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| Rev | Author | Line No. | Line |
|---|---|---|---|
| 1906 | serge | 1 | #include |
| 2 | #include |
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| 3 | #include "fastmath.h" |
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| 4 | |||
| 5 | /* atanh (x) = 0.5 * log ((1.0 + x)/(1.0 - x)) */ |
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| 6 | float atanhf (float x) |
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| 7 | { |
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| 8 | float z; |
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| 9 | if isnan (x) |
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| 10 | return x; |
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| 11 | z = fabsf (x); |
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| 12 | if (z == 1.0) |
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| 13 | { |
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| 14 | errno = ERANGE; |
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| 15 | return (x > 0 ? INFINITY : -INFINITY); |
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| 16 | } |
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| 17 | if ( z > 1.0) |
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| 18 | { |
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| 19 | errno = EDOM; |
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| 20 | return nanf(""); |
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| 21 | } |
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| 22 | /* Rearrange formula to avoid precision loss for small x. |
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| 23 | |||
| 24 | atanh(x) = 0.5 * log ((1.0 + x)/(1.0 - x)) |
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| 25 | = 0.5 * log1p ((1.0 + x)/(1.0 - x) - 1.0) |
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| 26 | = 0.5 * log1p ((1.0 + x - 1.0 + x) /(1.0 - x)) |
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| 27 | = 0.5 * log1p ((2.0 * x ) / (1.0 - x)) */ |
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| 28 | z = 0.5 * __fast_log1p ((z + z) / (1.0 - z)); |
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| 29 | return x >= 0 ? z : -z; |
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| 30 | } |