lib/mpi/mpi-mul.c

   1 /* mpi-mul.c  -  MPI functions
   2  * Copyright (C) 1994, 1996, 1998, 2001, 2002,
   3  *               2003 Free Software Foundation, Inc.
   4  *
   5  * This file is part of Libgcrypt.
   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  */
  13
  14 #include "mpi-internal.h"
  15
  16 void mpi_mul(MPI w, MPI u, MPI v)
  17 {
  18         mpi_size_t usize, vsize, wsize;
  19         mpi_ptr_t up, vp, wp;
  20         mpi_limb_t cy;
  21         int usign, vsign, sign_product;
  22         int assign_wp = 0;
  23         mpi_ptr_t tmp_limb = NULL;
  24
  25         if (u->nlimbs < v->nlimbs) {
  26                 /* Swap U and V. */
  27                 usize = v->nlimbs;
  28                 usign = v->sign;
  29                 up    = v->d;
  30                 vsize = u->nlimbs;
  31                 vsign = u->sign;
  32                 vp    = u->d;
  33         } else {
  34                 usize = u->nlimbs;
  35                 usign = u->sign;
  36                 up    = u->d;
  37                 vsize = v->nlimbs;
  38                 vsign = v->sign;
  39                 vp    = v->d;
  40         }
  41         sign_product = usign ^ vsign;
  42         wp = w->d;
  43
  44         /* Ensure W has space enough to store the result.  */
  45         wsize = usize + vsize;
  46         if (w->alloced < wsize) {
  47                 if (wp == up || wp == vp) {
  48                         wp = mpi_alloc_limb_space(wsize);
  49                         assign_wp = 1;
  50                 } else {
  51                         mpi_resize(w, wsize);
  52                         wp = w->d;
  53                 }
  54         } else { /* Make U and V not overlap with W.    */
  55                 if (wp == up) {
  56                         /* W and U are identical.  Allocate temporary space for U. */
  57                         up = tmp_limb = mpi_alloc_limb_space(usize);
  58                         /* Is V identical too?  Keep it identical with U.  */
  59                         if (wp == vp)
  60                                 vp = up;
  61                         /* Copy to the temporary space.  */
  62                         MPN_COPY(up, wp, usize);
  63                 } else if (wp == vp) {
  64                         /* W and V are identical.  Allocate temporary space for V. */
  65                         vp = tmp_limb = mpi_alloc_limb_space(vsize);
  66                         /* Copy to the temporary space.  */
  67                         MPN_COPY(vp, wp, vsize);
  68                 }
  69         }
  70
  71         if (!vsize)
  72                 wsize = 0;
  73         else {
  74                 mpihelp_mul(wp, up, usize, vp, vsize, &cy);
  75                 wsize -= cy ? 0:1;
  76         }
  77
  78         if (assign_wp)
  79                 mpi_assign_limb_space(w, wp, wsize);
  80         w->nlimbs = wsize;
  81         w->sign = sign_product;
  82         if (tmp_limb)
  83                 mpi_free_limb_space(tmp_limb);
  84 }
  85
  86 void mpi_mulm(MPI w, MPI u, MPI v, MPI m)
  87 {
  88         mpi_mul(w, u, v);
  89         mpi_tdiv_r(w, w, m);
  90 }
  91 EXPORT_SYMBOL_GPL(mpi_mulm);