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  */
  20 void 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
  67 void 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 }
 132 EXPORT_SYMBOL_GPL(mpi_add);
 133
 134 void 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
 143 void mpi_addm(MPI w, MPI u, MPI v, MPI m)
 144 {
 145         mpi_add(w, u, v);
 146         mpi_mod(w, w, m);
 147 }
 148 EXPORT_SYMBOL_GPL(mpi_addm);
 149
 150 void mpi_subm(MPI w, MPI u, MPI v, MPI m)
 151 {
 152         mpi_sub(w, u, v);
 153         mpi_mod(w, w, m);
 154 }
 155 EXPORT_SYMBOL_GPL(mpi_subm);