generic_mpih-add1.c 1.3 KB

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  1. // SPDX-License-Identifier: GPL-2.0-or-later
  2. /* mpihelp-add_1.c - MPI helper functions
  3. * Copyright (C) 1994, 1996, 1997, 1998,
  4. * 2000 Free Software Foundation, Inc.
  5. *
  6. * This file is part of GnuPG.
  7. *
  8. * Note: This code is heavily based on the GNU MP Library.
  9. * Actually it's the same code with only minor changes in the
  10. * way the data is stored; this is to support the abstraction
  11. * of an optional secure memory allocation which may be used
  12. * to avoid revealing of sensitive data due to paging etc.
  13. * The GNU MP Library itself is published under the LGPL;
  14. * however I decided to publish this code under the plain GPL.
  15. */
  16. #include "mpi-internal.h"
  17. #include "longlong.h"
  18. mpi_limb_t
  19. mpihelp_add_n(mpi_ptr_t res_ptr, mpi_ptr_t s1_ptr,
  20. mpi_ptr_t s2_ptr, mpi_size_t size)
  21. {
  22. mpi_limb_t x, y, cy;
  23. mpi_size_t j;
  24. /* The loop counter and index J goes from -SIZE to -1. This way
  25. the loop becomes faster. */
  26. j = -size;
  27. /* Offset the base pointers to compensate for the negative indices. */
  28. s1_ptr -= j;
  29. s2_ptr -= j;
  30. res_ptr -= j;
  31. cy = 0;
  32. do {
  33. y = s2_ptr[j];
  34. x = s1_ptr[j];
  35. y += cy; /* add previous carry to one addend */
  36. cy = y < cy; /* get out carry from that addition */
  37. y += x; /* add other addend */
  38. cy += y < x; /* get out carry from that add, combine */
  39. res_ptr[j] = y;
  40. } while (++j);
  41. return cy;
  42. }