| [25] | 1 | #include <tommath.h> |
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| 2 | #ifdef BN_MP_DIV_D_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 | static int s_is_power_of_two(mp_digit b, int *p) |
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| 19 | { |
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| 20 | int x; |
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| 21 | |
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| 22 | /* quick out - if (b & (b-1)) isn't zero, b isn't a power of two */ |
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| 23 | if ((b & (b-1)) != 0) { |
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| 24 | return 0; |
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| 25 | } |
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| 26 | for (x = 1; x < DIGIT_BIT; x++) { |
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| 27 | if (b == (((mp_digit)1)<<x)) { |
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| 28 | *p = x; |
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| 29 | return 1; |
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| 30 | } |
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| 31 | } |
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| 32 | return 0; |
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| 33 | } |
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| 34 | |
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| 35 | /* single digit division (based on routine from MPI) */ |
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| 36 | int mp_div_d (mp_int * a, mp_digit b, mp_int * c, mp_digit * d) |
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| 37 | { |
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| 38 | mp_int q; |
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| 39 | mp_word w; |
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| 40 | mp_digit t; |
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| 41 | int res, ix; |
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| 42 | |
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| 43 | /* cannot divide by zero */ |
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| 44 | if (b == 0) { |
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| 45 | return MP_VAL; |
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| 46 | } |
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| 47 | |
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| 48 | /* quick outs */ |
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| 49 | if (b == 1 || mp_iszero(a) == 1) { |
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| 50 | if (d != NULL) { |
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| 51 | *d = 0; |
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| 52 | } |
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| 53 | if (c != NULL) { |
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| 54 | return mp_copy(a, c); |
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| 55 | } |
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| 56 | return MP_OKAY; |
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| 57 | } |
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| 58 | |
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| 59 | /* power of two ? */ |
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| 60 | if (s_is_power_of_two(b, &ix) == 1) { |
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| 61 | if (d != NULL) { |
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| 62 | *d = a->dp[0] & ((((mp_digit)1)<<ix) - 1); |
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| 63 | } |
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| 64 | if (c != NULL) { |
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| 65 | return mp_div_2d(a, ix, c, NULL); |
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| 66 | } |
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| 67 | return MP_OKAY; |
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| 68 | } |
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| 69 | |
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| 70 | #ifdef BN_MP_DIV_3_C |
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| 71 | /* three? */ |
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| 72 | if (b == 3) { |
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| 73 | return mp_div_3(a, c, d); |
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| 74 | } |
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| 75 | #endif |
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| 76 | |
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| 77 | /* no easy answer [c'est la vie]. Just division */ |
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| 78 | if ((res = mp_init_size(&q, a->used)) != MP_OKAY) { |
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| 79 | return res; |
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| 80 | } |
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| 81 | |
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| 82 | q.used = a->used; |
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| 83 | q.sign = a->sign; |
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| 84 | w = 0; |
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| 85 | for (ix = a->used - 1; ix >= 0; ix--) { |
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| 86 | w = (w << ((mp_word)DIGIT_BIT)) | ((mp_word)a->dp[ix]); |
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| 87 | |
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| 88 | if (w >= b) { |
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| 89 | t = (mp_digit)(w / b); |
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| 90 | w -= ((mp_word)t) * ((mp_word)b); |
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| 91 | } else { |
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| 92 | t = 0; |
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| 93 | } |
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| 94 | q.dp[ix] = (mp_digit)t; |
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| 95 | } |
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| 96 | |
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| 97 | if (d != NULL) { |
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| 98 | *d = (mp_digit)w; |
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| 99 | } |
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| 100 | |
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| 101 | if (c != NULL) { |
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| 102 | mp_clamp(&q); |
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| 103 | mp_exch(&q, c); |
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| 104 | } |
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| 105 | mp_clear(&q); |
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| 106 | |
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| 107 | return res; |
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| 108 | } |
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| 109 | |
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| 110 | #endif |
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| 111 | |
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| 112 | /* $Source: /cvsroot/tcl/libtommath/bn_mp_div_d.c,v $ */ |
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| 113 | /* $Revision: 1.3 $ */ |
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| 114 | /* $Date: 2006/12/01 05:47:47 $ */ |
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