245 lines
6.7 KiB
C++
245 lines
6.7 KiB
C++
#include <tuple>
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#include <optional>
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#include <cstdint>
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#include <bit>
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#include "parse.hpp"
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namespace midi {
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namespace parse {
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static constexpr inline std::optional<std::tuple<buf_t, uint32_t>>
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int_variable_length(buf_t buf)
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{
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uint32_t n = 0;
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int32_t i = 0;
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while (i < 4) {
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n <<= 7;
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uint8_t b = buf[i++];
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n |= (b & 0x7f);
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if ((b & 0x80) == 0)
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return {{buf + i, n}};
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}
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return std::nullopt;
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}
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static constexpr inline std::tuple<buf_t, uint16_t>
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int_fixed_length16(buf_t buf)
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{
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uint16_t n;
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if constexpr (std::endian::native == std::endian::big) {
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n = *reinterpret_cast<const uint16_t*>(buf);
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} else {
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n = (buf[0] << 8 | buf[1] << 0);
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}
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return {buf + (sizeof (uint16_t)), n};
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}
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static constexpr inline std::tuple<buf_t, uint32_t>
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int_fixed_length32(buf_t buf)
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{
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uint32_t n;
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if constexpr (std::endian::native == std::endian::big) {
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n = *reinterpret_cast<const uint32_t*>(buf);
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} else {
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n = (buf[0] << 24 | buf[1] << 16 | buf[2] << 8 | buf[3] << 0);
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}
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return {buf + (sizeof (uint32_t)), n};
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}
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static constexpr inline std::optional<buf_t>
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header_chunk_type(buf_t buf)
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{
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if ( buf[0] == 'M'
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&& buf[1] == 'T'
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&& buf[2] == 'h'
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&& buf[3] == 'd')
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return {buf + 4};
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else
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return std::nullopt;
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}
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static constexpr inline std::tuple<buf_t, division_t>
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division(buf_t buf)
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{
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uint16_t n;
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std::tie(buf, n) = int_fixed_length16(buf);
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if ((n & (1 << 15)) != 0) {
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int8_t smpte = ((n >> 8) & 0x7f) - 0x80; // sign-extend
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uint8_t ticks_per_frame = n & 0xff;
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return { buf, { .type = division_t::type_t::time_code,
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.time_code = { smpte, ticks_per_frame }
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} };
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} else {
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return { buf, { .type = division_t::type_t::metrical,
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.metrical = { n }
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} };
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}
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}
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std::optional<std::tuple<buf_t, header_t>>
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header(buf_t buf)
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{
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auto buf_o = header_chunk_type(buf);
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if (!buf_o) return std::nullopt;
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buf = *buf_o;
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uint32_t header_length;
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std::tie(buf, header_length) = int_fixed_length32(buf);
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if (header_length != 6) return std::nullopt;
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uint16_t format_num;
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std::tie(buf, format_num) = int_fixed_length16(buf);
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header_t::format_t format;
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switch (format_num) {
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case 0: format = header_t::format_t::_0; break;
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case 1: format = header_t::format_t::_1; break;
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case 2: format = header_t::format_t::_2; break;
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default: return std::nullopt;
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}
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uint16_t ntrks;
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std::tie(buf, ntrks) = int_fixed_length16(buf);
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division_t division;
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std::tie(buf, division) = parse::division(buf);
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return {{buf, {format, ntrks, division}}};
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}
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static constexpr inline std::optional<std::tuple<buf_t, midi_event_t::type_t>>
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midi_event_type(buf_t buf)
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{
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uint8_t n = buf[0] & 0xf0;
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// do not increment buf; the caller needs to parse channel
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switch (n) {
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case 0x80: return {{buf, midi_event_t::type_t::note_off}};
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case 0x90: return {{buf, midi_event_t::type_t::note_on}};
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case 0xa0: return {{buf, midi_event_t::type_t::polyphonic_key_pressure}};
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case 0xb0:
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if (buf[0] >= 121 && buf[0] <= 127)
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return {{buf, midi_event_t::type_t::channel_mode}};
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else
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return {{buf, midi_event_t::type_t::control_change}};
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case 0xc0: return {{buf, midi_event_t::type_t::program_change}};
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case 0xd0: return {{buf, midi_event_t::type_t::channel_pressure}};
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case 0xe0: return {{buf, midi_event_t::type_t::pitch_bend_change}};
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default: return std::nullopt;
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};
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}
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static constexpr inline int32_t
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midi_event_message_length(midi_event_t::type_t type)
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{
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if (type == midi_event_t::type_t::program_change || type == midi_event_t::type_t::channel_pressure)
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return 1;
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else
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return 2;
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}
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static constexpr inline std::optional<std::tuple<buf_t, midi_event_t>>
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midi_event(buf_t buf)
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{
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// it doesn't matter which union is used, as long as it is one with
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// 3 items. note_off is used throughout, even though it could
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// represent a type other than note_off.
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midi_event_t event;
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auto type_o = midi_event_type(buf); // does not increment buf
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if (!type_o) return std::nullopt;
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std::tie(buf, event.type) = *type_o;
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event.data.note_off.channel = buf[0] & 0x0f;
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event.data.note_off.note = buf[1];
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// possibly-initializing the third field on a 2-field midi_event
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// does not matter, as the caller should ignore it anyway. This
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// harmless extraneous initialization means a branch is not needed.
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event.data.note_off.velocity = buf[2];
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buf += 1 + midi_event_message_length(event.type);
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// this does not validate that buf[1]/buf[2] are <= 0x7f
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return {{buf, event}};
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}
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static constexpr inline std::optional<std::tuple<buf_t, sysex_event_t>>
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sysex_event(buf_t buf)
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{
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if (buf[0] != 0xf0 && buf[0] != 0xf7) return std::nullopt;
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buf++;
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auto length_o = int_variable_length(buf);
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if (!length_o) return std::nullopt;
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uint32_t length;
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std::tie(buf, length) = *length_o;
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return {{buf + length, {buf, length}}};
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}
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static constexpr inline std::optional<std::tuple<buf_t, meta_event_t>>
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meta_event(buf_t buf)
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{
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if (buf[0] != 0xff) return std::nullopt;
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uint8_t type = buf[1];
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buf += 2;
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auto length_o = int_variable_length(buf);
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if (!length_o) return std::nullopt;
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uint32_t length;
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std::tie(buf, length) = *length_o;
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return {{buf + length, {buf, length, type}}};
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}
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static constexpr inline std::optional<std::tuple<buf_t, event_t>>
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event(buf_t buf)
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{
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if (auto midi_o = midi_event(buf)) {
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midi_event_t midi;
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std::tie(buf, midi) = *midi_o;
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return {{buf, {event_t::type_t::midi, {.midi = midi}}}};
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} else if (auto meta_o = meta_event(buf)) {
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meta_event_t meta;
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std::tie(buf, meta) = *meta_o;
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return {{buf, {event_t::type_t::meta, {.meta = meta}}}};
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} else if (auto sysex_o = sysex_event(buf)) {
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sysex_event_t sysex;
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std::tie(buf, sysex) = *sysex_o;
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return {{buf, {event_t::type_t::sysex, {.sysex = sysex}}}};
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} else {
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return std::nullopt;
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}
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}
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std::optional<std::tuple<buf_t, mtrk_event_t>>
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mtrk_event(buf_t buf)
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{
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auto delta_time_o = int_variable_length(buf);
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if (!delta_time_o) return std::nullopt;
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uint32_t delta_time;
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std::tie(buf, delta_time) = *delta_time_o;
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auto event_o = event(buf);
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if (!event_o) return std::nullopt;
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event_t event;
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std::tie(buf, event) = *event_o;
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return {{buf, {delta_time, event}}};
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}
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static constexpr inline std::optional<buf_t>
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track_chunk_type(buf_t buf)
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{
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if ( buf[0] == 'M'
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&& buf[1] == 'T'
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&& buf[2] == 'r'
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&& buf[3] == 'k')
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return {buf + 4};
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else
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return std::nullopt;
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}
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std::optional<std::tuple<buf_t, uint32_t>>
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track(buf_t buf)
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{
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auto buf_o = track_chunk_type(buf);
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if (!buf_o) return std::nullopt;
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buf = *buf_o;
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uint32_t length;
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std::tie(buf, length) = int_fixed_length32(buf);
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return {{buf, length}};
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}
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} // namespace parse
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} // namespace midi
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