1 /*
2 * Copyright (C) 2015 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17 #include "code_generator_utils.h"
18
19 #include <android-base/logging.h>
20
21 #include "nodes.h"
22
23 namespace art {
24
CalculateMagicAndShiftForDivRem(int64_t divisor,bool is_long,int64_t * magic,int * shift)25 void CalculateMagicAndShiftForDivRem(int64_t divisor, bool is_long,
26 int64_t* magic, int* shift) {
27 // It does not make sense to calculate magic and shift for zero divisor.
28 DCHECK_NE(divisor, 0);
29
30 /* Implementation according to H.S.Warren's "Hacker's Delight" (Addison Wesley, 2002)
31 * Chapter 10 and T.Grablund, P.L.Montogomery's "Division by Invariant Integers Using
32 * Multiplication" (PLDI 1994).
33 * The magic number M and shift S can be calculated in the following way:
34 * Let nc be the most positive value of numerator(n) such that nc = kd - 1,
35 * where divisor(d) >= 2.
36 * Let nc be the most negative value of numerator(n) such that nc = kd + 1,
37 * where divisor(d) <= -2.
38 * Thus nc can be calculated like:
39 * nc = exp + exp % d - 1, where d >= 2 and exp = 2^31 for int or 2^63 for long
40 * nc = -exp + (exp + 1) % d, where d >= 2 and exp = 2^31 for int or 2^63 for long
41 *
42 * So the shift p is the smallest p satisfying
43 * 2^p > nc * (d - 2^p % d), where d >= 2
44 * 2^p > nc * (d + 2^p % d), where d <= -2.
45 *
46 * The magic number M is calculated by
47 * M = (2^p + d - 2^p % d) / d, where d >= 2
48 * M = (2^p - d - 2^p % d) / d, where d <= -2.
49 *
50 * Notice that p is always bigger than or equal to 32 (resp. 64), so we just return 32 - p
51 * (resp. 64 - p) as the shift number S.
52 */
53
54 int64_t p = is_long ? 63 : 31;
55 const uint64_t exp = is_long ? (UINT64_C(1) << 63) : (UINT32_C(1) << 31);
56
57 // Initialize the computations.
58 uint64_t abs_d = (divisor >= 0) ? divisor : -divisor;
59 uint64_t sign_bit = is_long ? static_cast<uint64_t>(divisor) >> 63 :
60 static_cast<uint32_t>(divisor) >> 31;
61 uint64_t tmp = exp + sign_bit;
62 uint64_t abs_nc = tmp - 1 - (tmp % abs_d);
63 uint64_t quotient1 = exp / abs_nc;
64 uint64_t remainder1 = exp % abs_nc;
65 uint64_t quotient2 = exp / abs_d;
66 uint64_t remainder2 = exp % abs_d;
67
68 /*
69 * To avoid handling both positive and negative divisor, "Hacker's Delight"
70 * introduces a method to handle these 2 cases together to avoid duplication.
71 */
72 uint64_t delta;
73 do {
74 p++;
75 quotient1 = 2 * quotient1;
76 remainder1 = 2 * remainder1;
77 if (remainder1 >= abs_nc) {
78 quotient1++;
79 remainder1 = remainder1 - abs_nc;
80 }
81 quotient2 = 2 * quotient2;
82 remainder2 = 2 * remainder2;
83 if (remainder2 >= abs_d) {
84 quotient2++;
85 remainder2 = remainder2 - abs_d;
86 }
87 delta = abs_d - remainder2;
88 } while (quotient1 < delta || (quotient1 == delta && remainder1 == 0));
89
90 *magic = (divisor > 0) ? (quotient2 + 1) : (-quotient2 - 1);
91
92 if (!is_long) {
93 *magic = static_cast<int>(*magic);
94 }
95
96 *shift = is_long ? p - 64 : p - 32;
97 }
98
IsBooleanValueOrMaterializedCondition(HInstruction * cond_input)99 bool IsBooleanValueOrMaterializedCondition(HInstruction* cond_input) {
100 return !cond_input->IsCondition() || !cond_input->IsEmittedAtUseSite();
101 }
102
103 } // namespace art
104