1 /* mpq_mul_2exp, mpq_div_2exp - multiply or divide by 2^N */
4 Copyright 2000, 2002 Free Software Foundation, Inc.
6 This file is part of the GNU MP Library.
8 The GNU MP Library is free software; you can redistribute it and/or modify
9 it under the terms of the GNU Lesser General Public License as published by
10 the Free Software Foundation; either version 3 of the License, or (at your
11 option) any later version.
13 The GNU MP Library is distributed in the hope that it will be useful, but
14 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
15 or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
16 License for more details.
18 You should have received a copy of the GNU Lesser General Public License
19 along with the GNU MP Library. If not, see http://www.gnu.org/licenses/. */
26 /* The multiplier/divisor "n", representing 2^n, is applied by right shifting
27 "r" until it's odd (if it isn't already), and left shifting "l" for the
31 mord_2exp (mpz_ptr ldst, mpz_ptr rdst, mpz_srcptr lsrc, mpz_srcptr rsrc,
34 mp_size_t rsrc_size = SIZ(rsrc);
35 mp_size_t len = ABS (rsrc_size);
36 mp_ptr rsrc_ptr = PTR(rsrc);
42 while (n >= GMP_NUMB_BITS && plow == 0)
49 /* no realloc here if rsrc==rdst, so p and rsrc_ptr remain valid */
50 len -= (p - rsrc_ptr);
51 MPZ_REALLOC (rdst, len);
54 if ((plow & 1) || n == 0)
56 /* need DECR when src==dst */
58 MPN_COPY_DECR (rdst_ptr, p, len);
67 count_trailing_zeros (shift, plow);
68 shift = MIN (shift, n);
70 mpn_rshift (rdst_ptr, p, len, shift);
71 len -= (rdst_ptr[len-1] == 0);
74 SIZ(rdst) = (rsrc_size >= 0) ? len : -len;
77 mpz_mul_2exp (ldst, lsrc, n);
78 else if (ldst != lsrc)
84 mpq_mul_2exp (mpq_ptr dst, mpq_srcptr src, mp_bitcnt_t n)
86 mord_2exp (mpq_numref (dst), mpq_denref (dst),
87 mpq_numref (src), mpq_denref (src), n);
91 mpq_div_2exp (mpq_ptr dst, mpq_srcptr src, mp_bitcnt_t n)
93 if (SIZ (mpq_numref(src)) == 0)
95 dst->_mp_num._mp_size = 0;
96 dst->_mp_den._mp_size = 1;
97 dst->_mp_den._mp_d[0] = 1;
101 mord_2exp (mpq_denref (dst), mpq_numref (dst),
102 mpq_denref (src), mpq_numref (src), n);