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glibc  2.9
Functions | Variables
e_sqrtf.c File Reference
#include "math.h"
#include "math_private.h"

Go to the source code of this file.

Functions

float __ieee754_sqrtf (float x)

Variables

static float one = 1.0
static float tiny = 1.0e-30

Function Documentation

float __ieee754_sqrtf ( float  x)

Definition at line 32 of file e_sqrtf.c.

{
       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;
}

Variable Documentation

float one = 1.0 [static]

Definition at line 26 of file e_sqrtf.c.

float tiny = 1.0e-30 [static]

Definition at line 26 of file e_sqrtf.c.