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
17package com.android.internal.midi;
18
19/**
20 * MIDI related constants and static methods.
21 */
22public final class MidiConstants {
23    public static final byte STATUS_COMMAND_MASK = (byte) 0xF0;
24    public static final byte STATUS_CHANNEL_MASK = (byte) 0x0F;
25
26    // Channel voice messages.
27    public static final byte STATUS_NOTE_OFF = (byte) 0x80;
28    public static final byte STATUS_NOTE_ON = (byte) 0x90;
29    public static final byte STATUS_POLYPHONIC_AFTERTOUCH = (byte) 0xA0;
30    public static final byte STATUS_CONTROL_CHANGE = (byte) 0xB0;
31    public static final byte STATUS_PROGRAM_CHANGE = (byte) 0xC0;
32    public static final byte STATUS_CHANNEL_PRESSURE = (byte) 0xD0;
33    public static final byte STATUS_PITCH_BEND = (byte) 0xE0;
34
35    // System Common Messages.
36    public static final byte STATUS_SYSTEM_EXCLUSIVE = (byte) 0xF0;
37    public static final byte STATUS_MIDI_TIME_CODE = (byte) 0xF1;
38    public static final byte STATUS_SONG_POSITION = (byte) 0xF2;
39    public static final byte STATUS_SONG_SELECT = (byte) 0xF3;
40    public static final byte STATUS_TUNE_REQUEST = (byte) 0xF6;
41    public static final byte STATUS_END_SYSEX = (byte) 0xF7;
42
43    // System Real-Time Messages
44    public static final byte STATUS_TIMING_CLOCK = (byte) 0xF8;
45    public static final byte STATUS_START = (byte) 0xFA;
46    public static final byte STATUS_CONTINUE = (byte) 0xFB;
47    public static final byte STATUS_STOP = (byte) 0xFC;
48    public static final byte STATUS_ACTIVE_SENSING = (byte) 0xFE;
49    public static final byte STATUS_RESET = (byte) 0xFF;
50
51    /** Number of bytes in a message nc from 8c to Ec */
52    public final static int CHANNEL_BYTE_LENGTHS[] = { 3, 3, 3, 3, 2, 2, 3 };
53
54    /** Number of bytes in a message Fn from F0 to FF */
55    public final static int SYSTEM_BYTE_LENGTHS[] = { 1, 2, 3, 2, 1, 1, 1, 1, 1,
56            1, 1, 1, 1, 1, 1, 1 };
57
58
59    /**
60     * MIDI messages, except for SysEx, are 1,2 or 3 bytes long.
61     * You can tell how long a MIDI message is from the first status byte.
62     * Do not call this for SysEx, which has variable length.
63     * @param statusByte
64     * @return number of bytes in a complete message or zero if data byte passed
65     */
66    public static int getBytesPerMessage(byte statusByte) {
67        // Java bytes are signed so we need to mask off the high bits
68        // to get a value between 0 and 255.
69        int statusInt = statusByte & 0xFF;
70        if (statusInt >= 0xF0) {
71            // System messages use low nibble for size.
72            return SYSTEM_BYTE_LENGTHS[statusInt & 0x0F];
73        } else if(statusInt >= 0x80) {
74            // Channel voice messages use high nibble for size.
75            return CHANNEL_BYTE_LENGTHS[(statusInt >> 4) - 8];
76        } else {
77            return 0; // data byte
78        }
79    }
80
81
82    /**
83     * @param msg
84     * @param offset
85     * @param count
86     * @return true if the entire message is ActiveSensing commands
87     */
88    public static boolean isAllActiveSensing(byte[] msg, int offset,
89            int count) {
90        // Count bytes that are not active sensing.
91        int goodBytes = 0;
92        for (int i = 0; i < count; i++) {
93            byte b = msg[offset + i];
94            if (b != MidiConstants.STATUS_ACTIVE_SENSING) {
95                goodBytes++;
96            }
97        }
98        return (goodBytes == 0);
99    }
100
101    // Returns true if this command can be used for running status
102    public static boolean allowRunningStatus(byte command) {
103        // only Channel Voice and Channel Mode commands can use running status
104        return (command >= STATUS_NOTE_OFF && command < STATUS_SYSTEM_EXCLUSIVE);
105    }
106
107    // Returns true if this command cancels running status
108    public static boolean cancelsRunningStatus(byte command) {
109        // System Common messages cancel running status
110        return (command >= STATUS_SYSTEM_EXCLUSIVE && command <= STATUS_END_SYSEX);
111    }
112}
113