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54 lines
2 KiB
C
54 lines
2 KiB
C
/*
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* Copyright 2024 Google LLC
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#pragma once
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#include <stdint.h>
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#include <string.h>
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//! \file
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//! Calculate the legacy checksum of data.
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//!
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//! The calculation is somewhat like a CRC with the CRC-32 polynomial, but with
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//! the data bytes reordered oddly. The checksum is calculated 32 bits at a
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//! time, little-endian, MSB-first. The legacy checksum of bytes A B C D E F G H
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//! is equal to the CRC-32 of bytes D C B A H G F E (xor 0xFFFFFFFF). When the
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//! data being checksummmed is not a multiple of four bytes in length, the
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//! remainder bytes are zero-padded and byte-swapped(!) before being checksummed
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//! like the previous full words. For example, the legacy checksum of bytes
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//! 1 2 3 4 5 6 is equal to the checksum of bytes 1 2 3 4 6 5 0 0, which is
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//! equivalent to the CRC-32 of bytes 4 3 2 1 0 0 5 6 (xor 0xFFFFFFFF).
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//!
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//! The legacy checksum should not be used except when required for
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//! backwards-compatibility purposes.
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typedef struct LegacyChecksum {
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uint32_t reg;
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uint8_t accumulator[3];
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uint8_t accumulated_length;
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} LegacyChecksum;
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void legacy_defective_checksum_init(LegacyChecksum *checksum);
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void legacy_defective_checksum_update(
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LegacyChecksum * restrict checksum,
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const void * restrict data, size_t length);
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uint32_t legacy_defective_checksum_finish(LegacyChecksum *checksum);
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//! Convenience wrapper to checksum memory in one shot.
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uint32_t legacy_defective_checksum_memory(const void * restrict data,
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size_t length);
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