toolchain/gcc/newlib/libm/math/ef_sqrt.c

   1 /* ef_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 #include "fdlibm.h"
  17
  18 #ifdef __STDC__
  19 static  const float     one     = 1.0, tiny=1.0e-30;
  20 #else
  21 static  float   one     = 1.0, tiny=1.0e-30;
  22 #endif
  23
  24 #ifdef __STDC__
  25         float __ieee754_sqrtf(float x)
  26 #else
  27         float __ieee754_sqrtf(x)
  28         float x;
  29 #endif
  30 {
  31         float z;
  32         __int32_t       sign = (__int32_t)0x80000000;
  33         __uint32_t r,hx;
  34         __int32_t ix,s,q,m,t,i;
  35
  36         GET_FLOAT_WORD(ix,x);
  37         hx = ix&0x7fffffff;
  38
  39     /* take care of Inf and NaN */
  40         if(!FLT_UWORD_IS_FINITE(hx))
  41             return x*x+x;               /* sqrt(NaN)=NaN, sqrt(+inf)=+inf
  42                                            sqrt(-inf)=sNaN */
  43     /* take care of zero and -ves */
  44         if(FLT_UWORD_IS_ZERO(hx)) return x;/* sqrt(+-0) = +-0 */
  45         if(ix<0) return (x-x)/(x-x);            /* sqrt(-ve) = sNaN */
  46
  47     /* normalize x */
  48         m = (ix>>23);
  49         if(FLT_UWORD_IS_SUBNORMAL(hx)) {                /* subnormal x */
  50             for(i=0;(ix&0x00800000L)==0;i++) ix<<=1;
  51             m -= i-1;
  52         }
  53         m -= 127;       /* unbias exponent */
  54         ix = (ix&0x007fffffL)|0x00800000L;
  55         if(m&1) /* odd m, double x to make it even */
  56             ix += ix;
  57         m >>= 1;        /* m = [m/2] */
  58
  59     /* generate sqrt(x) bit by bit */
  60         ix += ix;
  61         q = s = 0;              /* q = sqrt(x) */
  62         r = 0x01000000L;                /* r = moving bit from right to left */
  63
  64         while(r!=0) {
  65             t = s+r;
  66             if(t<=ix) {
  67                 s    = t+r;
  68                 ix  -= t;
  69                 q   += r;
  70             }
  71             ix += ix;
  72             r>>=1;
  73         }
  74
  75     /* use floating add to find out rounding direction */
  76         if(ix!=0) {
  77             z = one-tiny; /* trigger inexact flag */
  78             if (z>=one) {
  79                 z = one+tiny;
  80                 if (z>one)
  81                     q += 2;
  82                 else
  83                     q += (q&1);
  84             }
  85         }
  86         ix = (q>>1)+0x3f000000L;
  87         ix += (m <<23);
  88         SET_FLOAT_WORD(z,ix);
  89         return z;
  90 }