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31 lines
1.3 KiB
31 lines
1.3 KiB
package brotli
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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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/* 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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func prefixEncodeCopyDistance(distance_code uint, num_direct_codes uint, postfix_bits uint, code *uint16, extra_bits *uint32) {
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if distance_code < numDistanceShortCodes+num_direct_codes {
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*code = uint16(distance_code)
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*extra_bits = 0
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return
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} else {
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var dist uint = (uint(1) << (postfix_bits + 2)) + (distance_code - numDistanceShortCodes - num_direct_codes)
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var bucket uint = uint(log2FloorNonZero(dist) - 1)
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var postfix_mask uint = (1 << postfix_bits) - 1
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var postfix uint = dist & postfix_mask
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var prefix uint = (dist >> bucket) & 1
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var offset uint = (2 + prefix) << bucket
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var nbits uint = bucket - postfix_bits
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*code = uint16(nbits<<10 | (numDistanceShortCodes + num_direct_codes + ((2*(nbits-1) + prefix) << postfix_bits) + postfix))
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*extra_bits = uint32((dist - offset) >> postfix_bits)
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}
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}
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