js/src/fdlibm/s_nextafter.c

   1 /* -*- Mode: C; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
   2  *
   3  * ***** BEGIN LICENSE BLOCK *****
   4  * Version: MPL 1.1/GPL 2.0/LGPL 2.1
   5  *
   6  * The contents of this file are subject to the Mozilla Public License Version
   7  * 1.1 (the "License"); you may not use this file except in compliance with
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   9  * http://www.mozilla.org/MPL/
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  12  * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
  13  * for the specific language governing rights and limitations under the
  14  * License.
  15  *
  16  * The Original Code is Mozilla Communicator client code, released
  17  * March 31, 1998.
  18  *
  19  * The Initial Developer of the Original Code is
  20  * Sun Microsystems, Inc.
  21  * Portions created by the Initial Developer are Copyright (C) 1998
  22  * the Initial Developer. All Rights Reserved.
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  26  * Alternatively, the contents of this file may be used under the terms of
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  38  * ***** END LICENSE BLOCK ***** */
  39
  40 /* @(#)s_nextafter.c 1.3 95/01/18 */
  41 /*
  42  * ====================================================
  43  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
  44  *
  45  * Developed at SunSoft, a Sun Microsystems, Inc. business.
  46  * Permission to use, copy, modify, and distribute this
  47  * software is freely granted, provided that this notice
  48  * is preserved.
  49  * ====================================================
  50  */
  51
  52 /* IEEE functions
  53  *      nextafter(x,y)
  54  *      return the next machine floating-point number of x in the
  55  *      direction toward y.
  56  *   Special cases:
  57  */
  58
  59 #include "fdlibm.h"
  60
  61 #ifdef __STDC__
  62         double fd_nextafter(double x, double y)
  63 #else
  64         double fd_nextafter(x,y)
  65         double x,y;
  66 #endif
  67 {
  68         int     hx,hy,ix,iy;
  69         unsigned lx,ly;
  70         fd_twoints ux, uy;
  71
  72         ux.d = x; uy.d = y;
  73         hx = __HI(ux);          /* high word of x */
  74         lx = __LO(ux);          /* low  word of x */
  75         hy = __HI(uy);          /* high word of y */
  76         ly = __LO(uy);          /* low  word of y */
  77         ix = hx&0x7fffffff;             /* |x| */
  78         iy = hy&0x7fffffff;             /* |y| */
  79
  80         if(((ix>=0x7ff00000)&&((ix-0x7ff00000)|lx)!=0) ||   /* x is nan */
  81            ((iy>=0x7ff00000)&&((iy-0x7ff00000)|ly)!=0))     /* y is nan */
  82            return x+y;
  83         if(x==y) return x;              /* x=y, return x */
  84         if((ix|lx)==0) {                        /* x == 0 */
  85             ux.d = x;
  86             __HI(ux) = hy&0x80000000;   /* return +-minsubnormal */
  87             __LO(ux) = 1;
  88             x = ux.d;
  89             y = x*x;
  90             if(y==x) return y; else return x;   /* raise underflow flag */
  91         }
  92         if(hx>=0) {                             /* x > 0 */
  93             if(hx>hy||((hx==hy)&&(lx>ly))) {    /* x > y, x -= ulp */
  94                 if(lx==0) hx -= 1;
  95                 lx -= 1;
  96             } else {                            /* x < y, x += ulp */
  97                 lx += 1;
  98                 if(lx==0) hx += 1;
  99             }
 100         } else {                                /* x < 0 */
 101             if(hy>=0||hx>hy||((hx==hy)&&(lx>ly))){/* x < y, x -= ulp */
 102                 if(lx==0) hx -= 1;
 103                 lx -= 1;
 104             } else {                            /* x > y, x += ulp */
 105                 lx += 1;
 106                 if(lx==0) hx += 1;
 107             }
 108         }
 109         hy = hx&0x7ff00000;
 110         if(hy>=0x7ff00000) return x+x;  /* overflow  */
 111         if(hy<0x00100000) {             /* underflow */
 112             y = x*x;
 113             if(y!=x) {          /* raise underflow flag */
 114                 uy.d = y;
 115                 __HI(uy) = hx; __LO(uy) = lx;
 116                 y = uy.d;
 117                 return y;
 118             }
 119         }
 120         ux.d = x;
 121         __HI(ux) = hx; __LO(ux) = lx;
 122         x = ux.d;
 123         return x;
 124 }