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3362 | Serge | 1 | /* @(#)s_scalbn.c 5.1 93/09/24 */ |
2 | /* |
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3 | * ==================================================== |
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4 | * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. |
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5 | * |
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6 | * Developed at SunPro, a Sun Microsystems, Inc. business. |
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7 | * Permission to use, copy, modify, and distribute this |
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8 | * software is freely granted, provided that this notice |
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9 | * is preserved. |
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10 | * ==================================================== |
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11 | */ |
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12 | |||
13 | /* |
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14 | * scalbn (double x, int n) |
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15 | * scalbn(x,n) returns x* 2**n computed by exponent |
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16 | * manipulation rather than by actually performing an |
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17 | * exponentiation or a multiplication. |
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18 | */ |
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19 | |||
20 | #include "fdlibm.h" |
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21 | |||
22 | #ifndef _DOUBLE_IS_32BITS |
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23 | |||
24 | #ifdef __STDC__ |
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25 | static const double |
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26 | #else |
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27 | static double |
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28 | #endif |
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29 | two54 = 1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */ |
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30 | twom54 = 5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */ |
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31 | huge = 1.0e+300, |
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32 | tiny = 1.0e-300; |
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33 | |||
34 | #ifdef __STDC__ |
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35 | double scalbln (double x, long int n) |
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36 | #else |
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37 | double scalbln (x,n) |
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38 | double x; long int n; |
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39 | #endif |
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40 | { |
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41 | __int32_t k,hx,lx; |
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42 | EXTRACT_WORDS(hx,lx,x); |
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43 | k = (hx&0x7ff00000)>>20; /* extract exponent */ |
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44 | if (k==0) { /* 0 or subnormal x */ |
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45 | if ((lx|(hx&0x7fffffff))==0) return x; /* +-0 */ |
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46 | x *= two54; |
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47 | GET_HIGH_WORD(hx,x); |
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48 | k = ((hx&0x7ff00000)>>20) - 54; |
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49 | } |
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50 | if (k==0x7ff) return x+x; /* NaN or Inf */ |
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51 | k = k+n; |
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52 | if (n> 50000 || k > 0x7fe) |
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53 | return huge*copysign(huge,x); /* overflow */ |
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54 | if (n< -50000) return tiny*copysign(tiny,x); /*underflow*/ |
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55 | if (k > 0) /* normal result */ |
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56 | {SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20)); return x;} |
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57 | if (k <= -54) |
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58 | return tiny*copysign(tiny,x); /*underflow*/ |
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59 | k += 54; /* subnormal result */ |
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60 | SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20)); |
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61 | return x*twom54; |
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62 | } |
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63 | |||
64 | #endif /* _DOUBLE_IS_32BITS */20)); |