On Jan 19, 1:08 pm, Bill Woessner <woess...@nospicedham.gmail.com>
wrote:
> Success! Thanks to everyone who helped me out. This was a great
> little project to learn about inline assembly in GCC. For those of
> you who are interested, here's the final product:
>
> inline double DiffAngle(double theta1, double theta2)
> {
> double TWO_PI __attribute__ ((aligned (16)))(2 * M_PI),
> NEG_TWO_PI __attribute__ ((aligned (16)))(-TWO_PI);
> double delta(theta1 - theta2);
>
> asm("cmpnlesd %0, %1\n\t"
> "cmpltsd %0, %2\n\t"
> "andpd %3, %1\n\t"
> "andpd %4, %2\n\t"
> "addsd %1, %0\n\t"
> "addsd %2, %0\n\t"
> : "+x" (delta)
> : "x" (M_PI),
> "x" (-M_PI),
> "m" (TWO_PI),
> "m" (NEG_TWO_PI)
> :
> );
>
> return delta;
>
> }
>
> One final question - is it possible to declare TWO_PI and NEG_TWO_PI
> as const? And, if so, what constraint would I use? Right now, if I
> declare them const, I get the error "memory input 3 is not directly
> addressable".
>
> Thanks,
> Bill
This works for me:
#include <math.h>
double DiffAngle(double theta1, double theta2)
{
static const double TWO_PI __attribute__ ((aligned (16))) = 2 * M_PI;
double delta = theta1 - theta2;
asm("cmpnlesd %0, %1\n"
"cmpltsd %0, %2\n"
"andpd %3, %1\n"
"andpd %3, %2\n"
"addsd %1, %0\n"
"subsd %2, %0\n"
: "+x" (delta)
: "x" (M_PI), "x" (-M_PI), "m" (TWO_PI)
:
);
return delta;
}
(Using another trick, where the variable containing -2pi can be
replaced by a subtraction of +2pi.)
Steven
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