# public libtom /libtommath

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 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 `#include #ifdef BN_MP_REDUCE_C/* LibTomMath, multiple-precision integer library -- Tom St Denis * * LibTomMath is a library that provides multiple-precision * integer arithmetic as well as number theoretic functionality. * * The library was designed directly after the MPI library by * Michael Fromberger but has been written from scratch with * additional optimizations in place. * * The library is free for all purposes without any express * guarantee it works. * * Tom St Denis, tomstdenis@iahu.ca, http://math.libtomcrypt.org *//* reduces x mod m, assumes 0 < x < m**2, mu is * precomputed via mp_reduce_setup. * From HAC pp.604 Algorithm 14.42 */intmp_reduce (mp_int * x, mp_int * m, mp_int * mu){  mp_int q;  int res, um = m->used;  /* q = x */  if ((res = mp_init_copy (&q, x)) != MP_OKAY) {    return res;  }  /* q1 = x / b**(k-1) */  mp_rshd (&q, um - 1);   /* according to HAC this optimization is ok */  if (((unsigned long) um) > (((mp_digit)1) << (DIGIT_BIT - 1))) {    if ((res = mp_mul (&q, mu, &q)) != MP_OKAY) {      goto CLEANUP;    }  } else {#ifdef BN_S_MP_MUL_HIGH_DIGS_C    if ((res = s_mp_mul_high_digs (&q, mu, &q, um - 1)) != MP_OKAY) {      goto CLEANUP;    }#elif defined(BN_FAST_S_MP_MUL_HIGH_DIGS_C)    if ((res = fast_s_mp_mul_high_digs (&q, mu, &q, um - 1)) != MP_OKAY) {      goto CLEANUP;    }#else     {       res = MP_VAL;      goto CLEANUP;    }#endif  }  /* q3 = q2 / b**(k+1) */  mp_rshd (&q, um + 1);   /* x = x mod b**(k+1), quick (no division) */  if ((res = mp_mod_2d (x, DIGIT_BIT * (um + 1), x)) != MP_OKAY) {    goto CLEANUP;  }  /* q = q * m mod b**(k+1), quick (no division) */  if ((res = s_mp_mul_digs (&q, m, &q, um + 1)) != MP_OKAY) {    goto CLEANUP;  }  /* x = x - q */  if ((res = mp_sub (x, &q, x)) != MP_OKAY) {    goto CLEANUP;  }  /* If x < 0, add b**(k+1) to it */  if (mp_cmp_d (x, 0) == MP_LT) {    mp_set (&q, 1);    if ((res = mp_lshd (&q, um + 1)) != MP_OKAY)      goto CLEANUP;    if ((res = mp_add (x, &q, x)) != MP_OKAY)      goto CLEANUP;  }  /* Back off if it's too big */  while (mp_cmp (x, m) != MP_LT) {    if ((res = s_mp_sub (x, m, x)) != MP_OKAY) {      goto CLEANUP;    }  }  CLEANUP:  mp_clear (&q);  return res;}#endif`
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