| 1 | /* e_sqrtf.c -- float version of e_sqrt.c.
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| 2 | * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
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| 3 | */
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| 4 |
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| 5 | /*
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| 6 | * ====================================================
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| 7 | * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
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| 8 | *
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| 9 | * Developed at SunPro, a Sun Microsystems, Inc. business.
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| 10 | * Permission to use, copy, modify, and distribute this
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| 11 | * software is freely granted, provided that this notice
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| 12 | * is preserved.
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| 13 | * ====================================================
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| 14 | */
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| 15 |
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| 16 | #ifndef lint
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| 17 | static char rcsid[] = "$FreeBSD: src/lib/msun/src/e_sqrtf.c,v 1.7 2002/05/28 18:15:04 alfred Exp $";
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| 18 | #endif
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| 19 |
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| 20 | #include "math.h"
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| 21 | #include "math_private.h"
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| 22 |
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| 23 | static const float one = 1.0, tiny=1.0e-30;
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| 24 |
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| 25 | float
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| 26 | __ieee754_sqrtf(float x)
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| 27 | {
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| 28 | float z;
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| 29 | int32_t sign = (int)0x80000000;
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| 30 | int32_t ix,s,q,m,t,i;
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| 31 | u_int32_t r;
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| 32 |
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| 33 | GET_FLOAT_WORD(ix,x);
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| 34 |
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| 35 | /* take care of Inf and NaN */
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| 36 | if((ix&0x7f800000)==0x7f800000) {
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| 37 | return x*x+x; /* sqrt(NaN)=NaN, sqrt(+inf)=+inf
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| 38 | sqrt(-inf)=sNaN */
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| 39 | }
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| 40 | /* take care of zero */
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| 41 | if(ix<=0) {
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| 42 | if((ix&(~sign))==0) return x;/* sqrt(+-0) = +-0 */
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| 43 | else if(ix<0)
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| 44 | return (x-x)/(x-x); /* sqrt(-ve) = sNaN */
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| 45 | }
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| 46 | /* normalize x */
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| 47 | m = (ix>>23);
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| 48 | if(m==0) { /* subnormal x */
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| 49 | for(i=0;(ix&0x00800000)==0;i++) ix<<=1;
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| 50 | m -= i-1;
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| 51 | }
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| 52 | m -= 127; /* unbias exponent */
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| 53 | ix = (ix&0x007fffff)|0x00800000;
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| 54 | if(m&1) /* odd m, double x to make it even */
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| 55 | ix += ix;
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| 56 | m >>= 1; /* m = [m/2] */
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| 57 |
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| 58 | /* generate sqrt(x) bit by bit */
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| 59 | ix += ix;
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| 60 | q = s = 0; /* q = sqrt(x) */
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| 61 | r = 0x01000000; /* r = moving bit from right to left */
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| 62 |
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| 63 | while(r!=0) {
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| 64 | t = s+r;
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| 65 | if(t<=ix) {
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| 66 | s = t+r;
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| 67 | ix -= t;
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| 68 | q += r;
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| 69 | }
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| 70 | ix += ix;
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| 71 | r>>=1;
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| 72 | }
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| 73 |
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| 74 | /* use floating add to find out rounding direction */
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| 75 | if(ix!=0) {
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| 76 | z = one-tiny; /* trigger inexact flag */
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| 77 | if (z>=one) {
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| 78 | z = one+tiny;
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| 79 | if (z>one)
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| 80 | q += 2;
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| 81 | else
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| 82 | q += (q&1);
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| 83 | }
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| 84 | }
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| 85 | ix = (q>>1)+0x3f000000;
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| 86 | ix += (m <<23);
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| 87 | SET_FLOAT_WORD(z,ix);
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| 88 | return z;
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| 89 | }
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