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// SPDX-License-Identifier: GPL-2.0-only
/*
* Copyright (C) 2024, SUSE LLC
*
* Authors: Enzo Matsumiya <ematsumiya@suse.de>
*
* Implementation of the LZ77 "plain" compression algorithm, as per MS-XCA spec.
*/
#include <linux/slab.h>
#include <linux/sizes.h>
#include <linux/count_zeros.h>
#include <linux/unaligned.h>
#include "lz77.h"
/*
* Compression parameters.
*/
#define LZ77_MATCH_MIN_LEN 4
#define LZ77_MATCH_MIN_DIST 1
#define LZ77_MATCH_MAX_DIST SZ_1K
#define LZ77_HASH_LOG 15
#define LZ77_HASH_SIZE (1 << LZ77_HASH_LOG)
#define LZ77_STEP_SIZE sizeof(u64)
static __always_inline u8 lz77_read8(const u8 *ptr)
{
return get_unaligned(ptr);
}
static __always_inline u64 lz77_read64(const u64 *ptr)
{
return get_unaligned(ptr);
}
static __always_inline void lz77_write8(u8 *ptr, u8 v)
{
put_unaligned(v, ptr);
}
static __always_inline void lz77_write16(u16 *ptr, u16 v)
{
put_unaligned_le16(v, ptr);
}
static __always_inline void lz77_write32(u32 *ptr, u32 v)
{
put_unaligned_le32(v, ptr);
}
static __always_inline u32 lz77_match_len(const void *wnd, const void *cur, const void *end)
{
const void *start = cur;
u64 diff;
/* Safe for a do/while because otherwise we wouldn't reach here from the main loop. */
do {
diff = lz77_read64(cur) ^ lz77_read64(wnd);
if (!diff) {
cur += LZ77_STEP_SIZE;
wnd += LZ77_STEP_SIZE;
continue;
}
/* This computes the number of common bytes in @diff. */
cur += count_trailing_zeros(diff) >> 3;
return (cur - start);
} while (likely(cur + LZ77_STEP_SIZE < end));
while (cur < end && lz77_read8(cur++) == lz77_read8(wnd++))
;
return (cur - start);
}
static __always_inline void *lz77_write_match(void *dst, void **nib, u32 dist, u32 len)
{
len -= 3;
dist--;
dist <<= 3;
if (len < 7) {
lz77_write16(dst, dist + len);
return dst + 2;
}
dist |= 7;
lz77_write16(dst, dist);
dst += 2;
len -= 7;
if (!*nib) {
lz77_write8(dst, umin(len, 15));
*nib = dst;
dst++;
} else {
u8 *b = *nib;
lz77_write8(b, *b | umin(len, 15) << 4);
*nib = NULL;
}
if (len < 15)
return dst;
len -= 15;
if (len < 255) {
lz77_write8(dst, len);
return dst + 1;
}
lz77_write8(dst, 0xff);
dst++;
len += 7 + 15;
if (len <= 0xffff) {
lz77_write16(dst, len);
return dst + 2;
}
lz77_write16(dst, 0);
dst += 2;
lz77_write32(dst, len);
return dst + 4;
}
noinline int lz77_compress(const void *src, u32 slen, void *dst, u32 *dlen)
{
const void *srcp, *end;
void *dstp, *nib, *flag_pos;
u32 flag_count = 0;
long flag = 0;
u64 *htable;
srcp = src;
end = src + slen;
dstp = dst;
nib = NULL;
flag_pos = dstp;
dstp += 4;
htable = kvcalloc(LZ77_HASH_SIZE, sizeof(*htable), GFP_KERNEL);
if (!htable)
return -ENOMEM;
/* Main loop. */
do {
u32 dist, len = 0;
const void *wnd;
u64 hash;
hash = ((lz77_read64(srcp) << 24) * 889523592379ULL) >> (64 - LZ77_HASH_LOG);
wnd = src + htable[hash];
htable[hash] = srcp - src;
dist = srcp - wnd;
if (dist && dist < LZ77_MATCH_MAX_DIST)
len = lz77_match_len(wnd, srcp, end);
if (len < LZ77_MATCH_MIN_LEN) {
lz77_write8(dstp, lz77_read8(srcp));
dstp++;
srcp++;
flag <<= 1;
flag_count++;
if (flag_count == 32) {
lz77_write32(flag_pos, flag);
flag_count = 0;
flag_pos = dstp;
dstp += 4;
}
continue;
}
/*
* Bail out if @dstp reached >= 7/8 of @slen -- already compressed badly, not worth
* going further.
*/
if (unlikely(dstp - dst >= slen - (slen >> 3))) {
*dlen = slen;
goto out;
}
dstp = lz77_write_match(dstp, &nib, dist, len);
srcp += len;
flag = (flag << 1) | 1;
flag_count++;
if (flag_count == 32) {
lz77_write32(flag_pos, flag);
flag_count = 0;
flag_pos = dstp;
dstp += 4;
}
} while (likely(srcp + LZ77_STEP_SIZE < end));
while (srcp < end) {
u32 c = umin(end - srcp, 32 - flag_count);
memcpy(dstp, srcp, c);
dstp += c;
srcp += c;
flag <<= c;
flag_count += c;
if (flag_count == 32) {
lz77_write32(flag_pos, flag);
flag_count = 0;
flag_pos = dstp;
dstp += 4;
}
}
flag <<= (32 - flag_count);
flag |= (1 << (32 - flag_count)) - 1;
lz77_write32(flag_pos, flag);
*dlen = dstp - dst;
out:
kvfree(htable);
if (*dlen < slen)
return 0;
return -EMSGSIZE;
}
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