1 /* mpn_mod_1(dividend_ptr, dividend_size, divisor_limb) --
2 Divide (DIVIDEND_PTR,,DIVIDEND_SIZE) by DIVISOR_LIMB.
3 Return the single-limb remainder.
4 There are no constraints on the value of the divisor.
6 Copyright (C) 1991, 1993, 1994, 1999 Free Software Foundation, Inc.
8 This file is part of the GNU MP Library.
10 The GNU MP Library is free software; you can redistribute it and/or modify
11 it under the terms of the GNU Lesser General Public License as published by
12 the Free Software Foundation; either version 2.1 of the License, or (at your
13 option) any later version.
15 The GNU MP Library is distributed in the hope that it will be useful, but
16 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
17 or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
18 License for more details.
20 You should have received a copy of the GNU Lesser General Public License
21 along with the GNU MP Library; see the file COPYING.LIB. If not, write to
22 the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
23 MA 02111-1307, USA. */
34 #define UDIV_TIME UMUL_TIME
39 mpn_mod_1 (mp_srcptr dividend_ptr, mp_size_t dividend_size,
40 mp_limb_t divisor_limb)
42 mpn_mod_1 (dividend_ptr, dividend_size, divisor_limb)
43 mp_srcptr dividend_ptr;
44 mp_size_t dividend_size;
45 mp_limb_t divisor_limb;
52 /* Botch: Should this be handled at all? Rely on callers? */
53 if (dividend_size == 0)
56 /* If multiplication is much faster than division, and the
57 dividend is large, pre-invert the divisor, and use
58 only multiplications in the inner loop. */
60 /* This test should be read:
61 Does it ever help to use udiv_qrnnd_preinv?
62 && Does what we save compensate for the inversion overhead? */
63 if (UDIV_TIME > (2 * UMUL_TIME + 6)
64 && (UDIV_TIME - (2 * UMUL_TIME + 6)) * dividend_size > UDIV_TIME)
66 int normalization_steps;
68 count_leading_zeros (normalization_steps, divisor_limb);
69 if (normalization_steps != 0)
71 mp_limb_t divisor_limb_inverted;
73 divisor_limb <<= normalization_steps;
74 invert_limb (divisor_limb_inverted, divisor_limb);
76 n1 = dividend_ptr[dividend_size - 1];
77 r = n1 >> (BITS_PER_MP_LIMB - normalization_steps);
79 /* Possible optimization:
81 && divisor_limb > ((n1 << normalization_steps)
82 | (dividend_ptr[dividend_size - 2] >> ...)))
83 ...one division less... */
85 for (i = dividend_size - 2; i >= 0; i--)
88 udiv_qrnnd_preinv (dummy, r, r,
89 ((n1 << normalization_steps)
90 | (n0 >> (BITS_PER_MP_LIMB - normalization_steps))),
91 divisor_limb, divisor_limb_inverted);
94 udiv_qrnnd_preinv (dummy, r, r,
95 n1 << normalization_steps,
96 divisor_limb, divisor_limb_inverted);
97 return r >> normalization_steps;
101 mp_limb_t divisor_limb_inverted;
103 invert_limb (divisor_limb_inverted, divisor_limb);
105 i = dividend_size - 1;
108 if (r >= divisor_limb)
115 n0 = dividend_ptr[i];
116 udiv_qrnnd_preinv (dummy, r, r,
117 n0, divisor_limb, divisor_limb_inverted);
124 if (UDIV_NEEDS_NORMALIZATION)
126 int normalization_steps;
128 count_leading_zeros (normalization_steps, divisor_limb);
129 if (normalization_steps != 0)
131 divisor_limb <<= normalization_steps;
133 n1 = dividend_ptr[dividend_size - 1];
134 r = n1 >> (BITS_PER_MP_LIMB - normalization_steps);
136 /* Possible optimization:
138 && divisor_limb > ((n1 << normalization_steps)
139 | (dividend_ptr[dividend_size - 2] >> ...)))
140 ...one division less... */
142 for (i = dividend_size - 2; i >= 0; i--)
144 n0 = dividend_ptr[i];
145 udiv_qrnnd (dummy, r, r,
146 ((n1 << normalization_steps)
147 | (n0 >> (BITS_PER_MP_LIMB - normalization_steps))),
151 udiv_qrnnd (dummy, r, r,
152 n1 << normalization_steps,
154 return r >> normalization_steps;
157 /* No normalization needed, either because udiv_qrnnd doesn't require
158 it, or because DIVISOR_LIMB is already normalized. */
160 i = dividend_size - 1;
163 if (r >= divisor_limb)
170 n0 = dividend_ptr[i];
171 udiv_qrnnd (dummy, r, r, n0, divisor_limb);