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[/] [or1k/] [trunk/] [newlib/] [newlib/] [libm/] [math/] [ef_sqrt.c] - Blame information for rev 1767

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1 39 lampret 
/* ef_sqrtf.c -- float version of e_sqrt.c.
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 * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
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 */
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/*
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 * ====================================================
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 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
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 *
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 * Developed at SunPro, a Sun Microsystems, Inc. business.
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 * Permission to use, copy, modify, and distribute this
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 * software is freely granted, provided that this notice
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 * is preserved.
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 * ====================================================
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 */
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#include "fdlibm.h"
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#ifdef __STDC__
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static  const float     one     = 1.0, tiny=1.0e-30;
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#else
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static  float   one     = 1.0, tiny=1.0e-30;
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#endif
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#ifdef __STDC__
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        float __ieee754_sqrtf(float x)
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#else
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        float __ieee754_sqrtf(x)
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        float x;
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#endif
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{
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        float z;
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        __int32_t       sign = (__int32_t)0x80000000;
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        __uint32_t r;
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        __int32_t ix,s,q,m,t,i;
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        GET_FLOAT_WORD(ix,x);
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    /* take care of Inf and NaN */
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        if((ix&0x7f800000L)==0x7f800000L) {
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            return x*x+x;               /* sqrt(NaN)=NaN, sqrt(+inf)=+inf
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                                           sqrt(-inf)=sNaN */
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        }
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    /* take care of zero */
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        if(ix<=0) {
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            if((ix&(~sign))==0) return x;/* sqrt(+-0) = +-0 */
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            else if(ix<0)
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                return (x-x)/(x-x);             /* sqrt(-ve) = sNaN */
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        }
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    /* normalize x */
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        m = (ix>>23);
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        if(m==0) {                               /* subnormal x */
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            for(i=0;(ix&0x00800000L)==0;i++) ix<<=1;
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            m -= i-1;
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        }
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        m -= 127;       /* unbias exponent */
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        ix = (ix&0x007fffffL)|0x00800000L;
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        if(m&1) /* odd m, double x to make it even */
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            ix += ix;
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        m >>= 1;        /* m = [m/2] */
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    /* generate sqrt(x) bit by bit */
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        ix += ix;
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        q = s = 0;               /* q = sqrt(x) */
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        r = 0x01000000L;                /* r = moving bit from right to left */
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        while(r!=0) {
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            t = s+r;
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            if(t<=ix) {
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                s    = t+r;
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                ix  -= t;
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                q   += r;
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            }
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            ix += ix;
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            r>>=1;
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        }
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    /* use floating add to find out rounding direction */
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        if(ix!=0) {
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            z = one-tiny; /* trigger inexact flag */
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            if (z>=one) {
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                z = one+tiny;
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                if (z>one)
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                    q += 2;
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                else
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                    q += (q&1);
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            }
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        }
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        ix = (q>>1)+0x3f000000L;
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        ix += (m <<23);
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        SET_FLOAT_WORD(z,ix);
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        return z;
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}

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