[444] | 1 | |
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| 2 | /* @(#)z_expf.c 1.0 98/08/13 */ |
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| 3 | /****************************************************************** |
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| 4 | * The following routines are coded directly from the algorithms |
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| 5 | * and coefficients given in "Software Manual for the Elementary |
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| 6 | * Functions" by William J. Cody, Jr. and William Waite, Prentice |
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| 7 | * Hall, 1980. |
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| 8 | ******************************************************************/ |
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| 9 | /****************************************************************** |
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| 10 | * Exponential Function |
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| 11 | * |
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| 12 | * Input: |
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| 13 | * x - floating point value |
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| 14 | * |
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| 15 | * Output: |
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| 16 | * e raised to x. |
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| 17 | * |
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| 18 | * Description: |
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| 19 | * This routine returns e raised to the xth power. |
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| 20 | * |
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| 21 | *****************************************************************/ |
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| 22 | |
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| 23 | #include <float.h> |
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| 24 | #include "fdlibm.h" |
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| 25 | #include "zmath.h" |
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| 26 | |
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| 27 | static const float INV_LN2 = 1.442695040; |
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| 28 | static const float LN2 = 0.693147180; |
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| 29 | static const float p[] = { 0.249999999950, 0.00416028863 }; |
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| 30 | static const float q[] = { 0.5, 0.04998717878 }; |
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| 31 | |
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| 32 | float |
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| 33 | expf (float x) |
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| 34 | { |
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| 35 | int N; |
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| 36 | float g, z, R, P, Q; |
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| 37 | |
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| 38 | switch (numtestf (x)) |
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| 39 | { |
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| 40 | case NAN: |
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| 41 | errno = EDOM; |
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| 42 | return (x); |
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| 43 | case INF: |
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| 44 | errno = ERANGE; |
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| 45 | if (isposf (x)) |
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| 46 | return (z_infinity_f.f); |
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| 47 | else |
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| 48 | return (0.0); |
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| 49 | case 0: |
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| 50 | return (1.0); |
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| 51 | } |
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| 52 | |
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| 53 | /* Check for out of bounds. */ |
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| 54 | if (x > BIGX || x < SMALLX) |
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| 55 | { |
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| 56 | errno = ERANGE; |
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| 57 | return (x); |
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| 58 | } |
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| 59 | |
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| 60 | /* Check for a value too small to calculate. */ |
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| 61 | if (-z_rooteps_f < x && x < z_rooteps_f) |
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| 62 | { |
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| 63 | return (1.0); |
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| 64 | } |
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| 65 | |
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| 66 | /* Calculate the exponent. */ |
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| 67 | if (x < 0.0) |
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| 68 | N = (int) (x * INV_LN2 - 0.5); |
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| 69 | else |
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| 70 | N = (int) (x * INV_LN2 + 0.5); |
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| 71 | |
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| 72 | /* Construct the mantissa. */ |
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| 73 | g = x - N * LN2; |
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| 74 | z = g * g; |
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| 75 | P = g * (p[1] * z + p[0]); |
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| 76 | Q = q[1] * z + q[0]; |
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| 77 | R = 0.5 + P / (Q - P); |
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| 78 | |
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| 79 | /* Return the floating point value. */ |
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| 80 | N++; |
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| 81 | return (ldexpf (R, N)); |
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| 82 | } |
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| 83 | |
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| 84 | #ifdef _DOUBLE_IS_32BITS |
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| 85 | |
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| 86 | double exp (double x) |
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| 87 | { |
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| 88 | return (double) expf ((float) x); |
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| 89 | } |
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| 90 | |
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| 91 | #endif /* _DOUBLE_IS_32BITS */ |
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