compiler/stdc/math/e_sqrtf.c

   1 /* e_sqrtf.c -- float version of e_sqrt.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
  16 #ifndef lint
  17 static char rcsid[] = "$FreeBSD: src/lib/msun/src/e_sqrtf.c,v 1.7 2002/05/28 18:15:04 alfred Exp $";
  18 #endif
  19
  20 #include "math.h"
  21 #include "math_private.h"
  22
  23 static  const float     one     = 1.0, tiny=1.0e-30;
  24
  25 float
  26 __ieee754_sqrtf(float x)
  27 {
  28         float z;
  29         int32_t sign = (int)0x80000000;
  30         int32_t ix,s,q,m,t,i;
  31         uint32_t r;
  32
  33         GET_FLOAT_WORD(ix,x);
  34
  35     /* take care of Inf and NaN */
  36         if((ix&0x7f800000)==0x7f800000) {
  37             return x*x+x;               /* sqrt(NaN)=NaN, sqrt(+inf)=+inf
  38                                            sqrt(-inf)=sNaN */
  39         }
  40     /* take care of zero */
  41         if(ix<=0) {
  42             if((ix&(~sign))==0) return x;/* sqrt(+-0) = +-0 */
  43             else if(ix<0)
  44                 return (x-x)/(x-x);             /* sqrt(-ve) = sNaN */
  45         }
  46     /* normalize x */
  47         m = (ix>>23);
  48         if(m==0) {                              /* subnormal x */
  49             for(i=0;(ix&0x00800000)==0;i++) ix<<=1;
  50             m -= i-1;
  51         }
  52         m -= 127;       /* unbias exponent */
  53         ix = (ix&0x007fffff)|0x00800000;
  54         if(m&1) /* odd m, double x to make it even */
  55             ix += ix;
  56         m >>= 1;        /* m = [m/2] */
  57
  58     /* generate sqrt(x) bit by bit */
  59         ix += ix;
  60         q = s = 0;              /* q = sqrt(x) */
  61         r = 0x01000000;         /* r = moving bit from right to left */
  62
  63         while(r!=0) {
  64             t = s+r;
  65             if(t<=ix) {
  66                 s    = t+r;
  67                 ix  -= t;
  68                 q   += r;
  69             }
  70             ix += ix;
  71             r>>=1;
  72         }
  73
  74     /* use floating add to find out rounding direction */
  75         if(ix!=0) {
  76             z = one-tiny; /* trigger inexact flag */
  77             if (z>=one) {
  78                 z = one+tiny;
  79                 if (z>one)
  80                     q += 2;
  81                 else
  82                     q += (q&1);
  83             }
  84         }
  85         ix = (q>>1)+0x3f000000;
  86         ix += (m <<23);
  87         SET_FLOAT_WORD(z,ix);
  88         return z;
  89 }