CRC checksums (CRC-16, CRC-32, CRC-32C) for OCaml
Split ocaml-transport into ocaml-cltu and ocaml-cop1
- ocaml-cltu: CLTU encoding/decoding (CCSDS 231.0-B) with BCH(63,56),
ASM sync markers (131.0-B), and stream sync parsers
- ocaml-cop1: COP-1 state machines (CCSDS 232.1-B) for FOP-1 (ground)
and FARM-1 (flight) with Eio service layer
- cltu-eio: CLTU/ASM send/recv over Eio flows
- cop1-eio: COP-1 service layer with Eio timer management
+12
-8
+12
-8
lib/crc.ml
+12
-8
lib/crc.ml
···
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34
(* {1 CRC-16-X.25}
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Polynomial: 0x8408 (reflected form of 0x1021)
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-
Init: 0xFFFF, reflected in/out, XOR out: 0xFFFF.
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-
Bit-at-a-time reflected algorithm (fast enough for small frames). *)
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+
Init: 0xFFFF, reflected in/out, XOR out: 0xFFFF. *)
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+
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+
let crc16_x25_table =
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+
Array.init 256 (fun i ->
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+
let crc = ref i in
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+
for _ = 0 to 7 do
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+
if !crc land 1 <> 0 then crc := (!crc lsr 1) lxor 0x8408
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+
else crc := !crc lsr 1
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+
done;
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+
!crc)
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let crc16_x25 data =
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let crc = ref 0xFFFF in
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for i = 0 to String.length data - 1 do
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let byte = Char.code (String.unsafe_get data i) in
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-
for j = 0 to 7 do
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-
let bit = (byte lsr j) land 1 in
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-
let c0 = !crc land 1 in
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-
crc := !crc lsr 1;
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-
if bit lxor c0 = 1 then crc := !crc lxor 0x8408
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-
done
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+
let idx = !crc lxor byte land 0xFF in
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+
crc := (!crc lsr 8) lxor crc16_x25_table.(idx)
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done;
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!crc lxor 0xFFFF
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