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 EXPORT_SYMBOL_GPL(mpi_sub); 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); 156