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4349 | Serge | 1 | /* ef_sqrtf.c -- float version of e_sqrt.c. |
2 | * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com. |
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3 | */ |
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4 | |||
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 | |||
16 | #include "fdlibm.h" |
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17 | |||
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 | |||
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 | |||
35 | GET_FLOAT_WORD(ix,x); |
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36 | hx = ix&0x7fffffff; |
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37 | |||
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 | |||
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 | |||
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 | |||
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 | |||
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 | }23); |