# rubinius/rubinius

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 #include #ifdef BN_MP_DIV_3_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 */ /* divide by three (based on routine from MPI and the GMP manual) */ int mp_div_3 MPA(mp_int * a, mp_int *c, mp_digit * d) { mp_int q; mp_word w, t; mp_digit b; int res, ix; /* b = 2**DIGIT_BIT / 3 */ b = (((mp_word)1) << ((mp_word)DIGIT_BIT)) / ((mp_word)3); if ((res = mp_init_size(&q, a->used)) != MP_OKAY) { return res; } q.used = a->used; q.sign = a->sign; w = 0; for (ix = a->used - 1; ix >= 0; ix--) { w = (w << ((mp_word)DIGIT_BIT)) | ((mp_word)a->dp[ix]); if (w >= 3) { /* multiply w by [1/3] */ t = (w * ((mp_word)b)) >> ((mp_word)DIGIT_BIT); /* now subtract 3 * [w/3] from w, to get the remainder */ w -= t+t+t; /* fixup the remainder as required since * the optimization is not exact. */ while (w >= 3) { t += 1; w -= 3; } } else { t = 0; } q.dp[ix] = (mp_digit)t; } /* [optional] store the remainder */ if (d != NULL) { *d = (mp_digit)w; } /* [optional] store the quotient */ if (c != NULL) { mp_clamp(&q); mp_managed_copy (MPST, &q, c); } mp_clear(&q); return res; } #endif /* \$Source: /cvs/libtom/libtommath/bn_mp_div_3.c,v \$ */ /* \$Revision: 1.4 \$ */ /* \$Date: 2006/12/28 01:25:13 \$ */
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