CRC checksums (CRC-16, CRC-32, CRC-32C) for OCaml
CRC-32: use Int32 via C32 module for js_of_ocaml compatibility
Remove assert (Sys.int_size > 32) that crashes on 32-bit targets.
CRC-32 and CRC-32C now use a C32 submodule with Int32 arithmetic,
correct on both 64-bit native and js_of_ocaml. CRC-16 unchanged.
+45
-45
+45
-45
lib/crc.ml
+45
-45
lib/crc.ml
···
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(* Requires 64-bit OCaml: CRC-32 polynomials need >32 bits of native int. *)
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let () = assert (Sys.int_size > 32)
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-
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1
(* {1 CRC-16-CCITT}
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2
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3
Polynomial: x^16 + x^12 + x^5 + 1 (0x1021)
···
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done;
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!crc lxor 0xFFFF
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-
(* {1 CRC-32 (ISO 3309)}
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(* {1 CRC-32}
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+
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All CRC-32 variants use Int32 arithmetic so they work on both
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64-bit native OCaml and 32-bit targets (js_of_ocaml, wasm). *)
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module C32 = struct
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let ( lxor ) = Int32.logxor
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let ( land ) = Int32.logand
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let ( lsr ) = Int32.shift_right_logical
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+
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let make_table poly =
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Array.init 256 (fun i ->
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let crc = ref (Int32.of_int i) in
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for _ = 0 to 7 do
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if !crc land 1l <> 0l then crc := (!crc lsr 1) lxor poly
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else crc := !crc lsr 1
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done;
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!crc)
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+
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let compute table data =
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let crc = ref 0xFFFFFFFFl in
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for i = 0 to String.length data - 1 do
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let byte = Int32.of_int (Char.code (String.unsafe_get data i)) in
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let idx = Int32.to_int ((!crc lxor byte) land 0xFFl) in
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crc := table.(idx) lxor (!crc lsr 8)
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done;
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Int32.to_int (!crc lxor 0xFFFFFFFFl)
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let compute_bytes table buf off len =
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let crc = ref 0xFFFFFFFFl in
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for i = off to off + len - 1 do
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let byte = Int32.of_int (Char.code (Bytes.unsafe_get buf i)) in
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let idx = Int32.to_int ((!crc lxor byte) land 0xFFl) in
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crc := table.(idx) lxor (!crc lsr 8)
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done;
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Int32.to_int (!crc lxor 0xFFFFFFFFl)
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end
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(* {2 CRC-32 (ISO 3309)}
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Polynomial: 0xEDB88320 (reflected form of 0x04C11DB7)
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Init: 0xFFFFFFFF, XOR out: 0xFFFFFFFF. *)
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let crc32_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 0xEDB88320
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else crc := !crc lsr 1
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done;
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!crc)
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let crc32_table = C32.make_table 0xEDB88320l
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let crc32 data = C32.compute crc32_table data
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let crc32 data =
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let crc = ref 0xFFFFFFFF 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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crc := crc32_table.(!crc lxor byte land 0xFF) lxor (!crc lsr 8)
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done;
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!crc lxor 0xFFFFFFFF
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-
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-
(* {1 CRC-32C (Castagnoli)}
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(* {2 CRC-32C (Castagnoli)}
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Polynomial: 0x82F63B78 (reflected form of 0x1EDC6F41)
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Init: 0xFFFFFFFF, XOR out: 0xFFFFFFFF.
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Used by iSCSI, ext4, Btrfs. *)
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let crc32c_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 0x82F63B78
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else crc := !crc lsr 1
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done;
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!crc)
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let crc32c data =
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let crc = ref 0xFFFFFFFF 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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crc := crc32c_table.(!crc lxor byte land 0xFF) lxor (!crc lsr 8)
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done;
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!crc lxor 0xFFFFFFFF
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let crc32c_bytes buf off len =
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let crc = ref 0xFFFFFFFF in
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for i = off to off + len - 1 do
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let byte = Char.code (Bytes.unsafe_get buf i) in
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crc := crc32c_table.(!crc lxor byte land 0xFF) lxor (!crc lsr 8)
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done;
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!crc lxor 0xFFFFFFFF
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let crc32c_table = C32.make_table 0x82F63B78l
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let crc32c data = C32.compute crc32c_table data
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let crc32c_bytes buf off len = C32.compute_bytes crc32c_table buf off len