| 1 | /* |
| 2 | * This file is part of DisOrder. |
| 3 | * Copyright (C) 2005, 2007, 2008 Richard Kettlewell |
| 4 | * |
| 5 | * This program is free software: you can redistribute it and/or modify |
| 6 | * it under the terms of the GNU General Public License as published by |
| 7 | * the Free Software Foundation, either version 3 of the License, or |
| 8 | * (at your option) any later version. |
| 9 | * |
| 10 | * This program is distributed in the hope that it will be useful, |
| 11 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 12 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| 13 | * GNU General Public License for more details. |
| 14 | * |
| 15 | * You should have received a copy of the GNU General Public License |
| 16 | * along with this program. If not, see <http://www.gnu.org/licenses/>. |
| 17 | */ |
| 18 | /** @file lib/basen.c @brief Arbitrary base conversion |
| 19 | * |
| 20 | * The functions in this file handle arbitrary-size non-negative integers, |
| 21 | * represented as a bigendian (MSW first) sequence of @c unsigned @c long |
| 22 | * words. The words themselves use the native byte order. |
| 23 | */ |
| 24 | |
| 25 | #include "common.h" |
| 26 | |
| 27 | #include "basen.h" |
| 28 | |
| 29 | /** @brief Test whether v is 0 |
| 30 | * @param v Pointer to bigendian bignum |
| 31 | * @param nwords Length of bignum |
| 32 | * @return !v |
| 33 | */ |
| 34 | static int zero(const uint32_t *v, int nwords) { |
| 35 | int n; |
| 36 | |
| 37 | for(n = 0; n < nwords && !v[n]; ++n) |
| 38 | ; |
| 39 | return n == nwords; |
| 40 | } |
| 41 | |
| 42 | /** @brief Divide v by m returning the remainder. |
| 43 | * @param v Pointer to bigendian bignum |
| 44 | * @param nwords Length of bignum |
| 45 | * @param m Divisor (must not be 0) |
| 46 | * @return Remainder |
| 47 | * |
| 48 | * The quotient is stored in @p v. |
| 49 | */ |
| 50 | static unsigned divide(uint32_t *v, int nwords, unsigned long m) { |
| 51 | unsigned long r = 0, a, b; |
| 52 | int n; |
| 53 | |
| 54 | /* we do the divide 16 bits at a time */ |
| 55 | for(n = 0; n < nwords; ++n) { |
| 56 | a = v[n] >> 16; |
| 57 | b = v[n] & 0xFFFF; |
| 58 | a += r << 16; |
| 59 | r = a % m; |
| 60 | a /= m; |
| 61 | b += r << 16; |
| 62 | r = b % m; |
| 63 | b /= m; |
| 64 | v[n] = (a << 16) + b; |
| 65 | } |
| 66 | return r; |
| 67 | } |
| 68 | |
| 69 | /** @brief Multiple v by m and add a |
| 70 | * @param v Pointer to bigendian bignum |
| 71 | * @param nwords Length of bignum |
| 72 | * @param m Value to multiply by |
| 73 | * @param a Value to add |
| 74 | * @return 0 on success, non-0 on overflow |
| 75 | * |
| 76 | * Does v = m * v + a. |
| 77 | */ |
| 78 | static int mla(uint32_t *v, int nwords, uint32_t m, uint32_t a) { |
| 79 | int n = nwords - 1; |
| 80 | uint32_t carry = a; |
| 81 | |
| 82 | while(n >= 0) { |
| 83 | const uint64_t p = (uint64_t)v[n] * m + carry; |
| 84 | carry = (uint32_t)(p >> 32); |
| 85 | v[n] = (uint32_t)p; |
| 86 | --n; |
| 87 | } |
| 88 | /* If there is still a carry then we overflowed */ |
| 89 | return !!carry; |
| 90 | } |
| 91 | |
| 92 | static const char basen_chars[] = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"; |
| 93 | |
| 94 | /** @brief Convert v to a chosen base |
| 95 | * @param v Pointer to bigendian bignum (modified!) |
| 96 | * @param nwords Length of bignum |
| 97 | * @param buffer Output buffer |
| 98 | * @param bufsize Size of output buffer |
| 99 | * @param base Number base (2..62) |
| 100 | * @return 0 on success, -1 if the buffer is too small |
| 101 | * |
| 102 | * Converts @p v to a string in the given base using decimal digits, lower case |
| 103 | * letters and upper case letters as digits. |
| 104 | * |
| 105 | * The inverse of nesab(). |
| 106 | */ |
| 107 | int basen(uint32_t *v, |
| 108 | int nwords, |
| 109 | char buffer[], |
| 110 | size_t bufsize, |
| 111 | unsigned base) { |
| 112 | size_t i = bufsize; |
| 113 | |
| 114 | do { |
| 115 | if(i <= 1) |
| 116 | return -1; /* overflow */ |
| 117 | buffer[--i] = basen_chars[divide(v, nwords, base)]; |
| 118 | } while(!zero(v, nwords)); |
| 119 | memmove(buffer, buffer + i, bufsize - i); |
| 120 | buffer[bufsize - i] = 0; |
| 121 | return 0; |
| 122 | } |
| 123 | |
| 124 | /** @brief Convert a string back to a large integer in an arbitrary base |
| 125 | * @param v Where to store result as a bigendian bignum |
| 126 | * @param nwords Space available in @p v |
| 127 | * @param s Input string |
| 128 | * @param base Number base (2..62) |
| 129 | * @return 0 on success, non-0 on overflow or invalid input |
| 130 | * |
| 131 | * The inverse of basen(). If the number is much smaller than the buffer then |
| 132 | * the first words will be 0. |
| 133 | */ |
| 134 | int nesab(uint32_t *v, |
| 135 | int nwords, |
| 136 | const char *s, |
| 137 | unsigned base) { |
| 138 | /* Initialize to 0 */ |
| 139 | memset(v, 0, nwords * sizeof *v); |
| 140 | while(*s) { |
| 141 | const char *dp = strchr(basen_chars, *s++); |
| 142 | if(!dp) |
| 143 | return -1; |
| 144 | if(mla(v, nwords, base, dp - basen_chars)) |
| 145 | return -1; |
| 146 | } |
| 147 | return 0; |
| 148 | } |
| 149 | |
| 150 | /* |
| 151 | Local Variables: |
| 152 | c-basic-offset:2 |
| 153 | comment-column:40 |
| 154 | fill-column:79 |
| 155 | End: |
| 156 | */ |