generic_mpih-mul3.c 1.3 KB

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748
  1. // SPDX-License-Identifier: GPL-2.0-or-later
  2. /* mpihelp-mul_3.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_submul_1(mpi_ptr_t res_ptr, mpi_ptr_t s1_ptr,
  19. mpi_size_t s1_size, 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. mpi_limb_t x;
  25. /* The loop counter and index J goes from -SIZE to -1. This way
  26. * the loop becomes faster. */
  27. j = -s1_size;
  28. res_ptr -= j;
  29. s1_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. x = res_ptr[j];
  36. prod_low = x - prod_low;
  37. cy_limb += prod_low > x ? 1 : 0;
  38. res_ptr[j] = prod_low;
  39. } while (++j);
  40. return cy_limb;
  41. }