incubator-nuttx/libc/misc/lib_uadd64.c

/****************************************************************************
 * libc/misc/lib_uadd64.c
 *
 *   Copyright (C) 2016 Gregory Nutt. All rights reserved.
 *   Author: Gregory Nutt <gnutt@nuttx.org>
 *
 * 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.
 * 3. Neither the name NuttX nor the names of its contributors may be
 *    used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "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
 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
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 *
 ****************************************************************************/

/****************************************************************************
 * Included Files
 ****************************************************************************/

#include <nuttx/lib/math32.h>

/****************************************************************************
 * Public Functions
 ****************************************************************************/

/****************************************************************************
 * Name: uadd64
 *
 * Description:
 *   Add two 64-bit values and return a 64-bit sum.
 *
 * Input Parameters:
 *   term1 and term2 - The values to be added
 *   sum - The location to return the product of the two values.  sum may
 *     be one of term1 or term2
 *
 ****************************************************************************/

void uadd64(FAR const struct uint64_s *term1,
            FAR const struct uint64_s *term2,
            FAR struct uint64_s *sum)
{
  /* Get the MS part of the sum */

  sum->ms = term1->ms + term2->ms;

  /* Check for carry, i.e., that is when:
   *
   * term1->ls + term2->ls > UINT32_MAX
   */

  if ((UINT32_MAX - term1->ls) > term2->ls)
    {
      sum->ms++;
    }

  /* Get the LS part of the sum */

  sum->ls = term1->ls + term2->ls;
}