sysdeps/ieee754/flt-32/e_sqrtf.c

   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