scalb
计算x * 2^y的值。
接口定义
C interface：
float scalbf(float x, float y);
double scalb(double x, double y);
long double scalb(long double x, long double y);
参数
参数名 |
类型 |
描述 |
输入/输出 |
|---|---|---|---|
x |
|
表示输入数据的浮点值。 |
输入 |
y |
|
表示输入数据的浮点值。 |
输入 |
返回值
- 输入x为nan，输入y为任意值，返回x*y。
- 输入y为nan或+∞，输入x为任意值，返回x*y。
- 输入x为±0，y为-∞，返回x。
- 输入y为-∞，x非0，返回±0（符号与x相同）。
- 输入y为非整数，输入x为任意值，返回nan。
依赖
C: "km.h"
示例
C interface：
// typical usage
double x1 = 0.0, x2 = -0.0, x3 = 2.0, x4 = 1100.0;
double y1 = -0.0, y2 = 0.0, y3 = 3.0, y4 = 2.1;
// special handing
double a = INFINITY, b = -INFINITY, c = NAN;
printf("scalb(0.0, -0.0) = %.15f\n", scalb(x1, y1));
printf("scalb(-0.0, 0.0) = %.15f\n", scalb(x2, y2));
printf("scalb(2.0, 3.0) = %.15f\n", scalb(x3, y3));
printf("scalb(2.0, 2.1) = %.15f\n", scalb(x3, y4));
printf("scalb(0.0, -INFINITY) = %.15f\n", scalb(x1, b));
printf("scalb(-0.0, -INFINITY) = %.15f\n", scalb(y1, b));
printf("scalb(2.0, -INFINITY) = %.15f\n", scalb(x3, b));
printf("scalb(2.0, 1100.0) = %.15f\n", scalb(x3, x4));
printf("scalb(INFINITY, 2.0) = %.15f\n", scalb(a, x2));
printf("scalb(-INFINITY, 2.0) = %.15f\n", scalb(b, x2));
printf("scalb(NAN, 2.0) = %.15f\n", scalb(c, x3));
printf("scalb(NAN, INFINITY) = %.15f\n", scalb(c, a));
printf("scalb(NAN, -INFINITY) = %.15f\n", scalb(c, b));
printf("scalb(INFINITY, -INFINITY) = %.15f\n", scalb(a, b));
/*
* scalb(0.0, -0.0) = 0.000000000000000
* scalb(-0.0, 0.0) = -0.000000000000000
* scalb(2.0, 3.0) = 16.000000000000000
* scalb(2.0, 2.1) = nan
* scalb(0.0, -INFINITY) = 0.000000000000000
* scalb(-0.0, -INFINITY) = -0.000000000000000
* scalb(2.0, -INFINITY) = 0.000000000000000
* scalb(2.0, 1100.0) = inf
* scalb(INFINITY, 2.0) = inf
* scalb(-INFINITY, 2.0) = -inf
* scalb(NAN, 2.0) = nan
* scalb(NAN, INFINITY) = nan
* scalb(NAN, -INFINITY) = nan
* scalb(INFINITY, -INFINITY) = nan
*
* */
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