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25c28e83beb90e7c80452a7c818c5e6f73a07dc8Piotr Jasiukajtis * Copyright 2011 Nexenta Systems, Inc. All rights reserved.
25c28e83beb90e7c80452a7c818c5e6f73a07dc8Piotr Jasiukajtis * Copyright 2006 Sun Microsystems, Inc. All rights reserved.
25c28e83beb90e7c80452a7c818c5e6f73a07dc8Piotr Jasiukajtis * Use is subject to license terms.
25c28e83beb90e7c80452a7c818c5e6f73a07dc8Piotr Jasiukajtis * ATANH(x) = --- * LOG(1 + -------) = 0.5 * LOG1P(2 * --------)
25c28e83beb90e7c80452a7c818c5e6f73a07dc8Piotr Jasiukajtis * 2 1 - x 1 - x
25c28e83beb90e7c80452a7c818c5e6f73a07dc8Piotr Jasiukajtis * Note: to guarantee ATANH(-x) = -ATANH(x), we use
ddc0e0b53c661f6e439e3b7072b3ef353eadb4afRichard Lowe * sign(x) |x|
25c28e83beb90e7c80452a7c818c5e6f73a07dc8Piotr Jasiukajtis * ATANH(x) = ------- * LOG1P(2*-------).
25c28e83beb90e7c80452a7c818c5e6f73a07dc8Piotr Jasiukajtis * Special cases:
25c28e83beb90e7c80452a7c818c5e6f73a07dc8Piotr Jasiukajtis * ATANH(x) is NaN if |x| > 1 with signal;
25c28e83beb90e7c80452a7c818c5e6f73a07dc8Piotr Jasiukajtis * ATANH(NaN) is that NaN with no signal;
25c28e83beb90e7c80452a7c818c5e6f73a07dc8Piotr Jasiukajtis * ATANH(+-1) is +-INF with signal.