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- /****************************************************************************
- * libs/libc/misc/lib_umul64.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
- * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
- * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
- * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
- * POSSIBILITY OF SUCH DAMAGE.
- *
- ****************************************************************************/
- /****************************************************************************
- * Included Files
- ****************************************************************************/
- #include <nuttx/lib/math32.h>
- /****************************************************************************
- * Public Functions
- ****************************************************************************/
- /****************************************************************************
- * Name: umul64
- *
- * Description:
- * Multiply two 64-bit values, factor1 and factor2, and return the
- * truncated 64-bit product.
- *
- * Input Parameters:
- * factor1 and factor2 - The values to be multiplied
- * product - The location to return the product of the two values.
- *
- ****************************************************************************/
- void umul64(FAR const struct uint64_s *factor1,
- FAR const struct uint64_s *factor2,
- FAR struct uint64_s *product)
- {
- struct uint64_s part1;
- struct uint64_s part2;
- /* factor1 = factor1->ms << 32 + factor1->ls
- * factor2 = factor2->ms << 32 + factor2->ls
- *
- * Full 128-bit product:
- * factor1 * factor2 = (factor1->ms * factor2->ms << 64) +
- * factor1->ls * (factor2->ms << 32) +
- * factor2->ls * (factor1->ms << 32) +
- * factor1->ls * factor2->ls
- *
- * Truncated, 64-bit product:
- * factor1 * factor2 = (factor1->ls * factor2->ms +
- * factor2->ls * factor1->ms) << 32) +
- * factor1->ls * factor2->ls
- *
- * part1 = (factor1->ls * factor2->ms +
- * factor2->ls * factor1->ms) << 32)
- * part2 = factor1->ls * factor2->ls
- * factor1 * factor2 = part1 + part2
- */
- /* Get part1 = factor1->ls * factor2->ms + factor2->ls * factor1->ms,
- * shifting left by 32-bits (truncating to 64-bits)
- */
- part1.ms = factor1->ls * factor2->ms +
- factor2->ls * factor2->ms;
- part1.ls = 0;
- /* Get the full 64-bit part2 = factor1->ls * factor2->ls */
- umul32(factor1->ls, factor2->ls, &part2);
- /* The product is then the sum */
- uadd64(&part1, &part2, product);
- }
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