annotate bn_mp_reduce_2k.c @ 146:81bc23421b45 libtommath

Clean up the merge, remove some unneeded files etc
author Matt Johnston <matt@ucc.asn.au>
date Sun, 19 Dec 2004 16:18:40 +0000
parents d29b64170cf0
children d8254fc979e9
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d29b64170cf0 import of libtommath 0.32
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1 #include <tommath.h>
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2 #ifdef BN_MP_REDUCE_2K_C
2
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3 /* LibTomMath, multiple-precision integer library -- Tom St Denis
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4 *
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5 * LibTomMath is a library that provides multiple-precision
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6 * integer arithmetic as well as number theoretic functionality.
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7 *
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8 * The library was designed directly after the MPI library by
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9 * Michael Fromberger but has been written from scratch with
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10 * additional optimizations in place.
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11 *
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12 * The library is free for all purposes without any express
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13 * guarantee it works.
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14 *
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15 * Tom St Denis, [email protected], http://math.libtomcrypt.org
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16 */
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17
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18 /* reduces a modulo n where n is of the form 2**p - d */
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19 int
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20 mp_reduce_2k(mp_int *a, mp_int *n, mp_digit d)
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21 {
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22 mp_int q;
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23 int p, res;
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24
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25 if ((res = mp_init(&q)) != MP_OKAY) {
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26 return res;
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27 }
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28
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29 p = mp_count_bits(n);
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30 top:
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31 /* q = a/2**p, a = a mod 2**p */
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32 if ((res = mp_div_2d(a, p, &q, a)) != MP_OKAY) {
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33 goto ERR;
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34 }
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35
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36 if (d != 1) {
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37 /* q = q * d */
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38 if ((res = mp_mul_d(&q, d, &q)) != MP_OKAY) {
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39 goto ERR;
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40 }
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41 }
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42
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43 /* a = a + q */
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44 if ((res = s_mp_add(a, &q, a)) != MP_OKAY) {
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45 goto ERR;
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46 }
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47
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48 if (mp_cmp_mag(a, n) != MP_LT) {
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49 s_mp_sub(a, n, a);
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50 goto top;
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51 }
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52
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53 ERR:
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54 mp_clear(&q);
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55 return res;
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56 }
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57
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d29b64170cf0 import of libtommath 0.32
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58 #endif