generic_mpih-mul1.c 1.3 KB

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  1. // SPDX-License-Identifier: GPL-2.0-or-later
  2. /* mpihelp-mul_1.c - MPI helper functions
  3. * Copyright (C) 1994, 1996, 1997, 1998, 2001 Free Software Foundation, Inc.
  4. *
  5. * This file is part of GnuPG.
  6. *
  7. * Note: This code is heavily based on the GNU MP Library.
  8. * Actually it's the same code with only minor changes in the
  9. * way the data is stored; this is to support the abstraction
  10. * of an optional secure memory allocation which may be used
  11. * to avoid revealing of sensitive data due to paging etc.
  12. * The GNU MP Library itself is published under the LGPL;
  13. * however I decided to publish this code under the plain GPL.
  14. */
  15. #include "mpi-internal.h"
  16. #include "longlong.h"
  17. mpi_limb_t
  18. mpihelp_mul_1(mpi_ptr_t res_ptr, mpi_ptr_t s1_ptr, mpi_size_t s1_size,
  19. mpi_limb_t s2_limb)
  20. {
  21. mpi_limb_t cy_limb;
  22. mpi_size_t j;
  23. mpi_limb_t prod_high, prod_low;
  24. /* The loop counter and index J goes from -S1_SIZE to -1. This way
  25. * the loop becomes faster. */
  26. j = -s1_size;
  27. /* Offset the base pointers to compensate for the negative indices. */
  28. s1_ptr -= j;
  29. res_ptr -= j;
  30. cy_limb = 0;
  31. do {
  32. umul_ppmm(prod_high, prod_low, s1_ptr[j], s2_limb);
  33. prod_low += cy_limb;
  34. cy_limb = (prod_low < cy_limb ? 1 : 0) + prod_high;
  35. res_ptr[j] = prod_low;
  36. } while (++j);
  37. return cy_limb;
  38. }