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annotate bn_mp_mul.c @ 282:91fbc376f010 libtommath-orig libtommath-0.35

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Import of libtommath 0.35 From ltm-0.35.tar.bz2 SHA1 of 3f193dbae9351e92d02530994fa18236f7fde01c
author Matt Johnston <matt@ucc.asn.au>
date Wed, 08 Mar 2006 13:16:18 +0000
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children 97db060d0ef5
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1 #include <tommath.h>
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2 #ifdef BN_MP_MUL_C
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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 /* high level multiplication (handles sign) */
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19 int mp_mul (mp_int * a, mp_int * b, mp_int * c)
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20 {
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21 int res, neg;
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22 neg = (a->sign == b->sign) ? MP_ZPOS : MP_NEG;
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23
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24 /* use Toom-Cook? */
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25 #ifdef BN_MP_TOOM_MUL_C
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26 if (MIN (a->used, b->used) >= TOOM_MUL_CUTOFF) {
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27 res = mp_toom_mul(a, b, c);
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28 } else
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29 #endif
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30 #ifdef BN_MP_KARATSUBA_MUL_C
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31 /* use Karatsuba? */
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32 if (MIN (a->used, b->used) >= KARATSUBA_MUL_CUTOFF) {
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33 res = mp_karatsuba_mul (a, b, c);
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34 } else
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35 #endif
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36 {
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37 /* can we use the fast multiplier?
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38 *
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39 * The fast multiplier can be used if the output will
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40 * have less than MP_WARRAY digits and the number of
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41 * digits won't affect carry propagation
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42 */
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43 int digs = a->used + b->used + 1;
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44
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45 #ifdef BN_FAST_S_MP_MUL_DIGS_C
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46 if ((digs < MP_WARRAY) &&
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47 MIN(a->used, b->used) <=
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48 (1 << ((CHAR_BIT * sizeof (mp_word)) - (2 * DIGIT_BIT)))) {
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49 res = fast_s_mp_mul_digs (a, b, c, digs);
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50 } else
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51 #endif
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52 #ifdef BN_S_MP_MUL_DIGS_C
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53 res = s_mp_mul (a, b, c); /* uses s_mp_mul_digs */
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54 #else
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55 res = MP_VAL;
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56 #endif
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57
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58 }
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59 c->sign = (c->used > 0) ? neg : MP_ZPOS;
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60 return res;
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61 }
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62 #endif