LXR linux/lib/mpi/mpi-add.c

   1/* mpi-add.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/****************
  17 * Add the unsigned integer V to the mpi-integer U and store the
  18 * result in W. U and V may be the same.
  19 */
  20void mpi_add_ui(MPI w, MPI u, unsigned long v)
  21{
  22        mpi_ptr_t wp, up;
  23        mpi_size_t usize, wsize;
  24        int usign, wsign;
  25
  26        usize = u->nlimbs;
  27        usign = u->sign;
  28        wsign = 0;
  29
  30        /* If not space for W (and possible carry), increase space.  */
  31        wsize = usize + 1;
  32        if (w->alloced < wsize)
  33                mpi_resize(w, wsize);
  34
  35        /* These must be after realloc (U may be the same as W).  */
  36        up = u->d;
  37        wp = w->d;
  38
  39        if (!usize) {  /* simple */
  40                wp[0] = v;
  41                wsize = v ? 1:0;
  42        } else if (!usign) {  /* mpi is not negative */
  43                mpi_limb_t cy;
  44                cy = mpihelp_add_1(wp, up, usize, v);
  45                wp[usize] = cy;
  46                wsize = usize + cy;
  47        } else {
  48                /* The signs are different.  Need exact comparison to determine
  49                 * which operand to subtract from which.
  50                 */
  51                if (usize == 1 && up[0] < v) {
  52                        wp[0] = v - up[0];
  53                        wsize = 1;
  54                } else {
  55                        mpihelp_sub_1(wp, up, usize, v);
  56                        /* Size can decrease with at most one limb. */
  57                        wsize = usize - (wp[usize-1] == 0);
  58                        wsign = 1;
  59                }
  60        }
  61
  62        w->nlimbs = wsize;
  63        w->sign   = wsign;
  64}
  65
  66
  67void mpi_add(MPI w, MPI u, MPI v)
  68{
  69        mpi_ptr_t wp, up, vp;
  70        mpi_size_t usize, vsize, wsize;
  71        int usign, vsign, wsign;
  72
  73        if (u->nlimbs < v->nlimbs) { /* Swap U and V. */
  74                usize = v->nlimbs;
  75                usign = v->sign;
  76                vsize = u->nlimbs;
  77                vsign = u->sign;
  78                wsize = usize + 1;
  79                RESIZE_IF_NEEDED(w, wsize);
  80                /* These must be after realloc (u or v may be the same as w).  */
  81                up = v->d;
  82                vp = u->d;
  83        } else {
  84                usize = u->nlimbs;
  85                usign = u->sign;
  86                vsize = v->nlimbs;
  87                vsign = v->sign;
  88                wsize = usize + 1;
  89                RESIZE_IF_NEEDED(w, wsize);
  90                /* These must be after realloc (u or v may be the same as w).  */
  91                up = u->d;
  92                vp = v->d;
  93        }
  94        wp = w->d;
  95        wsign = 0;
  96
  97        if (!vsize) {  /* simple */
  98                MPN_COPY(wp, up, usize);
  99                wsize = usize;
 100                wsign = usign;
 101        } else if (usign != vsign) { /* different sign */
 102                /* This test is right since USIZE >= VSIZE */
 103                if (usize != vsize) {
 104                        mpihelp_sub(wp, up, usize, vp, vsize);
 105                        wsize = usize;
 106                        MPN_NORMALIZE(wp, wsize);
 107                        wsign = usign;
 108                } else if (mpihelp_cmp(up, vp, usize) < 0) {
 109                        mpihelp_sub_n(wp, vp, up, usize);
 110                        wsize = usize;
 111                        MPN_NORMALIZE(wp, wsize);
 112                        if (!usign)
 113                                wsign = 1;
 114                } else {
 115                        mpihelp_sub_n(wp, up, vp, usize);
 116                        wsize = usize;
 117                        MPN_NORMALIZE(wp, wsize);
 118                        if (usign)
 119                                wsign = 1;
 120                }
 121        } else { /* U and V have same sign. Add them. */
 122                mpi_limb_t cy = mpihelp_add(wp, up, usize, vp, vsize);
 123                wp[usize] = cy;
 124                wsize = usize + cy;
 125                if (usign)
 126                        wsign = 1;
 127        }
 128
 129        w->nlimbs = wsize;
 130        w->sign = wsign;
 131}
 132EXPORT_SYMBOL_GPL(mpi_add);
 133
 134void mpi_sub(MPI w, MPI u, MPI v)
 135{
 136        MPI vv = mpi_copy(v);
 137        vv->sign = !vv->sign;
 138        mpi_add(w, u, vv);
 139        mpi_free(vv);
 140}
 141
 142
 143void mpi_addm(MPI w, MPI u, MPI v, MPI m)
 144{
 145        mpi_add(w, u, v);
 146        mpi_mod(w, w, m);
 147}
 148EXPORT_SYMBOL_GPL(mpi_addm);
 149
 150void mpi_subm(MPI w, MPI u, MPI v, MPI m)
 151{
 152        mpi_sub(w, u, v);
 153        mpi_mod(w, w, m);
 154}
 155EXPORT_SYMBOL_GPL(mpi_subm);
 156