CRC checksums (CRC-16, CRC-32, CRC-32C) for OCaml
Strengthen CRC tests: residue, boundary, hw/sw agreement
- Add CRC-32C single byte "A" test (0xE16DCDEE, RevEng catalogue)
- Add CRC-32 and CRC-32C residue tests: verify that CRC(data || LE(CRC))
yields the expected constant (residue XOR xorout per RevEng)
- Add slicing-by-8 boundary tests at 1,7,8,9,15,16,17,31-65 bytes
to stress the 8-byte bulk loop and tail
- Add fuzz tests for hardware vs software agreement on CRC-32 and CRC-32C
+58
+10
fuzz/fuzz_crc.ml
+10
fuzz/fuzz_crc.ml
···
61
61
let test_crc32c_deterministic s =
62
62
check_eq ~pp:Format.pp_print_int (Crc.crc32c s) (Crc.crc32c s)
63
63
64
+
(* CRC-32: hardware and software agree *)
65
+
let test_crc32_hw_sw_agree s =
66
+
check_eq ~pp:Format.pp_print_int (Crc.crc32 s) (Crc.crc32_software s)
67
+
68
+
(* CRC-32C: hardware and software agree *)
69
+
let test_crc32c_hw_sw_agree s =
70
+
check_eq ~pp:Format.pp_print_int (Crc.crc32c s) (Crc.crc32c_software s)
71
+
64
72
let suite =
65
73
( "crc",
66
74
[
···
73
81
test_case "32-bit range (crc32c)" [ bytes ] test_crc32c_32bit;
74
82
test_case "deterministic (ccitt)" [ bytes ] test_ccitt_deterministic;
75
83
test_case "deterministic (crc32c)" [ bytes ] test_crc32c_deterministic;
84
+
test_case "hw=sw (crc32)" [ bytes ] test_crc32_hw_sw_agree;
85
+
test_case "hw=sw (crc32c)" [ bytes ] test_crc32c_hw_sw_agree;
76
86
] )
+48
test/test_crc.ml
+48
test/test_crc.ml
···
84
84
check "RFC 3720 check value" 0xE3069283 (Crc.crc32c check_string)
85
85
86
86
let test_crc32c_empty () = check "empty input" 0 (Crc.crc32c "")
87
+
let test_crc32c_single () = check "single byte 0x41" 0xE16DCDEE (Crc.crc32c "A")
87
88
88
89
let test_crc32c_bytes () =
89
90
let buf = Bytes.of_string ("xx" ^ check_string ^ "zz") in
···
111
112
let data = String.init 32 (fun i -> Char.chr (31 - i)) in
112
113
check "RFC 3720: descending bytes" 0x113FDB5C (Crc.crc32c data)
113
114
115
+
(* {1 CRC-32 residue test}
116
+
117
+
For reflected CRC, appending the CRC little-endian yields a constant.
118
+
RevEng catalogue: CRC-32/ISO-HDLC residue=0xdebb20e3 (pre-XOR).
119
+
Our function applies xorout=0xFFFFFFFF, so the observed constant is
120
+
residue XOR xorout = 0xDEBB20E3 XOR 0xFFFFFFFF = 0x2144DF1C. *)
121
+
122
+
let test_crc32_residue () =
123
+
let data = "Hello, CRC!" in
124
+
let crc = Crc.crc32 data in
125
+
let with_crc =
126
+
data ^ String.init 4 (fun i -> Char.chr ((crc lsr (i * 8)) land 0xFF))
127
+
in
128
+
check "CRC-32 residue" 0x2144DF1C (Crc.crc32 with_crc)
129
+
130
+
(* {1 CRC-32C residue test}
131
+
132
+
RevEng catalogue: CRC-32/ISCSI residue=0xb798b438 (pre-XOR).
133
+
Observed: 0xB798B438 XOR 0xFFFFFFFF = 0x48674BC7. *)
134
+
135
+
let test_crc32c_residue () =
136
+
let data = "Hello, CRC!" in
137
+
let crc = Crc.crc32c data in
138
+
let with_crc =
139
+
data ^ String.init 4 (fun i -> Char.chr ((crc lsr (i * 8)) land 0xFF))
140
+
in
141
+
check "CRC-32C residue" 0x48674BC7 (Crc.crc32c with_crc)
142
+
143
+
(* {1 Slicing-by-8 boundary tests}
144
+
145
+
The slicing-by-8 loop processes 8 bytes per iteration. These tests
146
+
exercise lengths at and around the 8-byte boundary to stress the
147
+
transition between the bulk loop and the byte-at-a-time tail. *)
148
+
149
+
let test_crc32c_boundary () =
150
+
let check_len n =
151
+
let data = String.init n (fun i -> Char.chr (i land 0xFF)) in
152
+
let hw = Crc.crc32c data in
153
+
let sw = Crc.crc32c_software data in
154
+
check (Printf.sprintf "%d bytes: hw=sw" n) sw hw
155
+
in
156
+
List.iter check_len [ 1; 7; 8; 9; 15; 16; 17; 31; 32; 33; 63; 64; 65 ]
157
+
114
158
let suite =
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159
( "crc",
116
160
[
···
128
172
Alcotest.test_case "crc32: single byte" `Quick test_crc32_single;
129
173
Alcotest.test_case "crc32c: RFC 3720 check" `Quick test_crc32c_check;
130
174
Alcotest.test_case "crc32c: empty" `Quick test_crc32c_empty;
175
+
Alcotest.test_case "crc32c: single byte" `Quick test_crc32c_single;
131
176
Alcotest.test_case "crc32c: bytes sub-range" `Quick test_crc32c_bytes;
132
177
Alcotest.test_case "crc32c: RFC 3720: 32 zeros" `Quick
133
178
test_crc32c_rfc3720_zeros;
···
137
182
test_crc32c_rfc3720_ascending;
138
183
Alcotest.test_case "crc32c: RFC 3720: descending" `Quick
139
184
test_crc32c_rfc3720_descending;
185
+
Alcotest.test_case "crc32: residue" `Quick test_crc32_residue;
186
+
Alcotest.test_case "crc32c: residue" `Quick test_crc32c_residue;
187
+
Alcotest.test_case "crc32c: slicing boundary" `Quick test_crc32c_boundary;
140
188
] )