qmk_firmware/tmk_core/protocol/midi/sysex_tools.c

// midi for embedded chips,
// Copyright 2010 Alex Norman
//
// This file is part of avr-midi.
//
// avr-midi is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
//(at your option) any later version.
//
// avr-midi is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with avr-midi.  If not, see <http://www.gnu.org/licenses/>.

#include "sysex_tools.h"

uint16_t sysex_encoded_length(uint16_t decoded_length) {
    uint8_t remainder = decoded_length % 7;
    if (remainder)
        return (decoded_length / 7) * 8 + remainder + 1;
    else
        return (decoded_length / 7) * 8;
}

uint16_t sysex_decoded_length(uint16_t encoded_length) {
    uint8_t remainder = encoded_length % 8;
    if (remainder)
        return (encoded_length / 8) * 7 + remainder - 1;
    else
        return (encoded_length / 8) * 7;
}

uint16_t sysex_encode(uint8_t *encoded, const uint8_t *source, const uint16_t length) {
    uint16_t encoded_full = length / 7;  // number of full 8 byte sections from 7 bytes of input
    uint16_t i, j;

    // fill out the fully encoded sections
    for (i = 0; i < encoded_full; i++) {
        uint16_t encoded_msb_idx = i * 8;
        uint16_t input_start_idx = i * 7;
        encoded[encoded_msb_idx] = 0;
        for (j = 0; j < 7; j++) {
            uint8_t current = source[input_start_idx + j];
            encoded[encoded_msb_idx] |= (0x80 & current) >> (1 + j);
            encoded[encoded_msb_idx + 1 + j] = 0x7F & current;
        }
    }

    // fill out the rest if there is any more
    uint8_t remainder = length % 7;
    if (remainder) {
        uint16_t encoded_msb_idx = encoded_full * 8;
        uint16_t input_start_idx = encoded_full * 7;
        encoded[encoded_msb_idx] = 0;
        for (j = 0; j < remainder; j++) {
            uint8_t current = source[input_start_idx + j];
            encoded[encoded_msb_idx] |= (0x80 & current) >> (1 + j);
            encoded[encoded_msb_idx + 1 + j] = 0x7F & current;
        }
        return encoded_msb_idx + remainder + 1;
    } else {
        return encoded_full * 8;
    }
}

uint16_t sysex_decode(uint8_t *decoded, const uint8_t *source, const uint16_t length) {
    uint16_t decoded_full = length / 8;
    uint16_t i, j;

    if (length < 2) return 0;

    // fill out the fully encoded sections
    for (i = 0; i < decoded_full; i++) {
        uint16_t encoded_msb_idx    = i * 8;
        uint16_t output_start_index = i * 7;
        for (j = 0; j < 7; j++) {
            decoded[output_start_index + j] = 0x7F & source[encoded_msb_idx + j + 1];
            decoded[output_start_index + j] |= (0x80 & (source[encoded_msb_idx] << (1 + j)));
        }
    }
    uint8_t remainder = length % 8;
    if (remainder) {
        uint16_t encoded_msb_idx    = decoded_full * 8;
        uint16_t output_start_index = decoded_full * 7;
        for (j = 0; j < (remainder - 1); j++) {
            decoded[output_start_index + j] = 0x7F & source[encoded_msb_idx + j + 1];
            decoded[output_start_index + j] |= (0x80 & (source[encoded_msb_idx] << (1 + j)));
        }
        return decoded_full * 7 + remainder - 1;
    } else {
        return decoded_full * 7;
    }
}