gonzui

    1: /* e_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 "math.h"
   17: #include "math_private.h"
   18: 
   19: static  const float      one  = 1.0, tiny=1.0e-30;
   20: 
   21: float
   22: sqrtf(float x)
   23: {
   24:         float z;
   25:         int32_t sign = (int)0x80000000; 
   26:         int32_t ix,s,q,m,t,i;
   27:         u_int32_t r;
   28: 
   29:         GET_FLOAT_WORD(ix,x);
   30: 
   31:     /* take care of Inf and NaN */
   32:         if((ix&0x7f800000)==0x7f800000) {                      
   33:             return x*x+x;              /* sqrt(NaN)=NaN, sqrt(+inf)=+inf
   34:                                            sqrt(-inf)=sNaN */
   35:         } 
   36:     /* take care of zero */
   37:         if(ix<=0) {
   38:             if((ix&(~sign))==0) return x;/* sqrt(+-0) = +-0 */
   39:             else if(ix<0)
   40:                 return (x-x)/(x-x);           /* sqrt(-ve) = sNaN */
   41:         }
   42:     /* normalize x */
   43:         m = (ix>>23);
   44:         if(m==0) {                             /* subnormal x */
   45:             for(i=0;(ix&0x00800000)==0;i++) ix<<=1;
   46:             m -= i-1;
   47:         }
   48:         m -= 127;      /* unbias exponent */
   49:         ix = (ix&0x007fffff)|0x00800000;
   50:         if(m&1)        /* odd m, double x to make it even */
   51:             ix += ix;
   52:         m >>= 1;       /* m = [m/2] */
   53: 
   54:     /* generate sqrt(x) bit by bit */
   55:         ix += ix;
   56:         q = s = 0;             /* q = sqrt(x) */
   57:         r = 0x01000000;                /* r = moving bit from right to left */
   58: 
   59:         while(r!=0) {
   60:             t = s+r; 
   61:             if(t<=ix) { 
   62:                 s    = t+r; 
   63:                 ix  -= t; 
   64:                 q   += r; 
   65:             } 
   66:             ix += ix;
   67:             r>>=1;
   68:         }
   69: 
   70:     /* use floating add to find out rounding direction */
   71:         if(ix!=0) {
   72:             z = one-tiny; /* trigger inexact flag */
   73:             if (z>=one) {
   74:                 z = one+tiny;
   75:                 if (z>one)
   76:                     q += 2;
   77:                 else
   78:                     q += (q&1);
   79:             }
   80:         }
   81:         ix = (q>>1)+0x3f000000;
   82:         ix += (m <<23);
   83:         SET_FLOAT_WORD(z,ix);
   84:         return z;
   85: }