forked from madler/zlib
/
inffast_chunk.h
64 lines (57 loc) · 2.67 KB
/
inffast_chunk.h
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/* inffast_chunk.h -- header to use inffast_chunk.c
*
* (C) 1995-2013 Jean-loup Gailly and Mark Adler
*
* This software is provided 'as-is', without any express or implied
* warranty. In no event will the authors be held liable for any damages
* arising from the use of this software.
*
* Permission is granted to anyone to use this software for any purpose,
* including commercial applications, and to alter it and redistribute it
* freely, subject to the following restrictions:
*
* 1. The origin of this software must not be misrepresented; you must not
* claim that you wrote the original software. If you use this software
* in a product, an acknowledgment in the product documentation would be
* appreciated but is not required.
* 2. Altered source versions must be plainly marked as such, and must not be
* misrepresented as being the original software.
* 3. This notice may not be removed or altered from any source distribution.
*
* Jean-loup Gailly Mark Adler
* jloup@gzip.org madler@alumni.caltech.edu
*
* Copyright (C) 1995-2003, 2010 Mark Adler
* Copyright (C) 2017 ARM, Inc.
* Copyright 2023 The Chromium Authors
* For conditions of distribution and use, see copyright notice in zlib.h
*/
/* WARNING: this file should *not* be used by applications. It is
part of the implementation of the compression library and is
subject to change. Applications should only use zlib.h.
*/
#include "inffast.h"
/* INFLATE_FAST_MIN_INPUT:
The minimum number of input bytes needed so that we can safely call
inflate_fast() with only one up-front bounds check. One
length/distance code pair (15 bits for the length code, 5 bits for length
extra, 15 bits for the distance code, 13 bits for distance extra) requires
reading up to 48 input bits. Additionally, in the same iteraction, we may
decode two literals from the root-table (requiring MIN_OUTPUT = 258 + 2).
Each root-table entry is up to 10 bits, for a total of 68 input bits each
iteraction.
The refill variant reads 8 bytes from the buffer at a time, and advances
the input pointer by up to 7 bytes, ensuring there are at least 56-bits
available in the bit-buffer. The technique was documented by Fabian Giesen
on his blog as variant 4 in the article 'Reading bits in far too many ways':
https://fgiesen.wordpress.com/2018/02/20/
In the worst case, we may refill twice in the same iteraction, requiring
MIN_INPUT = 8 + 7.
*/
#ifdef INFLATE_CHUNK_READ_64LE
#undef INFLATE_FAST_MIN_INPUT
#define INFLATE_FAST_MIN_INPUT 15
#undef INFLATE_FAST_MIN_OUTPUT
#define INFLATE_FAST_MIN_OUTPUT 260
#endif
void ZLIB_INTERNAL inflate_fast_chunk_(z_streamp strm, unsigned start);