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direwolf/src/il2p_payload.c

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//
// This file is part of Dire Wolf, an amateur radio packet TNC.
//
// Copyright (C) 2021 John Langner, WB2OSZ
//
// This program 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 2 of the License, or
// (at your option) any later version.
//
// This program 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 this program. If not, see <http://www.gnu.org/licenses/>.
//
#include "direwolf.h"
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <assert.h>
#include "textcolor.h"
#include "il2p.h"
/*--------------------------------------------------------------------------------
*
* File: il2p_payload.c
*
* Purpose: Functions dealing with the payload.
*
*--------------------------------------------------------------------------------*/
/*--------------------------------------------------------------------------------
*
* Function: il2p_payload_compute
*
* Purpose: Compute number and sizes of data blocks based on total size.
*
* Inputs: payload_size 0 to 1023. (IL2P_MAX_PAYLOAD_SIZE)
* max_fec true for 16 parity symbols, false for automatic.
*
* Outputs: *p Payload block sizes and counts.
* Number of parity symbols per block.
*
* Returns: Number of bytes in the encoded format.
* Could be 0 for no payload blocks.
* -1 for error (i.e. invalid unencoded size: <0 or >1023)
*
*--------------------------------------------------------------------------------*/
int il2p_payload_compute (il2p_payload_properties_t *p, int payload_size, int max_fec)
{
memset (p, 0, sizeof(il2p_payload_properties_t));
if (payload_size < 0 || payload_size > IL2P_MAX_PAYLOAD_SIZE) {
return (-1);
}
if (payload_size == 0) {
return (0);
}
if (max_fec) {
p->payload_byte_count = payload_size;
p->payload_block_count = (p->payload_byte_count + 238) / 239;
p->small_block_size = p->payload_byte_count / p->payload_block_count;
p->large_block_size = p->small_block_size + 1;
p->large_block_count = p->payload_byte_count - (p->payload_block_count * p->small_block_size);
p->small_block_count = p->payload_block_count - p->large_block_count;
p->parity_symbols_per_block = 16;
}
else {
p->payload_byte_count = payload_size;
p->payload_block_count = (p->payload_byte_count + 246) / 247;
p->small_block_size = p->payload_byte_count / p->payload_block_count;
p->large_block_size = p->small_block_size + 1;
p->large_block_count = p->payload_byte_count - (p->payload_block_count * p->small_block_size);
p->small_block_count = p->payload_block_count - p->large_block_count;
//p->parity_symbols_per_block = (p->small_block_size / 32) + 2; // Looks like error in documentation
// It would work if the number of parity symbols was based on large block size.
if (p->small_block_size <= 61) p->parity_symbols_per_block = 2;
else if (p->small_block_size <= 123) p->parity_symbols_per_block = 4;
else if (p->small_block_size <= 185) p->parity_symbols_per_block = 6;
else if (p->small_block_size <= 247) p->parity_symbols_per_block = 8;
else {
// Should not happen. But just in case...
text_color_set(DW_COLOR_ERROR);
dw_printf ("IL2P parity symbol per payload block error. small_block_size = %d\n", p->small_block_size);
return (-1);
}
}
// Return the total size for the encoded format.
return (p->small_block_count * (p->small_block_size + p->parity_symbols_per_block) +
p->large_block_count * (p->large_block_size + p->parity_symbols_per_block));
} // end il2p_payload_compute
/*--------------------------------------------------------------------------------
*
* Function: il2p_encode_payload
*
* Purpose: Split payload into multiple blocks such that each set
* of data and parity symbols fit into a 255 byte RS block.
*
* Inputs: *payload Array of bytes.
* payload_size 0 to 1023. (IL2P_MAX_PAYLOAD_SIZE)
* max_fec true for 16 parity symbols, false for automatic.
*
* Outputs: *enc Encoded payload for transmission.
* Up to IL2P_MAX_ENCODED_SIZE bytes.
*
* Returns: -1 for error (i.e. invalid size)
* 0 for no blocks. (i.e. size zero)
* Number of bytes generated. Maximum IL2P_MAX_ENCODED_SIZE.
*
* Note: I interpretted the protocol spec as saying the LFSR state is retained
* between data blocks. During interoperability testing, I found that
* was not the case. It is reset for each data block.
*
*--------------------------------------------------------------------------------*/
int il2p_encode_payload (unsigned char *payload, int payload_size, int max_fec, unsigned char *enc)
{
if (payload_size > IL2P_MAX_PAYLOAD_SIZE) return (-1);
if (payload_size == 0) return (0);
// Determine number of blocks and sizes.
il2p_payload_properties_t ipp;
int e;
e = il2p_payload_compute (&ipp, payload_size, max_fec);
if (e <= 0) {
return (e);
}
unsigned char *pin = payload;
unsigned char *pout = enc;
int encoded_length = 0;
unsigned char scram[256];
unsigned char parity[IL2P_MAX_PARITY_SYMBOLS];
// First the large blocks.
for (int b = 0; b < ipp.large_block_count; b++) {
il2p_scramble_block (pin, scram, ipp.large_block_size);
memcpy (pout, scram, ipp.large_block_size);
pin += ipp.large_block_size;
pout += ipp.large_block_size;
encoded_length += ipp.large_block_size;
il2p_encode_rs (scram, ipp.large_block_size, ipp.parity_symbols_per_block, parity);
memcpy (pout, parity, ipp.parity_symbols_per_block);
pout += ipp.parity_symbols_per_block;
encoded_length += ipp.parity_symbols_per_block;
}
// Then the small blocks.
for (int b = 0; b < ipp.small_block_count; b++) {
il2p_scramble_block (pin, scram, ipp.small_block_size);
memcpy (pout, scram, ipp.small_block_size);
pin += ipp.small_block_size;
pout += ipp.small_block_size;
encoded_length += ipp.small_block_size;
il2p_encode_rs (scram, ipp.small_block_size, ipp.parity_symbols_per_block, parity);
memcpy (pout, parity, ipp.parity_symbols_per_block);
pout += ipp.parity_symbols_per_block;
encoded_length += ipp.parity_symbols_per_block;
}
return (encoded_length);
} // end il2p_encode_payload
/*--------------------------------------------------------------------------------
*
* Function: il2p_decode_payload
*
* Purpose: Extract original data from encoded payload.
*
* Inputs: received Array of bytes. Size is unknown but in practice it
* must not exceeed IL2P_MAX_ENCODED_SIZE.
* payload_size 0 to 1023. (IL2P_MAX_PAYLOAD_SIZE)
* Expected result size based on header.
* max_fec true for 16 parity symbols, false for automatic.
*
* Outputs: payload_out Recovered payload.
*
* In/Out: symbols_corrected Number of symbols corrected.
*
*
* Returns: Number of bytes extracted. Should be same as payload_size going in.
* -3 for unexpected internal inconsistency.
* -2 for unable to recover from signal corruption.
* -1 for invalid size.
* 0 for no blocks. (i.e. size zero)
*
* Description: Each block is scrambled separately but the LSFR state is carried
* from the first payload block to the next.
*
*--------------------------------------------------------------------------------*/
int il2p_decode_payload (unsigned char *received, int payload_size, int max_fec, unsigned char *payload_out, int *symbols_corrected)
{
// Determine number of blocks and sizes.
il2p_payload_properties_t ipp;
int e;
e = il2p_payload_compute (&ipp, payload_size, max_fec);
if (e <= 0) {
return (e);
}
unsigned char *pin = received;
unsigned char *pout = payload_out;
int decoded_length = 0;
int failed = 0;
// First the large blocks.
for (int b = 0; b < ipp.large_block_count; b++) {
unsigned char corrected_block[255];
int e = il2p_decode_rs (pin, ipp.large_block_size, ipp.parity_symbols_per_block, corrected_block);
// dw_printf ("%s:%d: large block decode_rs returned status = %d\n", __FILE__, __LINE__, e);
if (e < 0) failed = 1;
*symbols_corrected += e;
il2p_descramble_block (corrected_block, pout, ipp.large_block_size);
if (il2p_get_debug() >= 2) {
text_color_set(DW_COLOR_DEBUG);
dw_printf ("Descrambled large payload block, %d bytes:\n", ipp.large_block_size);
fx_hex_dump(pout, ipp.large_block_size);
}
pin += ipp.large_block_size + ipp.parity_symbols_per_block;
pout += ipp.large_block_size;
decoded_length += ipp.large_block_size;
}
// Then the small blocks.
for (int b = 0; b < ipp.small_block_count; b++) {
unsigned char corrected_block[255];
int e = il2p_decode_rs (pin, ipp.small_block_size, ipp.parity_symbols_per_block, corrected_block);
// dw_printf ("%s:%d: small block decode_rs returned status = %d\n", __FILE__, __LINE__, e);
if (e < 0) failed = 1;
*symbols_corrected += e;
il2p_descramble_block (corrected_block, pout, ipp.small_block_size);
if (il2p_get_debug() >= 2) {
text_color_set(DW_COLOR_DEBUG);
dw_printf ("Descrambled small payload block, %d bytes:\n", ipp.small_block_size);
fx_hex_dump(pout, ipp.small_block_size);
}
pin += ipp.small_block_size + ipp.parity_symbols_per_block;
pout += ipp.small_block_size;
decoded_length += ipp.small_block_size;
}
if (failed) {
//dw_printf ("%s:%d: failed = %0x\n", __FILE__, __LINE__, failed);
return (-2);
}
if (decoded_length != payload_size) {
text_color_set(DW_COLOR_ERROR);
dw_printf ("IL2P Internal error: decoded_length = %d, payload_size = %d\n", decoded_length, payload_size);
return (-3);
}
return (decoded_length);
} // end il2p_decode_payload
// end il2p_payload.c
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