C++ (Cpp) uadd64 Examples

Example #1

File: lib_umul32x64.c Project: hll4fork/NuttX

void umul32x64(uint32_t factor1, FAR const struct uint64_s *factor2,
              FAR struct uint64_s *product)
{
  struct uint64_s part1;
  struct uint64_s part2;

  /* factor2 = factor2->ms << 32 + factor2->ls
   *
   * Full 128-bit product:
   *   factor1 * factor2 = factor1 * (factor2->ms << 32) +
   *                       factor1 * factor2->ls
   */

  /* Get part1 = factor1 * factor2->ms, shifting left by 32-bits
   * (truncating to 64-bits)
   */

  part1.ms = factor1 * factor2->ms;
  part1.ls = 0;

  /* Get the full 64-bit part2 = factor1 * factor2->ls */

  umul32(factor1, factor2->ls, &part2);

  /* The product is then the sum */

  uadd64(&part1, &part2, product);
}

Example #2

File: lib_umul64.c Project: acassis/ros2_nuttx

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);
}