s_modf.c

标准c库代码,可以应用于各个系统提供了大量的基本函数

/* @(#)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.
 * ====================================================
 */

/*
FUNCTION
       <<modf>>, <<modff>>---split fractional and integer parts

INDEX
	modf
INDEX
	modff

ANSI_SYNOPSIS
	#include <math.h>
	double modf(double <[val]>, double *<[ipart]>);
        float modff(float <[val]>, float *<[ipart]>);

TRAD_SYNOPSIS
	#include <math.h>
	double modf(<[val]>, <[ipart]>)
        double <[val]>;
        double *<[ipart]>;

	float modff(<[val]>, <[ipart]>)
	float <[val]>;
        float *<[ipart]>;

DESCRIPTION
	<<modf>> splits the double <[val]> apart into an integer part
	and a fractional part, returning the fractional part and
	storing the integer part in <<*<[ipart]>>>.  No rounding
	whatsoever is done; the sum of the integer and fractional
	parts is guaranteed to be exactly  equal to <[val]>.   That
	is, if . <[realpart]> = modf(<[val]>, &<[intpart]>); then
	`<<<[realpart]>+<[intpart]>>>' is the same as <[val]>.
	<<modff>> is identical, save that it takes and returns
	<<float>> rather than <<double>> values. 

RETURNS
	The fractional part is returned.  Each result has the same
	sign as the supplied argument <[val]>.

PORTABILITY
	<<modf>> is ANSI C. <<modff>> is an extension.

QUICKREF
	modf  ansi pure 
	modff - pure

*/

/*
 * 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 "fdlibm.h"

#ifdef __STDC__
static const double one = 1.0;
#else
static double one = 1.0;
#endif

#ifdef __STDC__
	double modf(double x, double *iptr)
#else
	double modf(x, iptr)
	double x,*iptr;
#endif
{
#ifndef _DOUBLE_IS_32BITS
	__int32_t i0,i1,j0;
	__uint32_t i;
	EXTRACT_WORDS(i0,i1,x);
	j0 = ((i0>>20)&0x7ff)-0x3ff;	/* exponent of x */
	if(j0<20) {			/* integer part in high x */
	    if(j0<0) {			/* |x|<1 */
	        INSERT_WORDS(*iptr,i0&0x80000000,0);	/* *iptr = +-0 */
		return x;
	    } else {
		i = (0x000fffff)>>j0;
		if(((i0&i)|i1)==0) {		/* x is integral */
		    __uint32_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 (j0>51) {		/* no fraction part */
	    __uint32_t high;
	    *iptr = x*one;
	    GET_HIGH_WORD(high,x);
	    INSERT_WORDS(x,high&0x80000000,0);	/* return +-0 */
	    return x;
	} else {			/* fraction part in low x */
	    i = ((__uint32_t)(0xffffffff))>>(j0-20);
	    if((i1&i)==0) { 		/* x is integral */
	        __uint32_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;
	    }
	}
#else /* defined (_DOUBLE_IS_32BITS) */
	return (double) modff ((float) x, (float *) iptr);
#endif /* defined (_DOUBLE_IS_32BITS) */
}