Routine to convert between IEEE and VAX floating point ?

[Walter Bright]

>From article <1023 at rna.UUCP>, by dan at rna.UUCP (Dan Ts'o):
< 	Does anyone have a C routine to convert from IEEE floating point
< to VAX D format floating point ?

Here's one I wrote to convert from VAX to PC 64-bit doubles. You could
easily reverse it to go the other way.

main()
{
	double d1,d2;
	long *p;

	while (1)
	{	scanf(" %lf",&d1);
		p = (long *) &d1;
		printf("x%08lx,x%08lx\n",p[1],p[0]);
		vaxdbl_to_pcdbl(&d1,&d2);
		p = (long *) &d2;
		printf("x%08lx,x%08lx\n",p[1],p[0]);
	}
}

vaxdbl_to_pcdbl(pvax,ppc)
unsigned long *pvax,*ppc;
{
	unsigned sign,exponent;
	unsigned long fraction;

	sign = (*pvax & 0x8000) != 0;
	exponent = (*pvax >> 7) & 0xFF;
	fraction = ((*pvax & 0x7F) << 16) | (*pvax >> 16);
	printf("sign = %d, exponent = x%x, fraction = x%lx\n",
		sign,exponent,fraction);
	if (sign == 0 && exponent == 0)
	{	ppc[0] = 0;
		ppc[1] = 0;
		return;
	}
	/* Put sign in result	*/
	ppc[1] = (unsigned long) sign << 31;
	/* Compute new exponent	*/
	exponent += 0x3FF - 0x80 - 1;
	ppc[1] |= (unsigned long) exponent << 20;
	/* OR in fraction	*/
	ppc[1] |= (fraction >> 3);
	ppc[0] = (fraction << 29) | (pvax[1] >> 3);
}