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hdlc_decoder: move address_length_ and crc16_x25_check_ outside of the class to a cpp file
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Lines changed: 60 additions & 73 deletions

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‎src/dlms_parser/hdlc_decoder.cpp‎

Lines changed: 60 additions & 29 deletions
Original file line numberDiff line numberDiff line change
@@ -4,6 +4,61 @@
44

55
namespace dlms_parser {
66

7+
// Precomputed CRC-16/IBM-SDLC (X.25) Lookup Table
8+
constexpr uint16_t CRC16_X25_TABLE[256] = {
9+
0x0000, 0x1189, 0x2312, 0x329b, 0x4624, 0x57ad, 0x6536, 0x74bf,
10+
0x8c48, 0x9dc1, 0xaf5a, 0xbed3, 0xca6c, 0xdbe5, 0xe97e, 0xf8f7,
11+
0x1081, 0x0108, 0x3393, 0x221a, 0x56a5, 0x472c, 0x75b7, 0x643e,
12+
0x9cc9, 0x8d40, 0xbfdb, 0xae52, 0xdaed, 0xcb64, 0xf9ff, 0xe876,
13+
0x2102, 0x308b, 0x0210, 0x1399, 0x6726, 0x76af, 0x4434, 0x55bd,
14+
0xad4a, 0xbcc3, 0x8e58, 0x9fd1, 0xeb6e, 0xfae7, 0xc87c, 0xd9f5,
15+
0x3183, 0x200a, 0x1291, 0x0318, 0x77a7, 0x662e, 0x54b5, 0x453c,
16+
0xbdcb, 0xac42, 0x9ed9, 0x8f50, 0xfbef, 0xea66, 0xd8fd, 0xc974,
17+
0x4204, 0x538d, 0x6116, 0x709f, 0x0420, 0x15a9, 0x2732, 0x36bb,
18+
0xce4c, 0xdfc5, 0xed5e, 0xfcd7, 0x8868, 0x99e1, 0xab7a, 0xbaf3,
19+
0x5285, 0x430c, 0x7197, 0x601e, 0x14a1, 0x0528, 0x37b3, 0x263a,
20+
0xdecd, 0xcf44, 0xfddf, 0xec56, 0x98e9, 0x8960, 0xbbfb, 0xaa72,
21+
0x6306, 0x728f, 0x4014, 0x519d, 0x2522, 0x34ab, 0x0630, 0x17b9,
22+
0xef4e, 0xfec7, 0xcc5c, 0xddd5, 0xa96a, 0xb8e3, 0x8a78, 0x9bf1,
23+
0x7387, 0x620e, 0x5095, 0x411c, 0x35a3, 0x242a, 0x16b1, 0x0738,
24+
0xffcf, 0xee46, 0xdcdd, 0xcd54, 0xb9eb, 0xa862, 0x9af9, 0x8b70,
25+
0x8408, 0x9581, 0xa71a, 0xb693, 0xc22c, 0xd3a5, 0xe13e, 0xf0b7,
26+
0x0840, 0x19c9, 0x2b52, 0x3adb, 0x4e64, 0x5fed, 0x6d76, 0x7cff,
27+
0x9489, 0x8500, 0xb79b, 0xa612, 0xd2ad, 0xc324, 0xf1bf, 0xe036,
28+
0x18c1, 0x0948, 0x3bd3, 0x2a5a, 0x5ee5, 0x4f6c, 0x7df7, 0x6c7e,
29+
0xa50a, 0xb483, 0x8618, 0x9791, 0xe32e, 0xf2a7, 0xc03c, 0xd1b5,
30+
0x2942, 0x38cb, 0x0a50, 0x1bd9, 0x6f66, 0x7eef, 0x4c74, 0x5dfd,
31+
0xb58b, 0xa402, 0x9699, 0x8710, 0xf3af, 0xe226, 0xd0bd, 0xc134,
32+
0x39c3, 0x284a, 0x1ad1, 0x0b58, 0x7fe7, 0x6e6e, 0x5cf5, 0x4d7c,
33+
0xc60c, 0xd785, 0xe51e, 0xf497, 0x8028, 0x91a1, 0xa33a, 0xb2b3,
34+
0x4a44, 0x5bcd, 0x6956, 0x78df, 0x0c60, 0x1de9, 0x2f72, 0x3efb,
35+
0xd68d, 0xc704, 0xf59f, 0xe416, 0x90a9, 0x8120, 0xb3bb, 0xa232,
36+
0x5ac5, 0x4b4c, 0x79d7, 0x685e, 0x1ce1, 0x0d68, 0x3ff3, 0x2e7a,
37+
0xe70e, 0xf687, 0xc41c, 0xd595, 0xa12a, 0xb0a3, 0x8238, 0x93b1,
38+
0x6b46, 0x7acf, 0x4854, 0x59dd, 0x2d62, 0x3ceb, 0x0e70, 0x1ff9,
39+
0xf78f, 0xe606, 0xd49d, 0xc514, 0xb1ab, 0xa022, 0x92b9, 0x8330,
40+
0x7bc7, 0x6a4e, 0x58d5, 0x495c, 0x3de3, 0x2c6a, 0x1ef1, 0x0f78 };
41+
42+
// CRC-16/IBM-SDLC (X.25): poly=0x8408, init=0xFFFF, xorout=0xFFFF.
43+
// Running this over (data bytes + the two stored CRC bytes) yields FCS16_GOOD_VALUE for a valid frame.
44+
bool crc16_x25_check(const std::span<const uint8_t> data) {
45+
uint16_t crc = 0xFFFFU;
46+
for (const auto byte : data) {
47+
crc = crc >> 8 ^ CRC16_X25_TABLE[(crc ^ byte) & 0xFF];
48+
}
49+
return crc == 0xF0B8U;
50+
}
51+
52+
// Returns the number of bytes in a variable-length HDLC address field (1, 2 or 4).
53+
// Returns 0 if the terminating LSB=1 bit is not found within 4 bytes.
54+
static size_t address_length(std::span<const uint8_t> p) {
55+
const auto limit = std::min(p.size(), size_t{ 4 });
56+
for (size_t i = 0; i < limit; ++i) {
57+
if (p[i] & 0x01U) return i + 1; // LSB=1 marks the last address byte
58+
}
59+
return 0;
60+
}
61+
762
static constexpr uint8_t HDLC_FLAG = 0x7E;
863
// static constexpr uint8_t HDLC_ESCAPE = 0x7D; // byte-stuffing disabled, see decode_one_()
964
// static constexpr uint8_t HDLC_ESCAPE_XOR = 0x20;
@@ -41,30 +96,6 @@ FrameStatus HdlcDecoder::check(const std::span<const uint8_t> buf) {
4196
return FrameStatus::NEED_MORE;
4297
}
4398

44-
// After running crc16_x25_check_ over a data region AND then over the two stored CRC
45-
// bytes, the result must equal this constant (from RFC 1662 / hdlcpp).
46-
static constexpr uint16_t FCS16_GOOD_VALUE = 0xF0B8U;
47-
48-
size_t HdlcDecoder::address_length_(const std::span<const uint8_t> p) {
49-
const auto limit = std::min(p.size(), size_t{4});
50-
for (size_t i = 0; i < limit; ++i) {
51-
if (p[i] & 0x01U) return i + 1; // LSB=1 marks the last address byte
52-
}
53-
return 0;
54-
}
55-
56-
// CRC-16/IBM-SDLC (X.25): poly=0x8408, init=0xFFFF, xorout=0xFFFF.
57-
// Running this over (data bytes + the two stored CRC bytes) yields FCS16_GOOD_VALUE for a valid frame.
58-
uint16_t HdlcDecoder::crc16_x25_check_(const std::span<const uint8_t> data) {
59-
uint16_t crc = 0xFFFFU;
60-
for (const auto byte : data) {
61-
crc = crc >> 8 ^ CRC16_X25_TABLE[(crc ^ byte) & 0xFF];
62-
}
63-
// Return raw register value (no xor-out) for "good value" verification:
64-
// when CRC is run over (data + stored_FCS), the raw register equals FCS16_GOOD_VALUE.
65-
return crc;
66-
}
67-
6899
// ---------------------------------------------------------------------------
69100
// In-place decode: extracts and concatenates payloads from all HDLC frames
70101
// in buf, writing them sequentially to buf[0..]. Returns new length, 0 on error.
@@ -100,25 +131,25 @@ size_t HdlcDecoder::decode(const std::span<uint8_t> buf_span) const {
100131

101132
// Skip addresses + control
102133
size_t pos = 2;
103-
const auto dst_len = address_length_(inner.subspan(pos));
134+
const auto dst_len = address_length(inner.subspan(pos));
104135
if (dst_len == 0) return 0;
105136
pos += dst_len;
106137

107-
const auto src_len = address_length_(inner.subspan(pos));
138+
const auto src_len = address_length(inner.subspan(pos));
108139
if (src_len == 0) return 0;
109140
pos += src_len;
110141
pos += 1; // control byte
111142

112143
// HCS
113144
if (pos + 2 > inner.size()) return 0;
114-
if (!skip_crc_check_ && crc16_x25_check_(inner.first(pos + 2)) != FCS16_GOOD_VALUE) {
145+
if (!skip_crc_check_ && !crc16_x25_check(inner.first(pos + 2))) {
115146
Logger::log(LogLevel::WARNING, "HDLC: HCS error");
116147
return 0;
117148
}
118149
pos += 2;
119150

120151
// FCS
121-
if (!skip_crc_check_ && crc16_x25_check_(inner) != FCS16_GOOD_VALUE) {
152+
if (!skip_crc_check_ && !crc16_x25_check(inner)) {
122153
Logger::log(LogLevel::WARNING, "HDLC: FCS error");
123154
return 0;
124155
}
@@ -151,4 +182,4 @@ size_t HdlcDecoder::decode(const std::span<uint8_t> buf_span) const {
151182
return write_offset;
152183
}
153184

154-
} // namespace dlms_parser
185+
}

‎src/dlms_parser/hdlc_decoder.h‎

Lines changed: 0 additions & 44 deletions
Original file line numberDiff line numberDiff line change
@@ -7,42 +7,6 @@
77

88
namespace dlms_parser {
99

10-
// Precomputed CRC-16/IBM-SDLC (X.25) Lookup Table
11-
inline constexpr uint16_t CRC16_X25_TABLE[256] = {
12-
0x0000, 0x1189, 0x2312, 0x329b, 0x4624, 0x57ad, 0x6536, 0x74bf,
13-
0x8c48, 0x9dc1, 0xaf5a, 0xbed3, 0xca6c, 0xdbe5, 0xe97e, 0xf8f7,
14-
0x1081, 0x0108, 0x3393, 0x221a, 0x56a5, 0x472c, 0x75b7, 0x643e,
15-
0x9cc9, 0x8d40, 0xbfdb, 0xae52, 0xdaed, 0xcb64, 0xf9ff, 0xe876,
16-
0x2102, 0x308b, 0x0210, 0x1399, 0x6726, 0x76af, 0x4434, 0x55bd,
17-
0xad4a, 0xbcc3, 0x8e58, 0x9fd1, 0xeb6e, 0xfae7, 0xc87c, 0xd9f5,
18-
0x3183, 0x200a, 0x1291, 0x0318, 0x77a7, 0x662e, 0x54b5, 0x453c,
19-
0xbdcb, 0xac42, 0x9ed9, 0x8f50, 0xfbef, 0xea66, 0xd8fd, 0xc974,
20-
0x4204, 0x538d, 0x6116, 0x709f, 0x0420, 0x15a9, 0x2732, 0x36bb,
21-
0xce4c, 0xdfc5, 0xed5e, 0xfcd7, 0x8868, 0x99e1, 0xab7a, 0xbaf3,
22-
0x5285, 0x430c, 0x7197, 0x601e, 0x14a1, 0x0528, 0x37b3, 0x263a,
23-
0xdecd, 0xcf44, 0xfddf, 0xec56, 0x98e9, 0x8960, 0xbbfb, 0xaa72,
24-
0x6306, 0x728f, 0x4014, 0x519d, 0x2522, 0x34ab, 0x0630, 0x17b9,
25-
0xef4e, 0xfec7, 0xcc5c, 0xddd5, 0xa96a, 0xb8e3, 0x8a78, 0x9bf1,
26-
0x7387, 0x620e, 0x5095, 0x411c, 0x35a3, 0x242a, 0x16b1, 0x0738,
27-
0xffcf, 0xee46, 0xdcdd, 0xcd54, 0xb9eb, 0xa862, 0x9af9, 0x8b70,
28-
0x8408, 0x9581, 0xa71a, 0xb693, 0xc22c, 0xd3a5, 0xe13e, 0xf0b7,
29-
0x0840, 0x19c9, 0x2b52, 0x3adb, 0x4e64, 0x5fed, 0x6d76, 0x7cff,
30-
0x9489, 0x8500, 0xb79b, 0xa612, 0xd2ad, 0xc324, 0xf1bf, 0xe036,
31-
0x18c1, 0x0948, 0x3bd3, 0x2a5a, 0x5ee5, 0x4f6c, 0x7df7, 0x6c7e,
32-
0xa50a, 0xb483, 0x8618, 0x9791, 0xe32e, 0xf2a7, 0xc03c, 0xd1b5,
33-
0x2942, 0x38cb, 0x0a50, 0x1bd9, 0x6f66, 0x7eef, 0x4c74, 0x5dfd,
34-
0xb58b, 0xa402, 0x9699, 0x8710, 0xf3af, 0xe226, 0xd0bd, 0xc134,
35-
0x39c3, 0x284a, 0x1ad1, 0x0b58, 0x7fe7, 0x6e6e, 0x5cf5, 0x4d7c,
36-
0xc60c, 0xd785, 0xe51e, 0xf497, 0x8028, 0x91a1, 0xa33a, 0xb2b3,
37-
0x4a44, 0x5bcd, 0x6956, 0x78df, 0x0c60, 0x1de9, 0x2f72, 0x3efb,
38-
0xd68d, 0xc704, 0xf59f, 0xe416, 0x90a9, 0x8120, 0xb3bb, 0xa232,
39-
0x5ac5, 0x4b4c, 0x79d7, 0x685e, 0x1ce1, 0x0d68, 0x3ff3, 0x2e7a,
40-
0xe70e, 0xf687, 0xc41c, 0xd595, 0xa12a, 0xb0a3, 0x8238, 0x93b1,
41-
0x6b46, 0x7acf, 0x4854, 0x59dd, 0x2d62, 0x3ceb, 0x0e70, 0x1ff9,
42-
0xf78f, 0xe606, 0xd49d, 0xc514, 0xb1ab, 0xa022, 0x92b9, 0x8330,
43-
0x7bc7, 0x6a4e, 0x58d5, 0x495c, 0x3de3, 0x2c6a, 0x1ef1, 0x0f78
44-
};
45-
4610
// Decodes a single complete HDLC frame as used in DLMS/COSEM push-mode telegrams.
4711
//
4812
// Frame layout:
@@ -65,14 +29,6 @@ class HdlcDecoder final : NonCopyableAndNonMovable {
6529

6630
private:
6731
bool skip_crc_check_{false};
68-
69-
// Returns the number of bytes in a variable-length HDLC address field (1, 2 or 4).
70-
// Returns 0 if the terminating LSB=1 bit is not found within 4 bytes.
71-
static size_t address_length_(std::span<const uint8_t> p);
72-
73-
// CRC16/IBM-SDLC (X.25) run over `len` bytes.
74-
// When called over (data + stored_fcs_bytes), returns 0xF0B8 for a valid frame.
75-
static uint16_t crc16_x25_check_(std::span<const uint8_t> data);
7632
};
7733

7834
} // namespace dlms_parser

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