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