blob: 54e538896ee556c4a5eaa14c3791a5a72f71d073 (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
|
#include <math.h>
#include <stdio.h>
double gsl_pow_uint(double x, unsigned int n);
double gsl_pow_int(double x, int n)
{
unsigned int un;
if(n < 0) {
x = 1.0/x;
un = -n;
} else {
un = n;
}
return gsl_pow_uint(x, un);
}
double gsl_pow_uint(double x, unsigned int n)
{
double value = 1.0;
/* repeated squaring method
* returns 0.0^0 = 1.0, so continuous in x
*/
do {
if(n & 1) value *= x; /* for n odd */
n >>= 1;
x *= x;
} while (n);
return value;
}
int main() {
double y, y_expected;
for (int n = -9; n < 10; n++) {
y = gsl_pow_int (-3.14, n);
y_expected = pow (-3.14, n);
printf("%d %g %g\n", n, y, y_expected);
}
return 0;
}
|