| 1 | /* ef_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 | #include "fdlibm.h" |
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| 17 | |
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| 18 | #ifdef __STDC__ |
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| 19 | static const float one = 1.0, tiny=1.0e-30; |
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| 20 | #else |
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| 21 | static float one = 1.0, tiny=1.0e-30; |
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| 22 | #endif |
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| 23 | |
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| 24 | #ifdef __STDC__ |
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| 25 | float __ieee754_sqrtf(float x) |
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| 26 | #else |
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| 27 | float __ieee754_sqrtf(x) |
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| 28 | float x; |
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| 29 | #endif |
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| 30 | { |
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| 31 | float z; |
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| 32 | __uint32_t r,hx; |
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| 33 | __int32_t ix,s,q,m,t,i; |
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| 34 | |
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| 35 | GET_FLOAT_WORD(ix,x); |
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| 36 | hx = ix&0x7fffffff; |
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| 37 | |
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| 38 | /* take care of Inf and NaN */ |
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| 39 | if(!FLT_UWORD_IS_FINITE(hx)) |
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| 40 | return x*x+x; /* sqrt(NaN)=NaN, sqrt(+inf)=+inf |
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| 41 | sqrt(-inf)=sNaN */ |
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| 42 | /* take care of zero and -ves */ |
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| 43 | if(FLT_UWORD_IS_ZERO(hx)) return x;/* sqrt(+-0) = +-0 */ |
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| 44 | if(ix<0) 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(FLT_UWORD_IS_SUBNORMAL(hx)) { /* subnormal x */ |
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| 49 | for(i=0;(ix&0x00800000L)==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&0x007fffffL)|0x00800000L; |
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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 = 0x01000000L; /* 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)+0x3f000000L; |
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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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