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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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