Output bit string of double value.

dblval.c

#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <math.h>

typedef union U_DBL_INT {
	double d;
	uint64_t i;
} dbl_int_t;

static const char *
u64_to_bitstr(uint64_t x)
{
	static char buf[65];
	int32_t k;

	buf[64] = 0;
	for (k=0; k<64; k+=1) {
		char c = '0';
		if ((x & 1) == 1) {
			c = '1';
		}
		else {
			c = '0';
		}
		buf[63-k] = c;
		x = x >> 1;
	}

	return buf;
}

int
main(int argc, char * argv[])
{
	double x;
	double y;
	dbl_int_t v;

	x = 1.0/1024.0;
	y = 1.0 - x*x*x*x*x*0.25;
	v.d = cbrt(y);

	printf("%s\n", u64_to_bitstr(v.i));
	printf("%.16e\n", v.d);

	return 0;
}