1 /* UltraSPARC 64 mpn_divexact_1 -- mpn by limb exact division.
2
3 THE FUNCTIONS IN THIS FILE ARE FOR INTERNAL USE ONLY. THEY'RE ALMOST
4 CERTAIN TO BE SUBJECT TO INCOMPATIBLE CHANGES OR DISAPPEAR COMPLETELY IN
5 FUTURE GNU MP RELEASES.
6
7 Copyright 2000, 2001, 2003, 2019 Free Software Foundation, Inc.
8
9 This file is part of the GNU MP Library.
10
11 The GNU MP Library is free software; you can redistribute it and/or modify
12 it under the terms of either:
13
14 * the GNU Lesser General Public License as published by the Free
15 Software Foundation; either version 3 of the License, or (at your
16 option) any later version.
17
18 or
19
20 * the GNU General Public License as published by the Free Software
21 Foundation; either version 2 of the License, or (at your option) any
22 later version.
23
24 or both in parallel, as here.
25
26 The GNU MP Library is distributed in the hope that it will be useful, but
27 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
28 or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
29 for more details.
30
31 You should have received copies of the GNU General Public License and the
32 GNU Lesser General Public License along with the GNU MP Library. If not,
33 see https://www.gnu.org/licenses/. */
34
35 #include "gmp-impl.h"
36 #include "longlong.h"
37
38 #include "mpn/sparc64/sparc64.h"
39
40
41 /* 64-bit divisor 32-bit divisor
42 cycles/limb cycles/limb
43 (approx) (approx)
44 Ultrasparc 2i: 110 70
45 */
46
47
48 /* There are two key ideas here to reduce mulx's. Firstly when the divisor
49 is 32-bits the high of q*d can be calculated without the two 32x32->64
50 cross-products involving the high 32-bits of the divisor, that being zero
51 of course. Secondly umul_ppmm_lowequal and umul_ppmm_half_lowequal save
52 one mulx (each) knowing the low of q*d is equal to the input limb l.
53
54 For size==1, a simple udivx is used. This is faster than calculating an
55 inverse.
56
57 For a 32-bit divisor and small sizes, an attempt was made at a simple
58 udivx loop (two per 64-bit limb), but it turned out to be slower than
59 mul-by-inverse. At size==2 the inverse is about 260 cycles total
60 compared to a udivx at 291. Perhaps the latter would suit when size==2
61 but the high 32-bits of the second limb is zero (saving one udivx), but
62 it doesn't seem worth a special case just for that. */
63
64 void
mpn_divexact_1(mp_ptr dst,mp_srcptr src,mp_size_t size,mp_limb_t divisor)65 mpn_divexact_1 (mp_ptr dst, mp_srcptr src, mp_size_t size, mp_limb_t divisor)
66 {
67 mp_limb_t inverse, s, s_next, c, l, ls, q;
68 unsigned rshift, lshift;
69 mp_limb_t lshift_mask;
70 mp_limb_t divisor_h;
71
72 ASSERT (size >= 1);
73 ASSERT (divisor != 0);
74 ASSERT (MPN_SAME_OR_SEPARATE_P (dst, src, size));
75 ASSERT_MPN (src, size);
76 ASSERT_LIMB (divisor);
77
78 s = *src++; /* src low limb */
79 size--;
80 if (size == 0)
81 {
82 *dst = s / divisor;
83 return;
84 }
85
86 if ((divisor & 1) == 0)
87 {
88 count_trailing_zeros (rshift, divisor);
89 divisor >>= rshift;
90 lshift = 64 - rshift;
91
92 lshift_mask = MP_LIMB_T_MAX;
93 }
94 else
95 {
96 rshift = 0;
97
98 /* rshift==0 means no shift, so must mask out other part in this case */
99 lshift = 0;
100 lshift_mask = 0;
101 }
102
103 binvert_limb (inverse, divisor);
104
105 c = 0;
106 divisor_h = HIGH32 (divisor);
107
108 if (divisor_h == 0)
109 {
110 /* 32-bit divisor */
111 do
112 {
113 s_next = *src++;
114 ls = (s >> rshift) | ((s_next << lshift) & lshift_mask);
115 s = s_next;
116
117 SUBC_LIMB (c, l, ls, c);
118
119 q = l * inverse;
120 *dst++ = q;
121
122 umul_ppmm_half_lowequal (l, q, divisor, l);
123 c += l;
124
125 size--;
126 }
127 while (size != 0);
128
129 ls = s >> rshift;
130 l = ls - c;
131 q = l * inverse;
132 *dst = q;
133 }
134 else
135 {
136 /* 64-bit divisor */
137 mp_limb_t divisor_l = LOW32 (divisor);
138 do
139 {
140 s_next = *src++;
141 ls = (s >> rshift) | ((s_next << lshift) & lshift_mask);
142 s = s_next;
143
144 SUBC_LIMB (c, l, ls, c);
145
146 q = l * inverse;
147 *dst++ = q;
148
149 umul_ppmm_lowequal (l, q, divisor, divisor_h, divisor_l, l);
150 c += l;
151
152 size--;
153 }
154 while (size != 0);
155
156 ls = s >> rshift;
157 l = ls - c;
158 q = l * inverse;
159 *dst = q;
160 }
161 }
162