sec.c

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/*-
 * Copyright (c) 2014-2018 Carsten Sonne Larsen <cs@innolan.net>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. 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.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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 */

/**
 * @file  ver.c
 * @brief Secant function
 */

#include "prim.h"

/**
 * @brief   Secant function
 * @details
 * <pre>
 * sec(x) = 1/cos(x)
 *        = 1/sqrt(cos(x)*cos(x))
 * </pre>
 */
double sec(double x)
{
    double a, b, c;

    a = cos(x);
    if (a == 0.0)
    {
        return NAN;
    }

    b = sqrt(a * a);
    c = 1.0 / b;

    return c;
}