nuttx/libs/libc/misc/lib_usub64x32.c

/****************************************************************************
 * libs/libc/misc/lib_usub64x32.c
 *
 *   Copyright (C) 2016 Gregory Nutt. All rights reserved.
 *   Author: Gregory Nutt <gnutt@nuttx.org>
 *
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 * modification, are permitted provided that the following conditions
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 *
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 * 2. Redistributions in binary form must reproduce the above copyright
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 *    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
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 ****************************************************************************/

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

#include <nuttx/lib/math32.h>

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

/****************************************************************************
 * Name: usub64x32
 *
 * Description:
 *   Subtract a 32-bit value from a 64-bit value and return the 64-bit
 *   difference.
 *
 * Input Parameters:
 *   minuend    - The number from which another number (the Subtrahend) is
 *     to be subtracted.
 *   subtrahend - The number that is to be subtracted.
 *   difference - The location to return the difference of the two values.
 *     difference may the same as one of minuend or subtrahend.
 *
 ****************************************************************************/

void usub64x32(FAR const struct uint64_s *minuend, uint32_t subtrahend,
               FAR struct uint64_s *difference)
{
  /* Get the MS part of the difference */

  difference->ms = minuend->ms;

  /* Check for a borrow, i.e., that is when:
   *
   * subtrahend->ls > minuend->ls
   */

  if (subtrahend > minuend->ls)
    {
      difference->ms--;
    }

  /* Get the LS part of the difference */

  difference->ls = minuend->ls - subtrahend;
}