| 1 | #include <tommath.h> |
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| 2 | #ifdef BN_MP_MUL_2_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, tomstdenis@gmail.com, http://math.libtomcrypt.com |
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| 16 | */ |
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| 17 | |
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| 18 | /* b = a*2 */ |
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| 19 | int mp_mul_2(mp_int * a, mp_int * b) |
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| 20 | { |
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| 21 | int x, res, oldused; |
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| 22 | |
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| 23 | /* grow to accomodate result */ |
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| 24 | if (b->alloc < a->used + 1) { |
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| 25 | if ((res = mp_grow (b, a->used + 1)) != MP_OKAY) { |
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| 26 | return res; |
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| 27 | } |
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| 28 | } |
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| 29 | |
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| 30 | oldused = b->used; |
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| 31 | b->used = a->used; |
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| 32 | |
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| 33 | { |
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| 34 | register mp_digit r, rr, *tmpa, *tmpb; |
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| 35 | |
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| 36 | /* alias for source */ |
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| 37 | tmpa = a->dp; |
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| 38 | |
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| 39 | /* alias for dest */ |
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| 40 | tmpb = b->dp; |
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| 41 | |
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| 42 | /* carry */ |
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| 43 | r = 0; |
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| 44 | for (x = 0; x < a->used; x++) { |
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| 45 | |
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| 46 | /* get what will be the *next* carry bit from the |
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| 47 | * MSB of the current digit |
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| 48 | */ |
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| 49 | rr = *tmpa >> ((mp_digit)(DIGIT_BIT - 1)); |
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| 50 | |
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| 51 | /* now shift up this digit, add in the carry [from the previous] */ |
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| 52 | *tmpb++ = ((*tmpa++ << ((mp_digit)1)) | r) & MP_MASK; |
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| 53 | |
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| 54 | /* copy the carry that would be from the source |
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| 55 | * digit into the next iteration |
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| 56 | */ |
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| 57 | r = rr; |
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| 58 | } |
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| 59 | |
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| 60 | /* new leading digit? */ |
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| 61 | if (r != 0) { |
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| 62 | /* add a MSB which is always 1 at this point */ |
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| 63 | *tmpb = 1; |
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| 64 | ++(b->used); |
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| 65 | } |
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| 66 | |
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| 67 | /* now zero any excess digits on the destination |
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| 68 | * that we didn't write to |
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| 69 | */ |
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| 70 | tmpb = b->dp + b->used; |
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| 71 | for (x = b->used; x < oldused; x++) { |
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| 72 | *tmpb++ = 0; |
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| 73 | } |
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| 74 | } |
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| 75 | b->sign = a->sign; |
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| 76 | return MP_OKAY; |
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| 77 | } |
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| 78 | #endif |
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| 79 | |
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| 80 | /* $Source: /cvsroot/tcl/libtommath/bn_mp_mul_2.c,v $ */ |
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| 81 | /* $Revision: 1.1.1.3 $ */ |
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| 82 | /* $Date: 2006/12/01 00:08:11 $ */ |
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