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28 /* atanh (x) = 0.5 * log ((1.0 + x)/(1.0 - x)) */
29 float atanhf (float x)
38 return (x > 0 ? INFINITY : -INFINITY);
45 /* Rearrange formula to avoid precision loss for small x.
47 atanh(x) = 0.5 * log ((1.0 + x)/(1.0 - x))
48 = 0.5 * log1p ((1.0 + x)/(1.0 - x) - 1.0)
49 = 0.5 * log1p ((1.0 + x - 1.0 + x) /(1.0 - x))
50 = 0.5 * log1p ((2.0 * x ) / (1.0 - x)) */
51 z = 0.5 * __fast_log1p ((z + z) / (1.0 - z));
52 return x >= 0 ? z : -z;