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  /*
   * Copyright (C) 2015 INRIA
   *
   * This file is subject to the terms and conditions of the GNU Lesser
   * General Public License v2.1. See the file LICENSE in the top level
   * directory for more details.
   */
  
  /**
   * @defgroup    sys_bitfield Bitfields
   * @ingroup     sys
   * @brief       Bitfields of arbitrary length
   * @file
   * @{
   *
   * @brief       bitfields operations on bitfields of arbitrary length
   *
   * @note        Code taken mostly from
   *              <a href="http://stackoverflow.com/questions/1590893/error-trying-to-define-a-1-024-bit-128-byte-bit-field">
   *              Stackoverflow, User Christoph</a>
   *
   * @author      Oliver Hahm <oliver.hahm@inria.fr>
   */
  
  #ifndef BITFIELD_H
  #define BITFIELD_H
  
  #include <stdint.h>
  #include <stdbool.h>
  #include <stddef.h>
  
  #ifdef __cplusplus
  extern "C" {
  #endif
  
  /**
   * @brief   Declare a bitfield of a given size
   *
   * @note    SIZE should be a constant expression. This avoids variable length
   *          arrays.
   */
  #define BITFIELD(NAME, SIZE)  uint8_t NAME[((SIZE) + 7) / 8]
  
  /**
   * @brief   Set the bit to 1
   *
   * @param[in,out] field The bitfield
   * @param[in]     idx   The number of the bit to set
   */
  static inline void bf_set(uint8_t field[], size_t idx)
  {
      field[idx / 8] |= (1u << (idx % 8));
  }
  
  /**
   * @brief   Clear the bit
   *
   * @param[in,out] field The bitfield
   * @param[in]     idx   The number of the bit to clear
   */
  static inline void bf_unset(uint8_t field[], size_t idx)
  {
      field[idx / 8] &= ~(1u << (idx % 8));
  }
  
  /**
   * @brief   Toggle the bit
   *
   * @param[in,out] field The bitfield
   * @param[in]     idx   The number of the bit to toggle
   */
  static inline void bf_toggle(uint8_t field[], size_t idx)
  {
      field[idx / 8] ^= (1u << (idx % 8));
  }
  
  /**
   * @brief  Check if the bet is set
   *
   * @param[in,out] field The bitfield
   * @param[in]     idx   The number of the bit to check
   */
  static inline bool bf_isset(uint8_t field[], size_t idx)
  {
      return (field[idx / 8] & (1u << (idx % 8)));
  }
  
  /**
   * @brief  Atomically get the number of an unset bit and set it
   *
   * This function can be used to record e.g., empty entries in an array.
   *
   * @param[in,out] field The bitfield
   * @param[in]     size  The size of the bitfield
   *
   * @return      number of bit that was set
   * @return      -1 if no bit was unset
   */
  int bf_get_unset(uint8_t field[], int size);
  
  #ifdef __cplusplus
  }
  #endif
  
  /** @} */
  #endif /* BITFIELD_H */