Quelle e_sqrtf.cpp Sprache: C

/* e_sqrtf.c -- float version of e_sqrt.c.
* Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
*/

/*
* ====================================================
* Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
*
* Developed at SunPro, a Sun Microsystems, Inc. business.
* Permission to use, copy, modify, and distribute this
* software is freely granted, provided that this notice
* is preserved.
* ====================================================
*/

//#ifndef lint
//static char rcsid[] = "$FreeBSD$";
//#endif

#include "math_private.h"

#ifdef USE_BUILTIN_SQRTF
float
__ieee754_sqrtf(float x)
{
return (__builtin_sqrtf(x));
}
#else
static const float one = 1.0, tiny=1.0e-30;

float
__ieee754_sqrtf(float x)
{
float z;
int32_t sign = (int)0x80000000;
int32_t ix,s,q,m,t,i;
u_int32_t r;

GET_FLOAT_WORD(ix,x);

    /* take care of Inf and NaN */
if((ix&0x7f800000)==0x7f800000) {
     return x*x+x;  /* sqrt(NaN)=NaN, sqrt(+inf)=+inf
   sqrt(-inf)=sNaN */
}
    /* take care of zero */
if(ix<=0) {
     if((ix&(~sign))==0) return x;/* sqrt(+-0) = +-0 */
     else if(ix<0)
  return (x-x)/(x-x);  /* sqrt(-ve) = sNaN */
}
    /* normalize x */
m = (ix>>23);
if(m==0) {    /* subnormal x */
     for(i=0;(ix&0x00800000)==0;i++) ix<<=1;
     m -= i-1;
}
m -= 127; /* unbias exponent */
ix = (ix&0x007fffff)|0x00800000;
if(m&1) /* odd m, double x to make it even */
     ix += ix;
m >>= 1; /* m = [m/2] */

    /* generate sqrt(x) bit by bit */
ix += ix;
q = s = 0;  /* q = sqrt(x) */
r = 0x01000000;  /* r = moving bit from right to left */

while(r!=0) {
     t = s+r;
     if(t<=ix) {
  s    = t+r;
  ix  -= t;
  q   += r;
     }
     ix += ix;
     r>>=1;
}

    /* use floating add to find out rounding direction */
if(ix!=0) {
     z = one-tiny; /* trigger inexact flag */
     if (z>=one) {
         z = one+tiny;
  if (z>one)
      q += 2;
  else
      q += (q&1);
     }
}
ix = (q>>1)+0x3f000000;
ix += (m <<23);
SET_FLOAT_WORD(z,ix);
return z;
}
#endif

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