55 lines
1.9 KiB
C
55 lines
1.9 KiB
C
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/* Copyright 2013 Google Inc. All Rights Reserved.
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Distributed under MIT license.
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See file LICENSE for detail or copy at https://opensource.org/licenses/MIT
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*/
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/* Functions for encoding of integers into prefix codes the amount of extra
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bits, and the actual values of the extra bits. */
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#ifndef BROTLI_ENC_PREFIX_H_
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#define BROTLI_ENC_PREFIX_H_
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#include "../common/constants.h"
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#include <brotli/port.h>
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#include <brotli/types.h>
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#include "./fast_log.h"
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#if defined(__cplusplus) || defined(c_plusplus)
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extern "C" {
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#endif
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/* Here distance_code is an intermediate code, i.e. one of the special codes or
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the actual distance increased by BROTLI_NUM_DISTANCE_SHORT_CODES - 1. */
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static BROTLI_INLINE void PrefixEncodeCopyDistance(size_t distance_code,
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size_t num_direct_codes,
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size_t postfix_bits,
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uint16_t* code,
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uint32_t* extra_bits) {
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if (distance_code < BROTLI_NUM_DISTANCE_SHORT_CODES + num_direct_codes) {
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*code = (uint16_t)distance_code;
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*extra_bits = 0;
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return;
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} else {
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size_t dist = ((size_t)1 << (postfix_bits + 2u)) +
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(distance_code - BROTLI_NUM_DISTANCE_SHORT_CODES - num_direct_codes);
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size_t bucket = Log2FloorNonZero(dist) - 1;
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size_t postfix_mask = (1u << postfix_bits) - 1;
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size_t postfix = dist & postfix_mask;
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size_t prefix = (dist >> bucket) & 1;
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size_t offset = (2 + prefix) << bucket;
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size_t nbits = bucket - postfix_bits;
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*code = (uint16_t)(
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(BROTLI_NUM_DISTANCE_SHORT_CODES + num_direct_codes +
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((2 * (nbits - 1) + prefix) << postfix_bits) + postfix));
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*extra_bits = (uint32_t)(
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(nbits << 24) | ((dist - offset) >> postfix_bits));
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}
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}
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#if defined(__cplusplus) || defined(c_plusplus)
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} /* extern "C" */
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#endif
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#endif /* BROTLI_ENC_PREFIX_H_ */
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