nuttx/libs/libc/misc/lib_usub64.c

/****************************************************************************
 * libs/libc/misc/lib_usub64.c
 *
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.  The
 * ASF licenses this file to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance with the
 * License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
 * License for the specific language governing permissions and limitations
 * under the License.
 *
 ****************************************************************************/

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

#include <nuttx/lib/math32.h>

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

/****************************************************************************
 * Name: usub64
 *
 * Description:
 *   Subtract two 64-bit values 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 usub64(FAR const struct uint64_s *minuend,
            FAR const struct uint64_s *subtrahend,
            FAR struct uint64_s *difference)
{
  /* Get the MS part of the difference */

  difference->ms = minuend->ms - subtrahend->ms;

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

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

  /* Get the LS part of the difference */

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