lib/libm/src/s_rintf.c

   1 /* s_rintf.c -- float version of s_rint.c.
   2  * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
   3  */
   4
   5 /*
   6  * ====================================================
   7  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
   8  *
   9  * Developed at SunPro, a Sun Microsystems, Inc. business.
  10  * Permission to use, copy, modify, and distribute this
  11  * software is freely granted, provided that this notice
  12  * is preserved.
  13  * ====================================================
  14  *
  15  * $NetBSD: s_rintf.c,v 1.8 2006/08/01 20:14:35 drochner Exp $
  16  * $DragonFly: src/lib/libm/src/s_rintf.c,v 1.2 2007/06/17 02:27:53 pavalos Exp $
  17  */
  18
  19 #include <math.h>
  20 #include "math_private.h"
  21
  22 static const float
  23 TWO23[2]={
  24   8.3886080000e+06, /* 0x4b000000 */
  25  -8.3886080000e+06, /* 0xcb000000 */
  26 };
  27
  28 float
  29 rintf(float x)
  30 {
  31         int32_t i0,j0,sx;
  32         u_int32_t i,i1;
  33 #ifdef __i386__ /* XXX gcc4 will omit the rounding otherwise */
  34         volatile
  35 #endif
  36                 float w;
  37         float t;
  38         GET_FLOAT_WORD(i0,x);
  39         sx = (i0>>31)&1;
  40         j0 = ((i0>>23)&0xff)-0x7f;
  41         if(j0<23) {
  42             if(j0<0) {
  43                 if((i0&0x7fffffff)==0) return x;
  44                 i1 = (i0&0x07fffff);
  45                 i0 &= 0xfff00000;
  46                 i0 |= ((i1|-i1)>>9)&0x400000;
  47                 SET_FLOAT_WORD(x,i0);
  48                 w = TWO23[sx]+x;
  49                 t =  w-TWO23[sx];
  50                 GET_FLOAT_WORD(i0,t);
  51                 SET_FLOAT_WORD(t,(i0&0x7fffffff)|(sx<<31));
  52                 return t;
  53             } else {
  54                 i = (0x007fffff)>>j0;
  55                 if((i0&i)==0) return x; /* x is integral */
  56                 i>>=1;
  57                 if((i0&i)!=0) i0 = (i0&(~i))|((0x100000)>>j0);
  58             }
  59         } else {
  60             if(j0==0x80) return x+x;    /* inf or NaN */
  61             else return x;              /* x is integral */
  62         }
  63         SET_FLOAT_WORD(x,i0);
  64         w = TWO23[sx]+x;
  65         return w-TWO23[sx];
  66 }