logaddexp.h

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/*
 * logaddexp, adapted from numpy/core/src/npymath/npy_math.c.src.
 *
 * Copyright (c) 2005-2011, NumPy Developers.
 * All rights reserved.
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 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 *
 *     * Redistributions of source code must retain the above copyright
 *        notice, this list of conditions and the following disclaimer.
 *
 *     * Redistributions in binary form must reproduce the above
 *        copyright notice, this list of conditions and the following
 *        disclaimer in the documentation and/or other materials provided
 *        with the distribution.
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 */
 
 
static double logaddexp(double x, double y)
{
    const double tmp = x - y;
    if (tmp > 0) {
        return x + log1p(exp(-tmp));
    }
    else if (tmp <= 0) {
        return y + log1p(exp(tmp));
    }
    else {
        /* NaNs, or infinities of the same sign involved */
        return x + y;
    }
}