ua1zbe
/
dsd-fme-01.09.2024
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

M17 - Repack LSF Frame Before New Encoding Session;

This commit is contained in:
lwvmobile 2024-03-06 13:14:07 -05:00
parent 7ea26b68e7
commit 0d09baee3c
1 changed files with 35 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

35
src/m17.c
View File

@ -1711,6 +1711,11 @@ void encodeM17STR(dsd_opts * opts, dsd_state * state)
nonce[12] = rand() & 0xFF;
nonce[13] = rand() & 0xFF;
//debug print nonce
// fprintf (stderr, "\n nonce:");
// for (i = 0; i < 14; i++)
// fprintf (stderr, " %02X", nonce[i]);
//load the nonce from packed bytes to a bitwise iv array
memset(iv, 0, sizeof(iv));
k = 0;
@ -1735,6 +1740,36 @@ void encodeM17STR(dsd_opts * opts, dsd_state * state)
//attach the crc16 bits to the end of the LSF data
for (i = 0; i < 16; i++) m17_lsf[224+i] = (crc_cmp >> 15-i) & 1;
//Recraft and Prepare New LSF frame for next encoding session
//this is primarily to make sure the LSF has the refreshed nonce
memset (m17_lsfc, 0, sizeof(m17_lsfc));
memset (m17_lsfp, 0, sizeof(m17_lsfp));
memset (m17_lsfi, 0, sizeof(m17_lsfi));
memset (m17_lsfs, 0, sizeof(m17_lsfs));
//Use the convolutional encoder to encode the LSF Frame
simple_conv_encoder (m17_lsf, m17_lsfc, 244);
//P1 puncture
x = 0;
for (i = 0; i < 488; i++)
{
if (p1[i%61] == 1)
m17_lsfp[x++] = m17_lsfc[i];
}
//interleave the bit array using Quadratic Permutation Polynomial
//function π(x) = (45x + 92x^2 ) mod 368
for (i = 0; i < 368; i++)
{
x = ((45*i)+(92*i*i)) % 368;
m17_lsfi[x] = m17_lsfp[i];
}
//scramble/randomize the frame
for (i = 0; i < 368; i++)
m17_lsfs[i] = (m17_lsfi[i] ^ m17_scramble[i]) & 1;
//flush the last frame with the eot bit on
if (eot)
{