sf_nextafter.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

/* sf_nextafter.c -- float version of s_nextafter.c.
 * Conversion to float by Ian Lance Taylor, Cygnus Support, [e-mail].
 */

/*
 * ====================================================
 * 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 "fdlibm.h"

#ifdef __STDC__
	float nextafterf(float x, float y)
#else
	float nextafterf(x,y)
	float x,y;
#endif
{
	__int32_t	hx,hy,ix,iy;

	GET_FLOAT_WORD(hx,x);
	GET_FLOAT_WORD(hy,y);
	ix = hx&0x7fffffff;		/* |x| */
	iy = hy&0x7fffffff;		/* |y| */

	if((ix>0x7f800000) ||   /* x is nan */ 
	   (iy>0x7f800000))     /* y is nan */ 
	   return x+y;				
	if(x==y) return x;		/* x=y, return x */
	if(ix==0) {				/* x == 0 */
	    SET_FLOAT_WORD(x,(hy&0x80000000)|1);/* return +-minsubnormal */
	    y = x*x;
	    if(y==x) return y; else return x;	/* raise underflow flag */
	} 
	if(hx>=0) {				/* x > 0 */
	    if(hx>hy) {				/* x > y, x -= ulp */
		hx -= 1;
	    } else {				/* x < y, x += ulp */
		hx += 1;
	    }
	} else {				/* x < 0 */
	    if(hy>=0||hx>hy){			/* x < y, x -= ulp */
		hx -= 1;
	    } else {				/* x > y, x += ulp */
		hx += 1;
	    }
	}
	hy = hx&0x7f800000;
	if(hy>=0x7f800000) return x+x;	/* overflow  */
	if(hy<0x00800000) {		/* underflow */
	    y = x*x;
	    if(y!=x) {		/* raise underflow flag */
	        SET_FLOAT_WORD(y,hx);
		return y;
	    }
	}
	SET_FLOAT_WORD(x,hx);
	return x;
}