>
>If you know that the exponent is integral you may want to have a look at
>GCC's __builtin_powi* functions.
>
>http://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html
>
>You asked for a base of 2, maybe ldexp() fits your use case.
>
>Handling integral exponents separately will increase the code size
>because the exponent must be checked at run time and extra code must be
>executed in that case.
Tried an experiment with the the program that follow in studio to calculate the
differences.
int getVal () {
return 3;
}
int main(void)
{
double d = __builtin_powi (7, getVal ());
double f = pow (7, getVal ());
while(1)
{
printf ("%f", d);
printf ("%f", d);
}
}
The builtin which called __powisf2 in libgcc.
The code size and cycles obtained in avrstudio6 were as follows.
Function Size Cycles
pow 152 5525
__powisf2 210 452
Also the code in libc seems to have checks already to check if its integer so
would calling the libgcc function be advisable ?
-George-
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