1/*
2 * Copyright (C) 2007 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
17package com.android.dexgen.dex.code.form;
18
19import com.android.dexgen.dex.code.CstInsn;
20import com.android.dexgen.dex.code.DalvInsn;
21import com.android.dexgen.dex.code.InsnFormat;
22import com.android.dexgen.rop.code.RegisterSpec;
23import com.android.dexgen.rop.code.RegisterSpecList;
24import com.android.dexgen.rop.cst.Constant;
25import com.android.dexgen.rop.cst.CstMethodRef;
26import com.android.dexgen.rop.cst.CstType;
27import com.android.dexgen.rop.type.Type;
28import com.android.dexgen.util.AnnotatedOutput;
29
30/**
31 * Instruction format {@code 35c}. See the instruction format spec
32 * for details.
33 */
34public final class Form35c extends InsnFormat {
35    /** {@code non-null;} unique instance of this class */
36    public static final InsnFormat THE_ONE = new Form35c();
37
38    /** Maximal number of operands */
39    private static final int MAX_NUM_OPS = 5;
40
41    /**
42     * Constructs an instance. This class is not publicly
43     * instantiable. Use {@link #THE_ONE}.
44     */
45    private Form35c() {
46        // This space intentionally left blank.
47    }
48
49    /** {@inheritDoc} */
50    @Override
51    public String insnArgString(DalvInsn insn) {
52        RegisterSpecList regs = explicitize(insn.getRegisters());
53        return regListString(regs) + ", " + cstString(insn);
54    }
55
56    /** {@inheritDoc} */
57    @Override
58    public String insnCommentString(DalvInsn insn, boolean noteIndices) {
59        if (noteIndices) {
60            return cstComment(insn);
61        } else {
62            return "";
63        }
64    }
65
66    /** {@inheritDoc} */
67    @Override
68    public int codeSize() {
69        return 3;
70    }
71
72    /** {@inheritDoc} */
73    @Override
74    public boolean isCompatible(DalvInsn insn) {
75        if (!(insn instanceof CstInsn)) {
76            return false;
77        }
78
79        CstInsn ci = (CstInsn) insn;
80        int cpi = ci.getIndex();
81
82        if (! unsignedFitsInShort(cpi)) {
83            return false;
84        }
85
86        Constant cst = ci.getConstant();
87        if (!((cst instanceof CstMethodRef) ||
88              (cst instanceof CstType))) {
89            return false;
90        }
91
92        RegisterSpecList regs = ci.getRegisters();
93        return (wordCount(regs) >= 0);
94    }
95
96    /** {@inheritDoc} */
97    @Override
98    public InsnFormat nextUp() {
99        return Form3rc.THE_ONE;
100    }
101
102    /** {@inheritDoc} */
103    @Override
104    public void writeTo(AnnotatedOutput out, DalvInsn insn) {
105        int cpi = ((CstInsn) insn).getIndex();
106        RegisterSpecList regs = explicitize(insn.getRegisters());
107        int sz = regs.size();
108        int r0 = (sz > 0) ? regs.get(0).getReg() : 0;
109        int r1 = (sz > 1) ? regs.get(1).getReg() : 0;
110        int r2 = (sz > 2) ? regs.get(2).getReg() : 0;
111        int r3 = (sz > 3) ? regs.get(3).getReg() : 0;
112        int r4 = (sz > 4) ? regs.get(4).getReg() : 0;
113
114        write(out,
115              opcodeUnit(insn,
116                         makeByte(r4, sz)), // encode the fifth operand here
117              (short) cpi,
118              codeUnit(r0, r1, r2, r3));
119    }
120
121    /**
122     * Gets the number of words required for the given register list, where
123     * category-2 values count as two words. Return {@code -1} if the
124     * list requires more than five words or contains registers that need
125     * more than a nibble to identify them.
126     *
127     * @param regs {@code non-null;} the register list in question
128     * @return {@code >= -1;} the number of words required, or {@code -1}
129     * if the list couldn't possibly fit in this format
130     */
131    private static int wordCount(RegisterSpecList regs) {
132        int sz = regs.size();
133
134        if (sz > MAX_NUM_OPS) {
135            // It can't possibly fit.
136            return -1;
137        }
138
139        int result = 0;
140
141        for (int i = 0; i < sz; i++) {
142            RegisterSpec one = regs.get(i);
143            result += one.getCategory();
144            /*
145             * The check below adds (category - 1) to the register, to
146             * account for the fact that the second half of a
147             * category-2 register has to be represented explicitly in
148             * the result.
149             */
150            if (!unsignedFitsInNibble(one.getReg() + one.getCategory() - 1)) {
151                return -1;
152            }
153        }
154
155        return (result <= MAX_NUM_OPS) ? result : -1;
156    }
157
158    /**
159     * Returns a register list which is equivalent to the given one,
160     * except that it splits category-2 registers into two explicit
161     * entries. This returns the original list if no modification is
162     * required
163     *
164     * @param orig {@code non-null;} the original list
165     * @return {@code non-null;} the list with the described transformation
166     */
167    private static RegisterSpecList explicitize(RegisterSpecList orig) {
168        int wordCount = wordCount(orig);
169        int sz = orig.size();
170
171        if (wordCount == sz) {
172            return orig;
173        }
174
175        RegisterSpecList result = new RegisterSpecList(wordCount);
176        int wordAt = 0;
177
178        for (int i = 0; i < sz; i++) {
179            RegisterSpec one = orig.get(i);
180            result.set(wordAt, one);
181            if (one.getCategory() == 2) {
182                result.set(wordAt + 1,
183                           RegisterSpec.make(one.getReg() + 1, Type.VOID));
184                wordAt += 2;
185            } else {
186                wordAt++;
187            }
188        }
189
190        result.setImmutable();
191        return result;
192    }
193}
194