newthread_fpu.c

#include <math.h>
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

static double
read_xmm15(void)
{
	double x;

	asm volatile("movsd\t%%xmm15,%0" : "=x" (x));
	return (x);
}

static void
write_xmm15(const double x)
{
	asm volatile("movsd\t%0,%%xmm15" : : "x" (x) : "xmm15");
}

static void *
thrf(void *arg)
{
	double x;

	(void)arg;
	x = read_xmm15();
	printf("t %e\n", x);
	return (NULL);
}

int
main(void)
{
	pthread_t thr;
	int error;

	printf("m %e\n", M_PI);
	write_xmm15(M_PI);
	error = pthread_create(&thr, NULL, thrf, NULL);
	if (error != 0) {
		fprintf(stderr, "pthread_create %s\n", strerror(error));
		exit(1);
	}

	error = pthread_join(thr, NULL);
	if (error != 0) {
		fprintf(stderr, "pthread_join %s\n", strerror(error));
		exit(1);
	}
}