sysdeps/libm-ieee754/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 #if defined(LIBM_SCCS) && !defined(lint)
  17 static char rcsid[] = "$NetBSD: e_sqrtf.c,v 1.4 1995/05/10 20:46:19 jtc Exp $";
  18 #endif
  19
  20 #include "math.h"
  21 #include "math_private.h"
  22
  23 #ifdef __STDC__
  24 static  const float     one     = 1.0, tiny=1.0e-30;
  25 #else
  26 static  float   one     = 1.0, tiny=1.0e-30;
  27 #endif
  28
  29 #ifdef __STDC__
  30         float __ieee754_sqrtf(float x)
  31 #else
  32         float __ieee754_sqrtf(x)
  33         float x;
  34 #endif
  35 {
  36         float z;
  37         int32_t sign = (int)0x80000000;
  38         int32_t ix,s,q,m,t,i;
  39         u_int32_t r;
  40
  41         GET_FLOAT_WORD(ix,x);
  42
  43     /* take care of Inf and NaN */
  44         if((ix&0x7f800000)==0x7f800000) {
  45             return x*x+x;               /* sqrt(NaN)=NaN, sqrt(+inf)=+inf
  46                                            sqrt(-inf)=sNaN */
  47         }
  48     /* take care of zero */
  49         if(ix<=0) {
  50             if((ix&(~sign))==0) return x;/* sqrt(+-0) = +-0 */
  51             else if(ix<0)
  52                 return (x-x)/(x-x);             /* sqrt(-ve) = sNaN */
  53         }
  54     /* normalize x */
  55         m = (ix>>23);
  56         if(m==0) {                              /* subnormal x */
  57             for(i=0;(ix&0x00800000)==0;i++) ix<<=1;
  58             m -= i-1;
  59         }
  60         m -= 127;       /* unbias exponent */
  61         ix = (ix&0x007fffff)|0x00800000;
  62         if(m&1) /* odd m, double x to make it even */
  63             ix += ix;
  64         m >>= 1;        /* m = [m/2] */
  65
  66     /* generate sqrt(x) bit by bit */
  67         ix += ix;
  68         q = s = 0;              /* q = sqrt(x) */
  69         r = 0x01000000;         /* r = moving bit from right to left */
  70
  71         while(r!=0) {
  72             t = s+r;
  73             if(t<=ix) {
  74                 s    = t+r;
  75                 ix  -= t;
  76                 q   += r;
  77             }
  78             ix += ix;
  79             r>>=1;
  80         }
  81
  82     /* use floating add to find out rounding direction */
  83         if(ix!=0) {
  84             z = one-tiny; /* trigger inexact flag */
  85             if (z>=one) {
  86                 z = one+tiny;
  87                 if (z>one)
  88                     q += 2;
  89                 else
  90                     q += (q&1);
  91             }
  92         }
  93         ix = (q>>1)+0x3f000000;
  94         ix += (m <<23);
  95         SET_FLOAT_WORD(z,ix);
  96         return z;
  97 }