atan2pi(-a, -a));
    printf("atan2pi(INFINITY, INFINITY) = %.15f\n", atan2pi(b, b));
    printf("atan2pi(-INFINITY, -INFINITY) = %.15f\n", atan2pi(c, c));
    printf("atan2pi(NAN, NAN) = %.15f\n", atan2pi(d, d));
    /*
     *  atan2pi(1.0, 1.0) = -0.750000000000000
     *  atan2pi(-1.0, -1.0) = 0.250000000000000
     *  atan2pi(0.5, 0.5) = 0.250000000000000
     *  atan2pi(-0.5, -0.5) = -0.750000000000000
     *  atan2pi(0.0, 0.0) = 0.000000000000000
     *  atan2pi(-0.0, -0.0) = -1.000000000000000
     *  atan2pi(INFINITY, INFINITY) = 0.250000000000000
     *  atan2pi(-INFINITY, -INFINITY) = -0.750000000000000
     *  atan2pi(NAN, NAN) = nan
     *
     * */
```