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
     *
     * */