## File: bn_mp_div_2d.c

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libtommath 0.42.0-1
 `12345678910111213141516171819202122232425262728293031323334353637383940414243444546474849505152535455565758596061626364656667686970717273747576777879808182838485868788899091929394959697` ``````#include #ifdef BN_MP_DIV_2D_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@gmail.com, http://libtom.org */ /* shift right by a certain bit count (store quotient in c, optional remainder in d) */ int mp_div_2d (mp_int * a, int b, mp_int * c, mp_int * d) { mp_digit D, r, rr; int x, res; mp_int t; /* if the shift count is <= 0 then we do no work */ if (b <= 0) { res = mp_copy (a, c); if (d != NULL) { mp_zero (d); } return res; } if ((res = mp_init (&t)) != MP_OKAY) { return res; } /* get the remainder */ if (d != NULL) { if ((res = mp_mod_2d (a, b, &t)) != MP_OKAY) { mp_clear (&t); return res; } } /* copy */ if ((res = mp_copy (a, c)) != MP_OKAY) { mp_clear (&t); return res; } /* shift by as many digits in the bit count */ if (b >= (int)DIGIT_BIT) { mp_rshd (c, b / DIGIT_BIT); } /* shift any bit count < DIGIT_BIT */ D = (mp_digit) (b % DIGIT_BIT); if (D != 0) { register mp_digit *tmpc, mask, shift; /* mask */ mask = (((mp_digit)1) << D) - 1; /* shift for lsb */ shift = DIGIT_BIT - D; /* alias */ tmpc = c->dp + (c->used - 1); /* carry */ r = 0; for (x = c->used - 1; x >= 0; x--) { /* get the lower bits of this word in a temp */ rr = *tmpc & mask; /* shift the current word and mix in the carry bits from the previous word */ *tmpc = (*tmpc >> D) | (r << shift); --tmpc; /* set the carry to the carry bits of the current word found above */ r = rr; } } mp_clamp (c); if (d != NULL) { mp_exch (&t, d); } mp_clear (&t); return MP_OKAY; } #endif /* \$Source\$ */ /* \$Revision: 0.41 \$ */ /* \$Date: 2007-04-18 09:58:18 +0000 \$ */ ``````