1 | |
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2 | /* @(#)z_frexp.c 1.0 98/08/13 */ |
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3 | |
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4 | /* |
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5 | FUNCTION |
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6 | <<frexp>>, <<frexpf>>---split floating-point number |
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7 | INDEX |
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8 | frexp |
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9 | INDEX |
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10 | frexpf |
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11 | |
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12 | SYNOPSIS |
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13 | #include <math.h> |
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14 | double frexp(double <[val]>, int *<[exp]>); |
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15 | float frexpf(float <[val]>, int *<[exp]>); |
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16 | |
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17 | DESCRIPTION |
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18 | All nonzero, normal numbers can be described as <[m]> * 2**<[p]>. |
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19 | <<frexp>> represents the double <[val]> as a mantissa <[m]> |
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20 | and a power of two <[p]>. The resulting mantissa will always |
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21 | be greater than or equal to <<0.5>>, and less than <<1.0>> (as |
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22 | long as <[val]> is nonzero). The power of two will be stored |
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23 | in <<*>><[exp]>. |
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24 | |
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25 | @ifnottex |
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26 | <[m]> and <[p]> are calculated so that |
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27 | <[val]> is <[m]> times <<2>> to the power <[p]>. |
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28 | @end ifnottex |
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29 | @tex |
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30 | <[m]> and <[p]> are calculated so that |
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31 | $ val = m \times 2^p $. |
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32 | @end tex |
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33 | |
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34 | <<frexpf>> is identical, other than taking and returning |
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35 | floats rather than doubles. |
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36 | |
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37 | RETURNS |
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38 | <<frexp>> returns the mantissa <[m]>. If <[val]> is <<0>>, infinity, |
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39 | or Nan, <<frexp>> will set <<*>><[exp]> to <<0>> and return <[val]>. |
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40 | |
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41 | PORTABILITY |
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42 | <<frexp>> is ANSI. |
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43 | <<frexpf>> is an extension. |
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44 | |
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45 | |
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46 | */ |
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47 | |
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48 | /***************************************************************** |
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49 | * frexp |
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50 | * |
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51 | * Input: |
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52 | * d - floating point value |
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53 | * exp - exponent value |
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54 | * |
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55 | * Output: |
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56 | * A floating point value in the range [0.5, 1). |
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57 | * |
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58 | * Description: |
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59 | * This routine breaks a floating point value into a number f and |
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60 | * an exponent exp such that d = f * 2 ^ exp. |
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61 | * |
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62 | *****************************************************************/ |
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63 | |
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64 | #include "fdlibm.h" |
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65 | #include "zmath.h" |
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66 | |
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67 | #ifndef _DOUBLE_IS_32BITS |
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68 | |
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69 | double frexp (double d, int *exp) |
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70 | { |
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71 | double f; |
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72 | __uint32_t hd, ld, hf, lf; |
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73 | |
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74 | /* Check for special values. */ |
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75 | switch (numtest (d)) |
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76 | { |
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77 | case NAN: |
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78 | case INF: |
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79 | errno = EDOM; |
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80 | case 0: |
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81 | *exp = 0; |
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82 | return (d); |
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83 | } |
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84 | |
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85 | EXTRACT_WORDS (hd, ld, d); |
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86 | |
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87 | /* Get the exponent. */ |
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88 | *exp = ((hd & 0x7ff00000) >> 20) - 1022; |
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89 | |
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90 | /* Get the mantissa. */ |
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91 | lf = ld; |
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92 | hf = hd & 0x800fffff; |
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93 | hf |= 0x3fe00000; |
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94 | |
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95 | INSERT_WORDS (f, hf, lf); |
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96 | |
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97 | return (f); |
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98 | } |
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99 | |
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100 | #endif /* _DOUBLE_IS_32BITS */ |
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