1  /* e_sqrtf.c -- float version of e_sqrt.c.
       2   */
       3  
       4  /*
       5   * ====================================================
       6   * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
       7   *
       8   * Developed at SunPro, a Sun Microsystems, Inc. business.
       9   * Permission to use, copy, modify, and distribute this
      10   * software is freely granted, provided that this notice
      11   * is preserved.
      12   * ====================================================
      13   */
      14  
      15  #include <math.h>
      16  #include <math_private.h>
      17  #include <libm-alias-finite.h>
      18  #include <math-use-builtins.h>
      19  
      20  float
      21  __ieee754_sqrtf(float x)
      22  {
      23  #if USE_SQRTF_BUILTIN
      24  	return __builtin_sqrtf (x);
      25  #else
      26  	/* Use generic implementation.  */
      27  	float z;
      28  	int32_t sign = (int)0x80000000;
      29  	int32_t ix,s,q,m,t,i;
      30  	uint32_t r;
      31  
      32  	GET_FLOAT_WORD(ix,x);
      33  
      34      /* take care of Inf and NaN */
      35  	if((ix&0x7f800000)==0x7f800000) {
      36  	    return x*x+x;		/* sqrt(NaN)=NaN, sqrt(+inf)=+inf
      37  					   sqrt(-inf)=sNaN */
      38  	}
      39      /* take care of zero */
      40  	if(ix<=0) {
      41  	    if((ix&(~sign))==0) return x;/* sqrt(+-0) = +-0 */
      42  	    else if(ix<0)
      43  		return (x-x)/(x-x);		/* sqrt(-ve) = sNaN */
      44  	}
      45      /* normalize x */
      46  	m = (ix>>23);
      47  	if(m==0) {				/* subnormal x */
      48  	    for(i=0;(ix&0x00800000)==0;i++) ix<<=1;
      49  	    m -= i-1;
      50  	}
      51  	m -= 127;	/* unbias exponent */
      52  	ix = (ix&0x007fffff)|0x00800000;
      53  	if(m&1)	/* odd m, double x to make it even */
      54  	    ix += ix;
      55  	m >>= 1;	/* m = [m/2] */
      56  
      57      /* generate sqrt(x) bit by bit */
      58  	ix += ix;
      59  	q = s = 0;		/* q = sqrt(x) */
      60  	r = 0x01000000;		/* r = moving bit from right to left */
      61  
      62  	while(r!=0) {
      63  	    t = s+r;
      64  	    if(t<=ix) {
      65  		s    = t+r;
      66  		ix  -= t;
      67  		q   += r;
      68  	    }
      69  	    ix += ix;
      70  	    r>>=1;
      71  	}
      72  
      73      /* use floating add to find out rounding direction */
      74  	if(ix!=0) {
      75  	    z = 0x1p0 - 0x1.4484cp-100; /* trigger inexact flag.  */
      76  	    if (z >= 0x1p0) {
      77  		z = 0x1p0 + 0x1.4484cp-100;
      78  		if (z > 0x1p0)
      79  		    q += 2;
      80  		else
      81  		    q += (q&1);
      82  	    }
      83  	}
      84  	ix = (q>>1)+0x3f000000;
      85  	ix += (m <<23);
      86  	SET_FLOAT_WORD(z,ix);
      87  	return z;
      88  #endif /* ! USE_SQRTF_BUILTIN  */
      89  }
      90  #ifndef __ieee754_sqrtf
      91  libm_alias_finite (__ieee754_sqrtf, __sqrtf)
      92  #endif