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bptc: rewrite; fixed encoder; added tests

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pull/1/head
Wijnand Modderman-Lenstra 9 years ago
parent 500a97e3f3
commit 599d42dca9
3 changed files with 389 additions and 37 deletions
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205
bptc/bptc.go
Unescape Escape View File

@ -2,71 +2,202 @@ package bptc
import (
"fmt"
"os"
"github.com/pd0mz/go-dmr"
"github.com/pd0mz/go-dmr/fec"
)
func Decode(info []byte, payload []byte) error {
var (
debug bool
// deinterleave matrix
dm = [256]uint8{}
)
func init() {
debug = os.Getenv("DEBUG_DMR_BPTC") != ""
var i uint32
for i = 0; i < 0x100; i++ {
dm[i] = uint8((i * 181) % 196)
}
}
func dump(bits []byte) {
for row := 0; row < 13; row++ {
if row == 0 {
fmt.Printf("col # ")
for col := 0; col < 15; col++ {
fmt.Printf("%02d ", col+1)
if col == 10 {
fmt.Print("| ")
}
}
fmt.Println("")
}
if row == 9 {
fmt.Println(" ------------------------------- ------------")
}
for col := 0; col < 15; col++ {
if col == 0 {
fmt.Printf("row #%02d: ", row+1)
}
fmt.Printf(" %d ", bits[col+row*15+1])
if col == 10 {
fmt.Print("| ")
}
}
fmt.Println("")
}
}
func Decode(info, data []byte) error {
if len(info) < 196 {
return fmt.Errorf("bptc: info size %d too small, need at least 196 bits", len(info))
}
if len(payload) < 12 {
return fmt.Errorf("bptc: payload size %d too small, need at least 12 bytes", len(payload))
if len(data) < 12 {
return fmt.Errorf("bptc: data size %d too small, need at least 12 bytes", len(data))
}
var (
i, j, k uint32
datafr = make([]byte, 196)
extracted = make([]byte, 96)
i, j, k uint32
bits = make([]byte, 196)
temp = make([]byte, 196)
)
// Deinterleave bits
// Deinterleave
for i = 1; i < 197; i++ {
datafr[i-1] = info[((i * 181) % 196)]
bits[i-1] = info[dm[i]]
}
// Zero reserved bits
for i = 0; i < 3; i++ {
datafr[0*15+i] = 0
if debug {
dump(bits)
}
for i = 0; i < 15; i++ {
var codeword uint32
for j = 0; j < 13; j++ {
codeword <<= 1
codeword |= uint32(datafr[j*15+i])
}
// Hamming checks
if err := hamming_check(bits); err != nil {
return err
}
fec.Hamming15_11_3_Correct(&codeword)
codeword &= 0x01ff
for j = 0; j < 9; j++ {
datafr[j*15+i] = byte((codeword >> (8 - j)) & 1)
// Extract data bits
for i, k = 3, 0; i < 11; i, k = i+1, k+1 {
temp[k] = bits[0*15+i]
}
for j = 1; j < 9; j++ {
for i = 0; i < 11; i, k = i+1, k+1 {
temp[k] = bits[j*15+i]
}
}
for j = 0; j < 9; j++ {
var codeword uint32
for i = 0; i < 15; i++ {
codeword <<= 1
codeword |= uint32(datafr[j*15+i])
copy(data, dmr.BitsToBytes(temp))
return nil
}
func Encode(data, info []byte) error {
if len(data) < 12 {
return fmt.Errorf("bptc: data size %d too small, need at least 12 bytes", len(data))
}
if len(info) < 196 {
return fmt.Errorf("bptc: info size %d too small, need at least 196 bits", len(info))
}
var (
bits = dmr.BytesToBits(data)
temp = make([]byte, 196)
errs = make([]byte, 4)
cols = make([]byte, 13)
)
var c, r, k uint32
for r = 0; r < 9; r++ {
if r == 0 {
for c = 3; c < 11; c, k = c+1, k+1 {
temp[c] = bits[k]
}
} else {
for c = 0; c < 11; c, k = c+1, k+1 {
temp[c+r*15] = bits[k]
}
}
fec.Hamming15_11_3_Correct(&codeword)
for i = 0; i < 11; i++ {
datafr[j*15+10-i] = byte((codeword >> i) & 1)
hamming_15_11_3_parity(temp[r*15:], errs)
temp[r*15+11] = errs[0]
temp[r*15+12] = errs[1]
temp[r*15+13] = errs[2]
temp[r*15+14] = errs[3]
}
for c = 0; c < 15; c++ {
for r = 0; r < 9; r++ {
cols[r] = temp[c+r*15+1]
}
hamming_13_9_3_parity(cols, errs)
temp[c+135+1] = errs[0]
temp[c+135+15+1] = errs[1]
temp[c+135+30+1] = errs[2]
temp[c+135+45+1] = errs[3]
}
// Extract data bits
for i, k = 3, 0; i < 11; i, k = i+1, k+1 {
extracted[k] = datafr[0*15+i]
if debug {
dump(temp)
}
for j = 1; j < 9; j++ {
for i = 0; i < 11; i, k = i+1, k+1 {
extracted[k] = datafr[j*15+i]
// Interleave
for k = 1; k < 197; k++ {
info[dm[k]] = temp[k-1]
}
return nil
}
// Hamming(13, 9, 3) check
func hamming_13_9_3_parity(bits, errs []byte) bool {
errs[0] = bits[0] ^ bits[1] ^ bits[3] ^ bits[5] ^ bits[6]
errs[1] = bits[0] ^ bits[1] ^ bits[2] ^ bits[4] ^ bits[6] ^ bits[7]
errs[2] = bits[0] ^ bits[1] ^ bits[2] ^ bits[3] ^ bits[5] ^ bits[7] ^ bits[8]
errs[3] = bits[0] ^ bits[2] ^ bits[4] ^ bits[5] ^ bits[8]
return (errs[0] == bits[9]) && (errs[1] == bits[10]) && (errs[2] == bits[11]) && (errs[3] == bits[12])
}
// Hamming(15, 11, 3) check
func hamming_15_11_3_parity(bits, errs []byte) bool {
errs[0] = bits[0] ^ bits[1] ^ bits[2] ^ bits[3] ^ bits[5] ^ bits[7] ^ bits[8]
errs[1] = bits[1] ^ bits[2] ^ bits[3] ^ bits[4] ^ bits[6] ^ bits[8] ^ bits[9]
errs[2] = bits[2] ^ bits[3] ^ bits[4] ^ bits[5] ^ bits[7] ^ bits[9] ^ bits[10]
errs[3] = bits[0] ^ bits[1] ^ bits[2] ^ bits[4] ^ bits[6] ^ bits[7] ^ bits[10]
return (errs[0] == bits[11]) && (errs[1] == bits[12]) && (errs[2] == bits[13]) && (errs[3] == bits[14])
}
// hamming_check checks each row with a Hamming(15,11,3) code and each column with Hamming(13, 9, 3)
func hamming_check(bits []byte) error {
var (
c, r, k uint32
row = make([]byte, 15)
col = make([]byte, 13)
errs = make([]byte, 4)
)
// Run through each of the 9 rows containing data
for r = 0; r < 9; r++ {
k = r*15 + 1
for a := 0; a < 15; a++ {
row[a] = bits[k]
}
if !hamming_15_11_3_parity(row, errs) {
return fmt.Errorf("hamming(15, 11, 3) check failed on row #%d", r)
}
}
copy(payload, dmr.BitsToBytes(extracted))
// Run through each of the 15 columns
for c = 0; c < 15; c++ {
k = c + 1
for a := 0; a < 13; a, k = a+1, k+15 {
col[a] = bits[k]
}
if !hamming_13_9_3_parity(col, errs) {
return fmt.Errorf("hamming(13, 9, 3) check failed on col #%d", c)
}
}
return nil
}

56
bptc/bptc_test.go
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@ -0,0 +1,56 @@
package bptc
import (
"bytes"
"encoding/hex"
"testing"
"github.com/pd0mz/go-dmr"
)
var (
encoded = []byte{
0x4b, 0xb2, 0x1d, 0x6d, 0x82, 0xd4,
0x23, 0x34, 0x0e, 0xe9, 0x66, 0xf3,
0xc2, 0x20, 0xc3, 0x87, 0xfd, 0x84,
0x54, 0x12, 0x4d, 0xb2, 0xd1, 0x40,
0x70,
}
decoded = []byte{
0xbd, 0x00, 0x80, 0x03, 0x1f, 0x29,
0x66, 0x1f, 0x2c, 0xa4, 0x66, 0x7e,
}
)
func TestDecode(t *testing.T) {
var want = dmr.BytesToBits(encoded)
var test = make([]byte, 12)
if err := Decode(want, test); err != nil {
t.Fatalf("decode failed: %v", err)
}
if !bytes.Equal(test, decoded) {
t.Fatalf("decode failed: not equal")
}
t.Logf("input:\n%s", hex.Dump(encoded))
t.Logf("decoded:\n%s", hex.Dump(test))
}
func TestEncode(t *testing.T) {
var want = make([]byte, 12)
var bits = make([]byte, 196)
copy(want, decoded)
if err := Encode(want, bits); err != nil {
t.Fatalf("encode failed: %v", err)
}
test := dmr.BitsToBytes(bits)
if !bytes.Equal(test, encoded) {
t.Fatalf("encode failed: not equal")
}
t.Logf("input:\n%s", hex.Dump(decoded))
t.Logf("encoded:\n%s", hex.Dump(test))
}

165
bptc/testdata/bptc.go vendored
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@ -0,0 +1,165 @@
package bptc
import (
"fmt"
"os"
"github.com/pd0mz/go-dmr"
"github.com/pd0mz/go-dmr/fec"
)
// deinterleave matrix
var dm = [256]uint8{}
var debug bool
func init() {
var i uint32
for i = 0; i < 0x100; i++ {
dm[i] = uint8((i * 181) % 196)
}
debug = os.Getenv("DEBUG_DMR_BPTC") != ""
}
func dump(bits []byte) {
for row := 0; row < 13; row++ {
if row == 0 {
fmt.Printf("col # ")
for col := 0; col < 15; col++ {
fmt.Printf("%02d ", col+1)
if col == 10 {
fmt.Print("| ")
}
}
fmt.Println("")
}
if row == 9 {
fmt.Println(" ------------------------------- ------------")
}
for col := 0; col < 15; col++ {
if col == 0 {
fmt.Printf("row #%02d: ", row+1)
}
fmt.Printf(" %d ", bits[col+row*15+1])
if col == 10 {
fmt.Print("| ")
}
}
fmt.Println("")
}
}
func Decode(info, data []byte) error {
if len(info) < 196 {
return fmt.Errorf("bptc: info size %d too small, need at least 196 bits", len(info))
}
if len(data) < 12 {
return fmt.Errorf("bptc: data size %d too small, need at least 12 bytes", len(data))
}
var (
i, j, k uint32
datafr = make([]byte, 196)
extracted = make([]byte, 96)
)
// Deinterleave bits
for i = 1; i < 197; i++ {
datafr[i-1] = info[dm[i]]
}
if debug {
dump(datafr)
}
// Zero reserved bits
for i = 0; i < 3; i++ {
datafr[0*15+i] = 0
}
for i = 0; i < 15; i++ {
var codeword uint32
for j = 0; j < 13; j++ {
codeword <<= 1
codeword |= uint32(datafr[j*15+i])
}
fec.Hamming15_11_3_Correct(&codeword)
codeword &= 0x01ff
for j = 0; j < 9; j++ {
datafr[j*15+i] = byte((codeword >> (8 - j)) & 1)
}
}
for j = 0; j < 9; j++ {
var codeword uint32
for i = 0; i < 15; i++ {
codeword <<= 1
codeword |= uint32(datafr[j*15+i])
}
fec.Hamming15_11_3_Correct(&codeword)
for i = 0; i < 11; i++ {
datafr[j*15+10-i] = byte((codeword >> i) & 1)
}
}
// Extract data bits
for i, k = 3, 0; i < 11; i, k = i+1, k+1 {
extracted[k] = datafr[0*15+i]
}
for j = 1; j < 9; j++ {
for i = 0; i < 11; i, k = i+1, k+1 {
extracted[k] = datafr[j*15+i]
}
}
copy(data, dmr.BitsToBytes(extracted))
return nil
}
func Encode(data, info []byte) error {
if len(data) < 12 {
return fmt.Errorf("bptc: data size %d too small, need at least 12 bytes", len(data))
}
if len(info) < 196 {
return fmt.Errorf("bptc: info size %d too small, need at least 196 bits", len(info))
}
var (
i, j, k uint32
datafr = make([]byte, 196)
extracted = make([]byte, 96)
)
copy(extracted, dmr.BytesToBits(data))
for i = 0; i < 9; i++ {
if i == 0 {
for j = 3; j < 11; j++ {
datafr[j+1] = extracted[k]
k++
}
} else {
for j = 0; j < 11; j++ {
datafr[j+i*15+1] = extracted[k]
k++
}
}
datafr[i*15+11+1] = 8
datafr[i*15+12+1] = 8
datafr[i*15+13+1] = 8
datafr[i*15+14+1] = 8
}
// Interleave bits
for i = 1; i < 197; i++ {
info[dm[i]] = datafr[i-1]
}
if debug {
dump(info)
}
return nil
}
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