1 | |
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2 | /* @(#)s_frexp.c 5.1 93/09/24 */ |
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3 | /* |
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4 | * ==================================================== |
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5 | * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. |
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6 | * |
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7 | * Developed at SunPro, a Sun Microsystems, Inc. business. |
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8 | * Permission to use, copy, modify, and distribute this |
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9 | * software is freely granted, provided that this notice |
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10 | * is preserved. |
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11 | * ==================================================== |
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12 | */ |
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13 | |
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14 | /* |
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15 | FUNCTION |
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16 | <<frexp>>, <<frexpf>>---split floating-point number |
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17 | INDEX |
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18 | frexp |
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19 | INDEX |
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20 | frexpf |
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21 | |
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22 | SYNOPSIS |
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23 | #include <math.h> |
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24 | double frexp(double <[val]>, int *<[exp]>); |
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25 | float frexpf(float <[val]>, int *<[exp]>); |
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26 | |
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27 | DESCRIPTION |
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28 | All nonzero, normal numbers can be described as <[m]> * 2**<[p]>. |
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29 | <<frexp>> represents the double <[val]> as a mantissa <[m]> |
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30 | and a power of two <[p]>. The resulting mantissa will always |
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31 | be greater than or equal to <<0.5>>, and less than <<1.0>> (as |
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32 | long as <[val]> is nonzero). The power of two will be stored |
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33 | in <<*>><[exp]>. |
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34 | |
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35 | @ifnottex |
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36 | <[m]> and <[p]> are calculated so that |
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37 | <[val]> is <[m]> times <<2>> to the power <[p]>. |
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38 | @end ifnottex |
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39 | @tex |
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40 | <[m]> and <[p]> are calculated so that |
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41 | $ val = m \times 2^p $. |
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42 | @end tex |
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43 | |
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44 | <<frexpf>> is identical, other than taking and returning |
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45 | floats rather than doubles. |
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46 | |
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47 | RETURNS |
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48 | <<frexp>> returns the mantissa <[m]>. If <[val]> is <<0>>, infinity, |
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49 | or Nan, <<frexp>> will set <<*>><[exp]> to <<0>> and return <[val]>. |
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50 | |
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51 | PORTABILITY |
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52 | <<frexp>> is ANSI. |
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53 | <<frexpf>> is an extension. |
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54 | |
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55 | |
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56 | */ |
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57 | |
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58 | /* |
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59 | * for non-zero x |
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60 | * x = frexp(arg,&exp); |
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61 | * return a double fp quantity x such that 0.5 <= |x| <1.0 |
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62 | * and the corresponding binary exponent "exp". That is |
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63 | * arg = x*2^exp. |
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64 | * If arg is inf, 0.0, or NaN, then frexp(arg,&exp) returns arg |
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65 | * with *exp=0. |
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66 | */ |
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67 | |
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68 | #include "fdlibm.h" |
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69 | |
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70 | #ifndef _DOUBLE_IS_32BITS |
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71 | |
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72 | #ifdef __STDC__ |
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73 | static const double |
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74 | #else |
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75 | static double |
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76 | #endif |
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77 | two54 = 1.80143985094819840000e+16; /* 0x43500000, 0x00000000 */ |
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78 | |
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79 | #ifdef __STDC__ |
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80 | double frexp(double x, int *eptr) |
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81 | #else |
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82 | double frexp(x, eptr) |
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83 | double x; int *eptr; |
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84 | #endif |
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85 | { |
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86 | __int32_t hx, ix, lx; |
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87 | EXTRACT_WORDS(hx,lx,x); |
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88 | ix = 0x7fffffff&hx; |
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89 | *eptr = 0; |
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90 | if(ix>=0x7ff00000||((ix|lx)==0)) return x; /* 0,inf,nan */ |
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91 | if (ix<0x00100000) { /* subnormal */ |
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92 | x *= two54; |
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93 | GET_HIGH_WORD(hx,x); |
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94 | ix = hx&0x7fffffff; |
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95 | *eptr = -54; |
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96 | } |
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97 | *eptr += (ix>>20)-1022; |
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98 | hx = (hx&0x800fffff)|0x3fe00000; |
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99 | SET_HIGH_WORD(x,hx); |
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100 | return x; |
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101 | } |
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102 | |
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103 | #endif /* _DOUBLE_IS_32BITS */ |
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