File: bn_mp_mod_2d.c

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libtommath 0.42.0-1
 `12345678910111213141516171819202122232425262728293031323334353637383940414243444546474849505152535455` ``````#include #ifdef BN_MP_MOD_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 */ /* calc a value mod 2**b */ int mp_mod_2d (mp_int * a, int b, mp_int * c) { int x, res; /* if b is <= 0 then zero the int */ if (b <= 0) { mp_zero (c); return MP_OKAY; } /* if the modulus is larger than the value than return */ if (b >= (int) (a->used * DIGIT_BIT)) { res = mp_copy (a, c); return res; } /* copy */ if ((res = mp_copy (a, c)) != MP_OKAY) { return res; } /* zero digits above the last digit of the modulus */ for (x = (b / DIGIT_BIT) + ((b % DIGIT_BIT) == 0 ? 0 : 1); x < c->used; x++) { c->dp[x] = 0; } /* clear the digit that is not completely outside/inside the modulus */ c->dp[b / DIGIT_BIT] &= (mp_digit) ((((mp_digit) 1) << (((mp_digit) b) % DIGIT_BIT)) - ((mp_digit) 1)); mp_clamp (c); return MP_OKAY; } #endif /* \$Source\$ */ /* \$Revision: 0.41 \$ */ /* \$Date: 2007-04-18 09:58:18 +0000 \$ */ ``````