src/media/audio/drivers/usb-audio/midi.cc

// Copyright 2016 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "midi.h"

#include <assert.h>
#include <stdint.h>
#include <zircon/compiler.h>

#include <array>
#include <iterator>

// Number of bytes in a message nc from 8c to Ec
static const int CHANNEL_BYTE_LENGTHS[] = {3, 3, 3, 3, 2, 2, 3};

// Number of bytes in a message Fn from F0 to FF */
static const int SYSTEM_BYTE_LENGTHS[] = {1, 2, 3, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1};

int get_midi_message_length(uint8_t status_byte) {
  if (status_byte >= 0xF0) {
    // System messages use low nibble for size.
    static_assert(std::size(SYSTEM_BYTE_LENGTHS) >= 16, "SYSTEM_BYTE_LENGTHS too small");
    return SYSTEM_BYTE_LENGTHS[status_byte & 0x0F];
  } else if (status_byte >= 0x80) {
    // Channel voice messages use high nibble for size.
    static_assert(std::size(CHANNEL_BYTE_LENGTHS) >= 0xE - 8, "CHANNEL_BYTE_LENGTHS too small");
    return CHANNEL_BYTE_LENGTHS[(status_byte >> 4) - 8];
  } else {
    return 0;  // data byte
  }
}