lib/libm/src/s_modf.c
/* @(#)s_modf.c 5.1 93/09/24 */
/*
 * ====================================================
 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
 *
 * Developed at SunPro, a Sun Microsystems, Inc. business.
 * Permission to use, copy, modify, and distribute this
 * software is freely granted, provided that this notice
 * is preserved.
 * ====================================================
 */

#include <sys/cdefs.h>
#if defined(LIBM_SCCS) && !defined(lint)
__RCSID("$NetBSD: s_modf.c,v 1.14 2010/01/27 14:07:41 drochner Exp $");
#endif

/*
 * modf(double x, double *iptr)
 * return fraction part of x, and return x's integral part in *iptr.
 * Method:
 *	Bit twiddling.
 *
 * Exception:
 *	No exception.
 */

#include "math.h"
#include "math_private.h"

static const double one = 1.0;

double
modf(double x, double *iptr)
{
	int32_t i0,i1,jj0;
	u_int32_t i;
	EXTRACT_WORDS(i0,i1,x);
	jj0 = (((uint32_t)i0>>20)&0x7ff)-0x3ff;	/* exponent of x */
	if(jj0<20) {			/* integer part in high x */
	    if(jj0<0) {			/* |x|<1 */
	        INSERT_WORDS(*iptr,i0&0x80000000,0);	/* *iptr = +-0 */
		return x;
	    } else {
		i = (0x000fffff)>>jj0;
		if(((i0&i)|i1)==0) {		/* x is integral */
		    u_int32_t high;
		    *iptr = x;
		    GET_HIGH_WORD(high,x);
		    INSERT_WORDS(x,high&0x80000000,0);	/* return +-0 */
		    return x;
		} else {
		    INSERT_WORDS(*iptr,i0&(~i),0);
		    return x - *iptr;
		}
	    }
	} else if (jj0>51) {		/* no fraction part */
	    u_int32_t high;
	    *iptr = x*one;
	    if (jj0 == 0x400)		/* +-inf or NaN */
		return 0.0 / x;		/* +-0 or NaN */
	    GET_HIGH_WORD(high,x);
	    INSERT_WORDS(x,high&0x80000000,0);	/* return +-0 */
	    return x;
	} else {			/* fraction part in low x */
	    i = ((u_int32_t)(0xffffffff))>>(jj0-20);
	    if((i1&i)==0) { 		/* x is integral */
	        u_int32_t high;
		*iptr = x;
		GET_HIGH_WORD(high,x);
		INSERT_WORDS(x,high&0x80000000,0);	/* return +-0 */
		return x;
	    } else {
	        INSERT_WORDS(*iptr,i0,i1&(~i));
		return x - *iptr;
	    }
	}
}
