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 int mpi_add(MPI w, MPI u, MPI v) 17 { 18 mpi_ptr_t wp, up, vp; 19 mpi_size_t usize, vsize, wsize; 20 int usign, vsign, wsign; 21 int err; 22 23 if (u->nlimbs < v->nlimbs) { /* Swap U and V. */ 24 usize = v->nlimbs; 25 usign = v->sign; 26 vsize = u->nlimbs; 27 vsign = u->sign; 28 wsize = usize + 1; 29 err = RESIZE_IF_NEEDED(w, wsize); 30 if (err) 31 return err; 32 /* These must be after realloc (u or v may be the same as w). */ 33 up = v->d; 34 vp = u->d; 35 } else { 36 usize = u->nlimbs; 37 usign = u->sign; 38 vsize = v->nlimbs; 39 vsign = v->sign; 40 wsize = usize + 1; 41 err = RESIZE_IF_NEEDED(w, wsize); 42 if (err) 43 return err; 44 /* These must be after realloc (u or v may be the same as w). */ 45 up = u->d; 46 vp = v->d; 47 } 48 wp = w->d; 49 wsign = 0; 50 51 if (!vsize) { /* simple */ 52 MPN_COPY(wp, up, usize); 53 wsize = usize; 54 wsign = usign; 55 } else if (usign != vsign) { /* different sign */ 56 /* This test is right since USIZE >= VSIZE */ 57 if (usize != vsize) { 58 mpihelp_sub(wp, up, usize, vp, vsize); 59 wsize = usize; 60 MPN_NORMALIZE(wp, wsize); 61 wsign = usign; 62 } else if (mpihelp_cmp(up, vp, usize) < 0) { 63 mpihelp_sub_n(wp, vp, up, usize); 64 wsize = usize; 65 MPN_NORMALIZE(wp, wsize); 66 if (!usign) 67 wsign = 1; 68 } else { 69 mpihelp_sub_n(wp, up, vp, usize); 70 wsize = usize; 71 MPN_NORMALIZE(wp, wsize); 72 if (usign) 73 wsign = 1; 74 } 75 } else { /* U and V have same sign. Add them. */ 76 mpi_limb_t cy = mpihelp_add(wp, up, usize, vp, vsize); 77 wp[usize] = cy; 78 wsize = usize + cy; 79 if (usign) 80 wsign = 1; 81 } 82 83 w->nlimbs = wsize; 84 w->sign = wsign; 85 return 0; 86 } 87 EXPORT_SYMBOL_GPL(mpi_add); 88 89 int mpi_sub(MPI w, MPI u, MPI v) 90 { 91 int err; 92 MPI vv; 93 94 vv = mpi_copy(v); 95 if (!vv) 96 return -ENOMEM; 97 98 vv->sign = !vv->sign; 99 err = mpi_add(w, u, vv); 100 mpi_free(vv); 101 102 return err; 103 } 104 EXPORT_SYMBOL_GPL(mpi_sub); 105 106 int mpi_addm(MPI w, MPI u, MPI v, MPI m) 107 { 108 return mpi_add(w, u, v) ?: 109 mpi_mod(w, w, m); 110 } 111 EXPORT_SYMBOL_GPL(mpi_addm); 112 113 int mpi_subm(MPI w, MPI u, MPI v, MPI m) 114 { 115 return mpi_sub(w, u, v) ?: 116 mpi_mod(w, w, m); 117 } 118 EXPORT_SYMBOL_GPL(mpi_subm); 119