| 1 | |
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| 2 | /* @(#)z_ldexp.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 | <<ldexp>>, <<ldexpf>>---load exponent |
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| 7 | |
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| 8 | INDEX |
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| 9 | ldexp |
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| 10 | INDEX |
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| 11 | ldexpf |
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| 12 | |
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| 13 | SYNOPSIS |
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| 14 | #include <math.h> |
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| 15 | double ldexp(double <[val]>, int <[exp]>); |
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| 16 | float ldexpf(float <[val]>, int <[exp]>); |
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| 17 | |
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| 18 | DESCRIPTION |
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| 19 | <<ldexp>> calculates the value |
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| 20 | @ifnottex |
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| 21 | <[val]> times 2 to the power <[exp]>. |
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| 22 | @end ifnottex |
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| 23 | @tex |
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| 24 | $val\times 2^{exp}$. |
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| 25 | @end tex |
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| 26 | <<ldexpf>> is identical, save that it takes and returns <<float>> |
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| 27 | rather than <<double>> values. |
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| 28 | |
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| 29 | RETURNS |
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| 30 | <<ldexp>> returns the calculated value. |
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| 31 | |
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| 32 | Underflow and overflow both set <<errno>> to <<ERANGE>>. |
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| 33 | On underflow, <<ldexp>> and <<ldexpf>> return 0.0. |
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| 34 | On overflow, <<ldexp>> returns plus or minus <<HUGE_VAL>>. |
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| 35 | |
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| 36 | PORTABILITY |
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| 37 | <<ldexp>> is ANSI. <<ldexpf>> is an extension. |
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| 38 | |
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| 39 | */ |
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| 40 | |
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| 41 | /****************************************************************** |
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| 42 | * ldexp |
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| 43 | * |
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| 44 | * Input: |
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| 45 | * d - a floating point value |
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| 46 | * e - an exponent value |
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| 47 | * |
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| 48 | * Output: |
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| 49 | * A floating point value f such that f = d * 2 ^ e. |
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| 50 | * |
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| 51 | * Description: |
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| 52 | * This function creates a floating point number f such that |
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| 53 | * f = d * 2 ^ e. |
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| 54 | * |
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| 55 | *****************************************************************/ |
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| 56 | |
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| 57 | #include <float.h> |
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| 58 | #include "fdlibm.h" |
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| 59 | #include "zmath.h" |
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| 60 | |
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| 61 | #ifndef _DOUBLE_IS_32BITS |
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| 62 | |
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| 63 | #define DOUBLE_EXP_OFFS 1023 |
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| 64 | |
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| 65 | double |
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| 66 | ldexp (double d, |
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| 67 | int e) |
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| 68 | { |
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| 69 | int exp; |
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| 70 | __uint32_t hd; |
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| 71 | |
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| 72 | GET_HIGH_WORD (hd, d); |
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| 73 | |
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| 74 | /* Check for special values and then scale d by e. */ |
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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 | errno = EDOM; |
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| 79 | break; |
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| 80 | |
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| 81 | case INF: |
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| 82 | errno = ERANGE; |
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| 83 | break; |
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| 84 | |
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| 85 | case 0: |
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| 86 | break; |
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| 87 | |
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| 88 | default: |
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| 89 | exp = (hd & 0x7ff00000) >> 20; |
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| 90 | exp += e; |
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| 91 | |
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| 92 | if (exp > DBL_MAX_EXP + DOUBLE_EXP_OFFS) |
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| 93 | { |
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| 94 | errno = ERANGE; |
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| 95 | d = z_infinity.d; |
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| 96 | } |
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| 97 | else if (exp < DBL_MIN_EXP + DOUBLE_EXP_OFFS) |
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| 98 | { |
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| 99 | errno = ERANGE; |
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| 100 | d = -z_infinity.d; |
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| 101 | } |
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| 102 | else |
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| 103 | { |
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| 104 | hd &= 0x800fffff; |
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| 105 | hd |= exp << 20; |
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| 106 | SET_HIGH_WORD (d, hd); |
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| 107 | } |
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| 108 | } |
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| 109 | |
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| 110 | return (d); |
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| 111 | } |
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| 112 | |
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| 113 | #endif /* _DOUBLE_IS_32BITS */ |
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