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1 //=========================================================================== |
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2 // |
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3 // s_scalbn.c |
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4 // |
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5 // Part of the standard mathematical function library |
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6 // |
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7 //=========================================================================== |
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8 //####COPYRIGHTBEGIN#### |
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9 // |
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10 // ------------------------------------------- |
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11 // The contents of this file are subject to the Cygnus eCos Public License |
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12 // Version 1.0 (the "License"); you may not use this file except in |
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13 // compliance with the License. You may obtain a copy of the License at |
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14 // http://sourceware.cygnus.com/ecos |
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15 // |
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16 // Software distributed under the License is distributed on an "AS IS" |
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17 // basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See the |
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18 // License for the specific language governing rights and limitations under |
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19 // the License. |
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20 // |
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21 // The Original Code is eCos - Embedded Cygnus Operating System, released |
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22 // September 30, 1998. |
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23 // |
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24 // The Initial Developer of the Original Code is Cygnus. Portions created |
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25 // by Cygnus are Copyright (C) 1998 Cygnus Solutions. All Rights Reserved. |
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26 // ------------------------------------------- |
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27 // |
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28 //####COPYRIGHTEND#### |
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29 //=========================================================================== |
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30 //#####DESCRIPTIONBEGIN#### |
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31 // |
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32 // Author(s): jlarmour@cygnus.co.uk |
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33 // Contributors: jlarmour@cygnus.co.uk |
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34 // Date: 1998-02-13 |
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35 // Purpose: |
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36 // Description: |
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37 // Usage: |
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38 // |
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39 //####DESCRIPTIONEND#### |
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40 // |
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41 //=========================================================================== |
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42 |
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43 // CONFIGURATION |
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44 |
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45 #include <pkgconf/libm.h> // Configuration header |
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46 |
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47 // Include the Math library? |
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48 #ifdef CYGPKG_LIBM |
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49 |
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50 // Derived from code with the following copyright |
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51 |
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52 |
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53 /* @(#)s_scalbn.c 1.3 95/01/18 */ |
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54 /* |
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55 * ==================================================== |
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56 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. |
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57 * |
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58 * Developed at SunSoft, a Sun Microsystems, Inc. business. |
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59 * Permission to use, copy, modify, and distribute this |
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60 * software is freely granted, provided that this notice |
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61 * is preserved. |
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62 * ==================================================== |
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63 */ |
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64 |
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65 /* |
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66 * scalbn (double x, int n) |
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67 * scalbn(x,n) returns x* 2**n computed by exponent |
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68 * manipulation rather than by actually performing an |
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69 * exponentiation or a multiplication. |
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70 */ |
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71 |
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72 #include "mathincl/fdlibm.h" |
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73 |
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74 static const double |
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75 two54 = 1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */ |
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76 twom54 = 5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */ |
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77 huge = 1.0e+300, |
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78 tiny = 1.0e-300; |
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79 |
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80 double scalbn (double x, int n) |
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81 { |
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82 int k,hx,lx; |
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83 hx = CYG_LIBM_HI(x); |
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84 lx = CYG_LIBM_LO(x); |
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85 k = (hx&0x7ff00000)>>20; /* extract exponent */ |
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86 if (k==0) { /* 0 or subnormal x */ |
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87 if ((lx|(hx&0x7fffffff))==0) return x; /* +-0 */ |
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88 x *= two54; |
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89 hx = CYG_LIBM_HI(x); |
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90 k = ((hx&0x7ff00000)>>20) - 54; |
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91 if (n< -50000) return tiny*x; /*underflow*/ |
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92 } |
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93 if (k==0x7ff) return x+x; /* NaN or Inf */ |
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94 k = k+n; |
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95 if (k > 0x7fe) return huge*copysign(huge,x); /* overflow */ |
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96 if (k > 0) /* normal result */ |
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97 {CYG_LIBM_HI(x) = (hx&0x800fffff)|(k<<20); return x;} |
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98 if (k <= -54) { |
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99 if (n > 50000) /* in case integer overflow in n+k */ |
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100 return huge*copysign(huge,x); /*overflow*/ |
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101 else return tiny*copysign(tiny,x); /*underflow*/ |
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102 } |
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103 k += 54; /* subnormal result */ |
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104 CYG_LIBM_HI(x) = (hx&0x800fffff)|(k<<20); |
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105 return x*twom54; |
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106 } |
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107 |
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108 #endif // ifdef CYGPKG_LIBM |
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109 |
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110 // EOF s_scalbn.c |
