| 1 | #include <tommath.h> |
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| 2 | #ifdef BN_MP_DIV_2D_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 | /* shift right by a certain bit count (store quotient in c, optional remainder in d) */ |
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| 19 | int mp_div_2d (mp_int * a, int b, mp_int * c, mp_int * d) |
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| 20 | { |
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| 21 | mp_digit D, r, rr; |
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| 22 | int x, res; |
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| 23 | mp_int t; |
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| 24 | |
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| 25 | |
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| 26 | /* if the shift count is <= 0 then we do no work */ |
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| 27 | if (b <= 0) { |
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| 28 | res = mp_copy (a, c); |
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| 29 | if (d != NULL) { |
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| 30 | mp_zero (d); |
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| 31 | } |
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| 32 | return res; |
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| 33 | } |
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| 34 | |
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| 35 | if ((res = mp_init (&t)) != MP_OKAY) { |
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| 36 | return res; |
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| 37 | } |
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| 38 | |
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| 39 | /* get the remainder */ |
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| 40 | if (d != NULL) { |
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| 41 | if ((res = mp_mod_2d (a, b, &t)) != MP_OKAY) { |
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| 42 | mp_clear (&t); |
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| 43 | return res; |
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| 44 | } |
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| 45 | } |
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| 46 | |
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| 47 | /* copy */ |
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| 48 | if ((res = mp_copy (a, c)) != MP_OKAY) { |
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| 49 | mp_clear (&t); |
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| 50 | return res; |
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| 51 | } |
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| 52 | |
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| 53 | /* shift by as many digits in the bit count */ |
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| 54 | if (b >= (int)DIGIT_BIT) { |
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| 55 | mp_rshd (c, b / DIGIT_BIT); |
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| 56 | } |
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| 57 | |
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| 58 | /* shift any bit count < DIGIT_BIT */ |
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| 59 | D = (mp_digit) (b % DIGIT_BIT); |
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| 60 | if (D != 0) { |
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| 61 | register mp_digit *tmpc, mask, shift; |
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| 62 | |
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| 63 | /* mask */ |
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| 64 | mask = (((mp_digit)1) << D) - 1; |
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| 65 | |
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| 66 | /* shift for lsb */ |
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| 67 | shift = DIGIT_BIT - D; |
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| 68 | |
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| 69 | /* alias */ |
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| 70 | tmpc = c->dp + (c->used - 1); |
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| 71 | |
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| 72 | /* carry */ |
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| 73 | r = 0; |
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| 74 | for (x = c->used - 1; x >= 0; x--) { |
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| 75 | /* get the lower bits of this word in a temp */ |
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| 76 | rr = *tmpc & mask; |
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| 77 | |
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| 78 | /* shift the current word and mix in the carry bits from the previous word */ |
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| 79 | *tmpc = (*tmpc >> D) | (r << shift); |
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| 80 | --tmpc; |
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| 81 | |
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| 82 | /* set the carry to the carry bits of the current word found above */ |
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| 83 | r = rr; |
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| 84 | } |
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| 85 | } |
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| 86 | mp_clamp (c); |
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| 87 | if (d != NULL) { |
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| 88 | mp_exch (&t, d); |
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| 89 | } |
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| 90 | mp_clear (&t); |
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| 91 | return MP_OKAY; |
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| 92 | } |
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| 93 | #endif |
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| 94 | |
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| 95 | /* $Source: /cvsroot/tcl/libtommath/bn_mp_div_2d.c,v $ */ |
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| 96 | /* $Revision: 1.1.1.3 $ */ |
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| 97 | /* $Date: 2006/12/01 00:08:11 $ */ |
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