| 1 | |
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| 2 | /* @(#)z_tanf.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 | * Tangent |
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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 | * tangent of x |
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| 17 | * |
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| 18 | * Description: |
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| 19 | * This routine calculates the tangent of x. |
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| 20 | * |
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| 21 | *****************************************************************/ |
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| 22 | |
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| 23 | #include "fdlibm.h" |
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| 24 | #include "zmath.h" |
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| 25 | |
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| 26 | static const float TWO_OVER_PI = 0.6366197723; |
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| 27 | static const float p[] = { -0.958017723e-1 }; |
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| 28 | static const float q[] = { -0.429135777, |
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| 29 | 0.971685835e-2 }; |
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| 30 | |
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| 31 | float |
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| 32 | tanf (float x) |
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| 33 | { |
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| 34 | float y, f, g, XN, xnum, xden, res; |
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| 35 | int N; |
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| 36 | |
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| 37 | /* Check for special values. */ |
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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 = EDOM; |
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| 45 | return (z_notanum_f.f); |
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| 46 | } |
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| 47 | |
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| 48 | y = fabsf (x); |
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| 49 | |
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| 50 | /* Check for values that are out of our range. */ |
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| 51 | if (y > 105414357.0) |
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| 52 | { |
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| 53 | errno = ERANGE; |
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| 54 | return (y); |
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| 55 | } |
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| 56 | |
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| 57 | if (x < 0.0) |
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| 58 | N = (int) (x * TWO_OVER_PI - 0.5); |
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| 59 | else |
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| 60 | N = (int) (x * TWO_OVER_PI + 0.5); |
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| 61 | |
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| 62 | XN = (float) N; |
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| 63 | |
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| 64 | f = x - N * __PI_OVER_TWO; |
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| 65 | |
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| 66 | /* Check for values that are too small. */ |
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| 67 | if (-z_rooteps_f < f && f < z_rooteps_f) |
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| 68 | { |
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| 69 | xnum = f; |
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| 70 | xden = 1.0; |
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| 71 | } |
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| 72 | |
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| 73 | /* Calculate the polynomial. */ |
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| 74 | else |
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| 75 | { |
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| 76 | g = f * f; |
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| 77 | |
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| 78 | xnum = f * (p[0] * g) + f; |
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| 79 | xden = (q[1] * g + q[0]) * g + 1.0; |
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| 80 | } |
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| 81 | |
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| 82 | /* Check for odd or even values. */ |
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| 83 | if (N & 1) |
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| 84 | { |
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| 85 | xnum = -xnum; |
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| 86 | res = xden / xnum; |
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| 87 | } |
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| 88 | else |
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| 89 | { |
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| 90 | res = xnum / xden; |
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| 91 | } |
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| 92 | |
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| 93 | return (res); |
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| 94 | } |
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| 95 | |
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| 96 | #ifdef _DOUBLE_IS_32BITS |
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| 97 | |
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| 98 | double tan (double x) |
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| 99 | { |
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| 100 | return (double) tanf ((float) x); |
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| 101 | } |
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| 102 | |
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| 103 | #endif /* _DOUBLE_IS_32BITS */ |
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