ft8_lib/ft8/v1/unpack.cpp

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#include "unpack.h"
#include "text.h"
#include <string.h>
constexpr uint32_t NBASE = 37L*36L*10L*27L*27L*27L;
// convert packed character to ASCII character
// 0..9 a..z space +-./?
char charn(uint8_t c) {
if (c >= 0 && c <= 9)
return '0' + c;
if (c >= 10 && c < 36)
return 'A' + c - 10;
if (c < 42)
return " +-./?" [c - 36];
return ' ';
}
// nc is a 28-bit integer, e.g. nc1 or nc2, containing all the
// call sign bits from a packed message.
void unpackcall(uint32_t nc, char *callsign) {
callsign[5] = charn((nc % 27) + 10); // + 10 b/c only alpha+space
nc /= 27;
callsign[4] = charn((nc % 27) + 10);
nc /= 27;
callsign[3] = charn((nc % 27) + 10);
nc /= 27;
callsign[2] = charn(nc % 10); // digit only
nc /= 10;
callsign[1] = charn(nc % 36); // letter or digit
nc /= 36;
callsign[0] = charn(nc);
callsign[6] = 0;
}
// extract maidenhead locator
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void unpackgrid(uint16_t ng, char *grid) {
// start of special grid locators for sig strength &c.
constexpr uint16_t NGBASE = 180*180;
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if (ng == NGBASE + 1) {
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// Empty grid is allowed
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grid[0] = 0;
return;
}
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// Check for signal strength reports (-01 to -30 dB)
if (ng >= NGBASE + 1 && ng < NGBASE + 31) {
int_to_dd(grid, ((NGBASE + 1) - ng), 2);
return;
}
if (ng >= NGBASE + 31 && ng < NGBASE + 62) {
grid[0] = 'R';
int_to_dd(grid + 1, ((NGBASE + 31) - ng), 2);
return;
}
// Check for special cases
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if (ng == NGBASE + 62) {
strcpy(grid, "RO");
return;
}
if (ng == NGBASE + 63) {
strcpy(grid, "RRR");
return;
}
if (ng == NGBASE + 64) {
strcpy(grid, "73");
return;
}
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// Decode 4-symbol grid
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int16_t lat = (int16_t)(ng % 180) - 90;
int16_t lng = ((int16_t)(ng / 180) * 2) - 180;
grid[0] = 'A' + ((179 - lng) / 20);
grid[1] = 'A' + ((90 + lat) / 10);
grid[2] = '0' + (((179 - lng) % 20) / 2);
grid[3] = '0' + ((90 + lat) % 10);
grid[4] = 0;
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// Check for extended range signal reports
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if ((grid[0] == 'K') && (grid[1] == 'A')) {
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int sig = dd_to_int(grid + 2, 2) - 50;
int_to_dd(grid, sig, 2);
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return;
}
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if ((grid[0] == 'L') && (grid[1] == 'A')) {
int sig = dd_to_int(grid + 2, 2) - 50;
grid[0] = 'R';
int_to_dd(grid + 1, sig, 2);
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return;
}
}
void unpacktext(uint32_t nc1, uint32_t nc2, uint16_t ng, char *text) {
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uint32_t nc3 = (ng & 0x7FFF);
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// Check for bit 0 and copy it to nc3
if ((nc1 & 1) != 0)
nc3 |= 0x08000;
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if ((nc2 & 1) != 0)
nc3 |= 0x10000;
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nc1 >>= 1;
nc2 >>= 1;
for (int i = 4; i >= 0; --i) {
text[i] = charn(nc1 % 42);
nc1 /= 42;
}
for (int i = 9; i >= 5; --i) {
text[i] = charn(nc2 % 42);
nc2 /= 42;
}
for (int i = 12; i >= 10; --i) {
text[i] = charn(nc3 % 42);
nc3 /= 42;
}
text[13] = 0;
}
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// message should have at least 19 bytes allocated (18 characters + zero terminator)
int unpack(const uint8_t *a72, char *message) {
uint32_t nc1, nc2;
uint16_t ng;
nc1 = (a72[0] << 20);
nc1 |= (a72[1] << 12);
nc1 |= (a72[2] << 4);
nc1 |= (a72[3] >> 4);
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nc2 = ((a72[3] & 0x0F) << 24);
nc2 |= (a72[4] << 16);
nc2 |= (a72[5] << 8);
nc2 |= (a72[6]);
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ng = (a72[7] << 8);
ng |= (a72[8]);
if (ng & 0x8000) {
unpacktext(nc1, nc2, ng, message);
return 0;
}
char c2[7];
char grid[5];
if (nc1 == NBASE+1) {
// CQ with standard callsign
unpackcall(nc2, c2);
unpackgrid(ng, grid);
strcpy(message, "CQ ");
strcat(message, c2);
strcat(message, " ");
strcat(message, grid);
return 0;
}
if (nc1 >= 267649090L && nc1 <= 267698374L) {
// CQ with suffix (e.g. /QRP)
uint32_t n = nc1 - 267649090L;
char sf[4];
sf[0] = charn(n % 37);
n /= 37;
sf[1] = charn(n % 37);
n /= 37;
sf[2] = charn(n % 37);
unpackcall(nc2, c2);
unpackgrid(ng, grid);
strcpy(message, "CQ ");
strcat(message, c2);
strcat(message, "/");
strcat(message, sf);
strcat(message, " ");
strcat(message, grid);
return 0;
}
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// Standard two-call exchange
char c1[7];
unpackcall(nc1, c1);
if (equals(c1, "CQ9DX ")) {
strcpy(c1, "CQ DX");
}
else if (starts_with(c1, " E9") && is_letter(c1[3]) && is_letter(c1[4]) && is_space(c1[5])) {
strcpy(c1, "CQ ");
c1[5] = 0;
}
unpackcall(nc2, c2);
unpackgrid(ng, grid);
strcpy(message, c1);
strcat(message, " ");
strcat(message, c2);
strcat(message, " ");
strcat(message, grid);
return 0;
}