/* SPDX-License-Identifier: GPL-2.0-only */ /* * Copyright (C) 2024-2026, SUSE LLC * * Authors: Enzo Matsumiya <ematsumiya@suse.de> * * Implementation of the LZ77 "plain" compression algorithm, as per MS-XCA spec. */ #ifndef _SMB_COMPRESS_LZ77_H #define _SMB_COMPRESS_LZ77_H #include <linux/kernel.h> /** * lz77_compressed_alloc_size() - Compute compressed buffer size. * @size: uncompressed (src) size * * Compute allocation size for the compressed buffer based on uncompressed size. * Accounts for metadata and overprovision for the worst case scenario. * * LZ77 metadata is a 4-byte flag that is written: * - on dst begin (pos 0) * - every 32 literals or matches * - on end-of-stream (possibly, if last write was another flag) * * Worst case scenario is an all-literal compression, which means: * metadata bytes = 4 + ((@size / 32) * 4) + 4, or, simplified, (@size >> 3) + 8 * * The worst case scenario rarely happens, but such overprovisioning also allows lz77_compress() * main loop to run without ever bound checking dst, which is a huge perf improvement, while also * being safe when compression goes bad. * * Return: required (*) allocation size for compressed buffer. * * (*) checked once in the beginning of lz77_compress() */ static __always_inline u32 lz77_compressed_alloc_size(const u32 size) { return size + (size >> 3) + 8; } int lz77_compress(const void *src, const u32 slen, void *dst, u32 *dlen); #endif /* _SMB_COMPRESS_LZ77_H */