Re: [PATCH 1/1] LZ4: Port LZ4 1.9.x FAST_DEC_LOOP and enable it on x86 and ARM64

From: Gao Xiang
Date: Wed May 15 2019 - 21:49:18 EST

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On 2019/5/16 7:48, Mao, Chenxi wrote:
> Hi Yann and Xiang:
> For this FAST_DEC_LOOP change, I only pick up decompress related patches to current kernel LZ4 implementation(based on 1.8.3).
> Here is my cherry-pick list:
> 2589c44 created LZ4_FAST_DEC_LOOP build macro
> 605d811 enable LZ4_FAST_DEC_LOOP build macro on aarch64/GCC by default
> 5d7d116 decompress_generic: Limit fastpath to x86
> 75fb878 decompress_generic: Add fastpath for small offsets
> faac110 decompress_generic: Unroll loops a bit more
> 1fbaf84 decompress_generic: remove msan write
> 28b8249 decompress_generic: re-add fastpath
> 232f1e2 decompress_generic: drop partial copy check in fast loop
> 59332a3 decompress_generic: Optimize literal copies
> 5dfa7d4 decompress_generic: optimize match copy
> 28356e0 decompress_generic: Add a loop fastpath
> 4da3360 decompress_generic: Refactor variable length fields
>
> Only cherry-pick these changes to LZ4 1.8.3 would not be introduce risks.

The fact is that ... LZ4_FAST_DEC_LOOP almost influences all decompression apis.
You should keep LZ4_decompress_generic from all known issues.

>
> @Xiang:
> Do you prefer to upgrade kernel lz4 to 1.9.1 directly or only pick some optimization patches?

I think you should pick all patches which are related to LZ4_decompress_generic()
and LZ4_FAST_DEC_LOOP since known issues of LZ4_FAST_DEC_LOOP should be fixed of course.

Thanks,
Gao Xiang

>
> Chenxi
>
>
> On 5/16/19 1:47 AM, Gao Xiang wrote:
>> Hi Yann,
>>
>> On 2019/5/16 1:03, Cyan wrote:
>>> Re-posted,
>>> it seems the previous message was rejected by the linux-kernel server
>>> due to some kind of format limitation (no html).
>>>
>>>
>>> Le mer. 15 mai 2019 Ã 09:56, Cyan <yann.collet.73@xxxxxxxxx> a Ãcrit :
>>>>
>>>> The v1.9.0 version has a bug which makes it read a few bytes out of bound in certain cases.
>>>> This was fixed in v1.9.1.
>>>> Therefore, if you plan upgrading version, skip directly to v1.9.1.
>>>>
>>>> Note that, in v1.9.1, LZ4_decompress_fast() is now deprecated.
>>>> LZ4_decompress_fast() is a security liability, since it's unable to cope with malicious inputs.
>>>> While this is not a problem when the producer is under direct control (local production and consumption, no intermediate storage),
>>>> this entry point seems misused in multiple scenarios where input cannot be decently trusted.
>>>> The deprecation warning is meant to "scare away" such usages.
>>>> It's still possible to intentionally remove the warning, for users who know what they are doing.
>>>>
>>>> Note that, on top of that, the _fast() variant is now slower that LZ4_decompress_safe(), removing its most important positive differentiator.
>>>> That's because LZ4_decompress_fast() is "blind", it doesn't know the input size.
>>>> It just guesses it, from the requested output size, and by relying on end-of-block conditions.
>>>> This effectively limits its capability to copy up to 8 bytes at a time,
>>>> which proves slower than the 32-bytes at a time used in LZ4_decompress_safe().
>>>>
>>>> LZ4_decompress_fast() still has some possible usage :
>>>> it doesn't need the compressed size.
>>>> Therefore, in a scenario where decompressed size is known, but compressed size isn't,
>>>> it cannot be replaced by `LZ4_decompress_safe()`.
>>>> This is pretty rare, but can happen in some cases, erofs for example.
>>>> `LZ4_decompress_safe_partial()` *might* be able to replace it for such scenario,
>>>> but I haven't thoroughly tested it, so can't yet vouch for it.
>>
>> Yes, that is my real concern...
>>
>> In fact, we have shipped erofs with LZ4_decompress_safe_partial() of lz4-1.8.3
>> for our HUAWEI P30/P30 Pro and other HUAWEI EMUI 9.1 phones on the market...
>>
>> It seemd lz4-1.8.3 is rather stable since no stability report from our internal
>> beta test and real consumers...
>>
>> I haven't tested lz4-1.9.0 yet since I am working on the erofs paper [1]...
>>
>> But anyway, the patch looks good to me since it has obvious performance gain...
>>
>>>>
>>>> If it doesn't, then it will be necessary to create a new entry point.
>>>> The main difference is that this new entry point will need a bound for the input size, in order to guarantee it never reads beyond input buffer.
>>>> But as said, for the time being, such dedicated entry point doesn't exist.
>>
>> I agree, but current erofs still have to choose LZ4_decompress_fast...
>> I will test these 2 apis later and will report if something is wrong as well.
>>
>> [1] https://www.usenix.org/conference/atc19/presentation/gao
>> https://www.usenix.org/conference/atc19/technical-sessions
>>
>> Thanks,
>> Gao Xiang
>>
>>
>>>>
>>>> The new FAST_DEC_LOOP setting works well on x86 and x64.
>>>> Recently, it has been extended to gcc+arm64 (`dev` branch).
>>>> The combination of clang+arm64 is less successful though (impacts vary, depending on version and exact hardware), so it's still disabled by default.
>>>> But anyone can test it by setting FAST_DEC_LOOP definition to 1, thus enabling the new decoder loop.
>>>>
>>>>
>>>> Y.
>>>>
>>>> Le mar. 14 mai 2019 Ã 20:28, Mao, Chenxi <Chenxi.Mao@xxxxxxxx> a Ãcrit :
>>>>>
>>>>> Hi Xiang:
>>>>>
>>>>> Thanks for your reply, I will have a stress test on my device later.
>>>>> I didn't have chance to test LZ4 with clang build because of device limitation. I think I could do it later.
>>>>> I guess the clang performance downgrade is caused by some compiler optimization options.
>>>>> I will double check it later if I got the device which can build kernel with clang.
>>>>>
>>>>> BTW, the FAST_DEC_LOOP leverage LZ4_wildCopy8 instead of LZ4_wildCopy,
>>>>> however based on my test, original LZ4_wildCopy has the better performance.
>>>>> Original LZ4_wildCopy API still invoked by FAST_DEC_LOOP apis.
>>>>> That might be a problem for X86 devices for current patch.
>>>>>
>>>>> Chenxi
>>>>>
>>>>> -----Original Message-----
>>>>> From: Gao Xiang [mailto:gaoxiang25@xxxxxxxxxx]
>>>>> Sent: Wednesday, May 15, 2019 10:21 AM
>>>>> To: Mao, Chenxi <Chenxi.Mao@xxxxxxxx>
>>>>> Cc: akpm@xxxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; Feng, Roy <Roy.Feng@xxxxxxxx>; Xu, Yuanli 2 <Yuanli.Xu@xxxxxxxx>; Alm, Robert 2 <Robert.Alm@xxxxxxxx>; Takahashi, Masaya A (Sony Mobile) <Masaya.A.Takahashi@xxxxxxxx>; Miao Xie <miaoxie@xxxxxxxxxx>
>>>>> Subject: Re: [PATCH 1/1] LZ4: Port LZ4 1.9.x FAST_DEC_LOOP and enable it on x86 and ARM64
>>>>>
>>>>> Hi Chenxi,
>>>>>
>>>>> On 2019/5/15 8:43, Chenxi Mao wrote:
>>>>>> FAST_DEC_LOOP was introduced from LZ4 1.9.
>>>>>> This change would be introduce 10% on decompress operation according
>>>>>> to LZ4 benchmark result on X86 devices.
>>>>>> Meanwhile, LZ4 with FAST_DEC_LOOP could get improvements, however
>>>>>> clang compiler has downgrade if FAST_DEC_LOOP enabled.
>>>>>
>>>>> I noticed this optimization and lz4-1.9.0 [1] was just released month ago with this big change therefore I'm a little afraid of its current stability (especially some rare used decompression apis...)
>>>>>
>>>>> Could you Cc more people (e.g. lz4 original author Yann Collet) in order to get some more ideas about this if possible?
>>>>>
>>>>> Anyway, I like this optimization as well since FAST_DEC_LOOP improves decompression speed a lot :)
>>>>>
>>>>> [1] https://github.com/lz4/lz4/releases/tag/v1.9.0
>>>>>
>>>>> Thanks,
>>>>> Gao Xiang
>>>>>
>>>>>>
>>>>>> So FAST_DEC_LOOP only enabled on X86/X86-64 or ARM64 with GCC build.
>>>>>>
>>>>>> Here is the test result on ARM64(cortex-A53)
>>>>>>
>>>>>> Benchmark via ZRAM:
>>>>>>
>>>>>> Test case:
>>>>>> fio --bs=32k --randrepeat=1 --randseed=100 --refill_buffers \
>>>>>> --buffer_compress_percentage=75 \
>>>>>> --scramble_buffers=1 --direct=1 --loops=100 --numjobs=8 \
>>>>>> --filename=/dev/block/zram0 --name=seq-write --rw=write --stonewall \
>>>>>> --name=seq-read --rw=read --stonewall --name=seq-readwrite \ --rw=rw
>>>>>> --stonewall --name=rand-readwrite --rw=randrw --stonewall
>>>>>>
>>>>>> Patched:
>>>>>> READ: bw=7077MiB/s (7421MB/s)
>>>>>> Vanilla:
>>>>>> READ: bw=5134MiB/s (5384MB/s)
>>>>>>
>>>>>> Reference:
>>>>>> 1. https://github.com/lz4/lz4/pull/645
>>>>>> 2. https://github.com/lz4/lz4/pull/707
>>>>>>
>>>>>> Signed-off-by: chenxi.mao <chenxi.mao@xxxxxxxx>
>>>>>> ---
>>>>>> lib/lz4/lz4_decompress.c | 425
>>>>>> +++++++++++++++++++++++++++++++++------
>>>>>> 1 file changed, 361 insertions(+), 64 deletions(-)
>>>>>>
>>>>>> diff --git a/lib/lz4/lz4_decompress.c b/lib/lz4/lz4_decompress.c index
>>>>>> 0c9d3ad17e0f..a4c87e32b3c0 100644
>>>>>> --- a/lib/lz4/lz4_decompress.c
>>>>>> +++ b/lib/lz4/lz4_decompress.c
>>>>>> @@ -50,6 +50,131 @@
>>>>>> #define assert(condition) ((void)0)
>>>>>> #endif
>>>>>>
>>>>>> +#ifndef LZ4_FAST_DEC_LOOP
>>>>>> +#if defined(__i386__) || defined(__x86_64__) #define
>>>>>> +LZ4_FAST_DEC_LOOP 1 #elif defined(__aarch64__) && !defined(__clang__)
>>>>>> + /* On aarch64, we disable this optimization for clang because on certain
>>>>>> + * mobile chipsets and clang, it reduces performance. For more information
>>>>>> + * refer to https://github.com/lz4/lz4/pull/707. */ #define
>>>>>> +LZ4_FAST_DEC_LOOP 1 #else #define LZ4_FAST_DEC_LOOP 0 #endif #endif
>>>>>> +
>>>>>> +static const unsigned inc32table[8] = { 0, 1, 2, 1, 0, 4, 4, 4 };
>>>>>> +static const int dec64table[8] = { 0, 0, 0, -1, -4, 1, 2, 3 };
>>>>>> +
>>>>>> +#if LZ4_FAST_DEC_LOOP
>>>>>> +#define FASTLOOP_SAFE_DISTANCE 64
>>>>>> +FORCE_INLINE void
>>>>>> +LZ4_memcpy_using_offset_base(BYTE * dstPtr, const BYTE * srcPtr, BYTE * dstEnd,
>>>>>> + const size_t offset)
>>>>>> +{
>>>>>> + if (offset < 8) {
>>>>>> + dstPtr[0] = srcPtr[0];
>>>>>> +
>>>>>> + dstPtr[1] = srcPtr[1];
>>>>>> + dstPtr[2] = srcPtr[2];
>>>>>> + dstPtr[3] = srcPtr[3];
>>>>>> + srcPtr += inc32table[offset];
>>>>>> + memcpy(dstPtr + 4, srcPtr, 4);
>>>>>> + srcPtr -= dec64table[offset];
>>>>>> + dstPtr += 8;
>>>>>> + } else {
>>>>>> + memcpy(dstPtr, srcPtr, 8);
>>>>>> + dstPtr += 8;
>>>>>> + srcPtr += 8;
>>>>>> + }
>>>>>> +
>>>>>> + LZ4_wildCopy(dstPtr, srcPtr, dstEnd); }
>>>>>> +
>>>>>> +/* customized variant of memcpy, which can overwrite up to 32 bytes
>>>>>> +beyond dstEnd
>>>>>> + * this version copies two times 16 bytes (instead of one time 32
>>>>>> +bytes)
>>>>>> + * because it must be compatible with offsets >= 16. */ FORCE_INLINE
>>>>>> +void LZ4_wildCopy32(void *dstPtr, const void *srcPtr, void *dstEnd) {
>>>>>> + BYTE *d = (BYTE *) dstPtr;
>>>>>> + const BYTE *s = (const BYTE *)srcPtr;
>>>>>> + BYTE *const e = (BYTE *) dstEnd;
>>>>>> +
>>>>>> + do {
>>>>>> + memcpy(d, s, 16);
>>>>>> + memcpy(d + 16, s + 16, 16);
>>>>>> + d += 32;
>>>>>> + s += 32;
>>>>>> + } while (d < e);
>>>>>> +}
>>>>>> +
>>>>>> +FORCE_INLINE void
>>>>>> +LZ4_memcpy_using_offset(BYTE *dstPtr, const BYTE *srcPtr, BYTE *dstEnd,
>>>>>> + const size_t offset)
>>>>>> +{
>>>>>> + BYTE v[8];
>>>>>> + switch (offset) {
>>>>>> +
>>>>>> + case 1:
>>>>>> + memset(v, *srcPtr, 8);
>>>>>> + goto copy_loop;
>>>>>> + case 2:
>>>>>> + memcpy(v, srcPtr, 2);
>>>>>> + memcpy(&v[2], srcPtr, 2);
>>>>>> + memcpy(&v[4], &v[0], 4);
>>>>>> + goto copy_loop;
>>>>>> + case 4:
>>>>>> + memcpy(v, srcPtr, 4);
>>>>>> + memcpy(&v[4], srcPtr, 4);
>>>>>> + goto copy_loop;
>>>>>> + default:
>>>>>> + LZ4_memcpy_using_offset_base(dstPtr, srcPtr, dstEnd, offset);
>>>>>> + return;
>>>>>> + }
>>>>>> +
>>>>>> + copy_loop:
>>>>>> + memcpy(dstPtr, v, 8);
>>>>>> + dstPtr += 8;
>>>>>> + while (dstPtr < dstEnd) {
>>>>>> + memcpy(dstPtr, v, 8);
>>>>>> + dstPtr += 8;
>>>>>> + }
>>>>>> +}
>>>>>> +
>>>>>> +/* Read the variable-length literal or match length.
>>>>>> + *
>>>>>> + * ip - pointer to use as input.
>>>>>> + * lencheck - end ip. Return an error if ip advances >= lencheck.
>>>>>> + * loop_check - check ip >= lencheck in body of loop. Returns loop_error if so.
>>>>>> + * initial_check - check ip >= lencheck before start of loop. Returns initial_error if so.
>>>>>> + * error (output) - error code. Should be set to 0 before call.
>>>>>> + */
>>>>>> +typedef enum { loop_error = -2, initial_error = -1, ok = 0}
>>>>>> +variable_length_error; FORCE_INLINE unsigned read_variable_length(const BYTE **ip,
>>>>>> + const BYTE *lencheck,
>>>>>> + int loop_check, int initial_check,
>>>>>> + variable_length_error *error) {
>>>>>> + unsigned length = 0;
>>>>>> + unsigned s;
>>>>>> + if (initial_check && unlikely((*ip) >= lencheck)) { /* overflow detection */
>>>>>> + *error = initial_error;
>>>>>> + return length;
>>>>>> + }
>>>>>> + do {
>>>>>> + s = **ip;
>>>>>> + (*ip)++;
>>>>>> + length += s;
>>>>>> + if (loop_check && unlikely((*ip) >= lencheck)) { /* overflow detection */
>>>>>> + *error = loop_error;
>>>>>> + return length;
>>>>>> + }
>>>>>> + } while (s == 255);
>>>>>> +
>>>>>> + return length;
>>>>>> +}
>>>>>> +#endif
>>>>>> +
>>>>>> /*
>>>>>> * LZ4_decompress_generic() :
>>>>>> * This generic decompression function covers all use cases.
>>>>>> @@ -80,25 +205,28 @@ static FORCE_INLINE int LZ4_decompress_generic(
>>>>>> const size_t dictSize
>>>>>> )
>>>>>> {
>>>>>> - const BYTE *ip = (const BYTE *) src;
>>>>>> - const BYTE * const iend = ip + srcSize;
>>>>>> + const BYTE *ip = (const BYTE *)src;
>>>>>> + const BYTE *const iend = ip + srcSize;
>>>>>>
>>>>>> BYTE *op = (BYTE *) dst;
>>>>>> - BYTE * const oend = op + outputSize;
>>>>>> + BYTE *const oend = op + outputSize;
>>>>>> BYTE *cpy;
>>>>>>
>>>>>> - const BYTE * const dictEnd = (const BYTE *)dictStart + dictSize;
>>>>>> - static const unsigned int inc32table[8] = {0, 1, 2, 1, 0, 4, 4, 4};
>>>>>> - static const int dec64table[8] = {0, 0, 0, -1, -4, 1, 2, 3};
>>>>>> + const BYTE *const dictEnd = (const BYTE *)dictStart + dictSize;
>>>>>>
>>>>>> const int safeDecode = (endOnInput == endOnInputSize);
>>>>>> const int checkOffset = ((safeDecode) && (dictSize < (int)(64 *
>>>>>> KB)));
>>>>>>
>>>>>> /* Set up the "end" pointers for the shortcut. */
>>>>>> const BYTE *const shortiend = iend -
>>>>>> - (endOnInput ? 14 : 8) /*maxLL*/ - 2 /*offset*/;
>>>>>> + (endOnInput ? 14 : 8) /*maxLL*/ - 2 /*offset*/;
>>>>>> const BYTE *const shortoend = oend -
>>>>>> - (endOnInput ? 14 : 8) /*maxLL*/ - 18 /*maxML*/;
>>>>>> + (endOnInput ? 14 : 8) /*maxLL*/ - 18 /*maxML*/;
>>>>>> +
>>>>>> + const BYTE *match;
>>>>>> + size_t offset;
>>>>>> + unsigned int token;
>>>>>> + size_t length;
>>>>>>
>>>>>> DEBUGLOG(5, "%s (srcSize:%i, dstSize:%i)", __func__,
>>>>>> srcSize, outputSize);
>>>>>> @@ -117,15 +245,194 @@ static FORCE_INLINE int LZ4_decompress_generic(
>>>>>> if ((endOnInput) && unlikely(srcSize == 0))
>>>>>> return -1;
>>>>>>
>>>>>> - /* Main Loop : decode sequences */
>>>>>> +#if LZ4_FAST_DEC_LOOP
>>>>>> + if ((oend - op) < FASTLOOP_SAFE_DISTANCE) {
>>>>>> + DEBUGLOG(6, "skip fast decode loop");
>>>>>> + goto safe_decode;
>>>>>> + }
>>>>>> +
>>>>>> + /* Fast loop : decode sequences as long as output <
>>>>>> +iend-FASTLOOP_SAFE_DISTANCE */
>>>>>> while (1) {
>>>>>> - size_t length;
>>>>>> - const BYTE *match;
>>>>>> - size_t offset;
>>>>>> + /* Main fastloop assertion: We can always wildcopy FASTLOOP_SAFE_DISTANCE */
>>>>>> + assert(oend - op >= FASTLOOP_SAFE_DISTANCE);
>>>>>> + if (endOnInput) {
>>>>>> + assert(ip < iend);
>>>>>> + }
>>>>>> + token = *ip++;
>>>>>> + length = token >> ML_BITS; /* literal length */
>>>>>> +
>>>>>> + assert(!endOnInput || ip <= iend); /* ip < iend before the increment */
>>>>>> +
>>>>>> + /* decode literal length */
>>>>>> + if (length == RUN_MASK) {
>>>>>> + variable_length_error error = ok;
>>>>>> + length +=
>>>>>> + read_variable_length(&ip, iend - RUN_MASK,
>>>>>> + endOnInput, endOnInput,
>>>>>> + &error);
>>>>>> + if (error == initial_error) {
>>>>>> + goto _output_error;
>>>>>> + }
>>>>>> + if ((safeDecode)
>>>>>> + && unlikely((uptrval) (op) + length <
>>>>>> + (uptrval) (op))) {
>>>>>> + goto _output_error;
>>>>>> + } /* overflow detection */
>>>>>> + if ((safeDecode)
>>>>>> + && unlikely((uptrval) (ip) + length <
>>>>>> + (uptrval) (ip))) {
>>>>>> + goto _output_error;
>>>>>> + }
>>>>>> +
>>>>>> + /* overflow detection */
>>>>>> + /* copy literals */
>>>>>> + cpy = op + length;
>>>>>> + LZ4_STATIC_ASSERT(MFLIMIT >= WILDCOPYLENGTH);
>>>>>> + if (endOnInput) { /* LZ4_decompress_safe() */
>>>>>> + if ((cpy > oend - 32)
>>>>>> + || (ip + length > iend - 32)) {
>>>>>> + goto safe_literal_copy;
>>>>>> + }
>>>>>> + LZ4_wildCopy32(op, ip, cpy);
>>>>>> + } else { /* LZ4_decompress_fast() */
>>>>>> + if (cpy > oend - 8) {
>>>>>> + goto safe_literal_copy;
>>>>>> + }
>>>>>> + LZ4_wildCopy(op, ip, cpy);
>>>>>> + /* LZ4_decompress_fast() cannot copy more than 8 bytes at a time */
>>>>>> + /* it doesn't know input length, and only relies on end-of-block */
>>>>>> + /* properties */
>>>>>> + }
>>>>>> + ip += length;
>>>>>> + op = cpy;
>>>>>> + } else {
>>>>>> + cpy = op + length;
>>>>>> + if (endOnInput) { /* LZ4_decompress_safe() */
>>>>>> + DEBUGLOG(7,
>>>>>> + "copy %u bytes in a 16-bytes stripe",
>>>>>> + (unsigned)length);
>>>>>> + /* We don't need to check oend */
>>>>>> + /* since we check it once for each loop below */
>>>>>> + if (ip > iend - (16 + 1)) { /*max lit + offset + nextToken */
>>>>>> + goto safe_literal_copy;
>>>>>> + }
>>>>>> + /* Literals can only be 14, but hope compilers optimize */
>>>>>> + /*if we copy by a register size */
>>>>>> + memcpy(op, ip, 16);
>>>>>> + } else {
>>>>>> + /* LZ4_decompress_fast() cannot copy more than 8 bytes at a time */
>>>>>> + /* it doesn't know input length, and relies on end-of-block */
>>>>>> + /* properties */
>>>>>> + memcpy(op, ip, 8);
>>>>>> + if (length > 8) {
>>>>>> + memcpy(op + 8, ip + 8, 8);
>>>>>> + }
>>>>>> + }
>>>>>> + ip += length;
>>>>>> + op = cpy;
>>>>>> + }
>>>>>> +
>>>>>> + /* get offset */
>>>>>> + offset = LZ4_readLE16(ip);
>>>>>> + ip += 2; /* end-of-block condition violated */
>>>>>> + match = op - offset;
>>>>>> +
>>>>>> + /* get matchlength */
>>>>>> + length = token & ML_MASK;
>>>>>>
>>>>>> - /* get literal length */
>>>>>> - unsigned int const token = *ip++;
>>>>>> - length = token>>ML_BITS;
>>>>>> + if ((checkOffset) && (unlikely(match + dictSize < lowPrefix))) {
>>>>>> + goto _output_error;
>>>>>> + }
>>>>>> + /* Error : offset outside buffers */
>>>>>> + if (length == ML_MASK) {
>>>>>> + variable_length_error error = ok;
>>>>>> + length +=
>>>>>> + read_variable_length(&ip, iend - LASTLITERALS + 1,
>>>>>> + endOnInput, 0, &error);
>>>>>> + if (error != ok) {
>>>>>> + goto _output_error;
>>>>>> + }
>>>>>> + if ((safeDecode)
>>>>>> + && unlikely((uptrval) (op) + length < (uptrval) op)) {
>>>>>> + goto _output_error;
>>>>>> + } /* overflow detection */
>>>>>> + length += MINMATCH;
>>>>>> + if (op + length >= oend - FASTLOOP_SAFE_DISTANCE) {
>>>>>> + goto safe_match_copy;
>>>>>> + }
>>>>>> + } else {
>>>>>> + length += MINMATCH;
>>>>>> + if (op + length >= oend - FASTLOOP_SAFE_DISTANCE) {
>>>>>> + goto safe_match_copy;
>>>>>> + }
>>>>>> +
>>>>>> + /* Fastpath check: Avoids a branch in LZ4_wildCopy32 if true */
>>>>>> + if (!(dict == usingExtDict) || (match >= lowPrefix)) {
>>>>>> + if (offset >= 8) {
>>>>>> + memcpy(op, match, 8);
>>>>>> + memcpy(op + 8, match + 8, 8);
>>>>>> + memcpy(op + 16, match + 16, 2);
>>>>>> + op += length;
>>>>>> + continue;
>>>>>> + }
>>>>>> + }
>>>>>> + }
>>>>>> +
>>>>>> + /* match starting within external dictionary */
>>>>>> + if ((dict == usingExtDict) && (match < lowPrefix)) {
>>>>>> + if (unlikely(op + length > oend - LASTLITERALS)) {
>>>>>> + if (partialDecoding) {
>>>>>> + /* reach end of buffer */
>>>>>> + length =
>>>>>> + min(length, (size_t) (oend - op));
>>>>>> + } else {
>>>>>> + /* end-of-block condition violated */
>>>>>> + goto _output_error;
>>>>>> + }
>>>>>> + }
>>>>>> +
>>>>>> + if (length <= (size_t) (lowPrefix - match)) {
>>>>>> + /* match fits entirely within external dictionary : just copy */
>>>>>> + memmove(op, dictEnd - (lowPrefix - match), length);
>>>>>> + op += length;
>>>>>> + } else {
>>>>>> + /* match stretches into both external dict and current block */
>>>>>> + size_t const copySize =
>>>>>> + (size_t) (lowPrefix - match);
>>>>>> + size_t const restSize = length - copySize;
>>>>>> + memcpy(op, dictEnd - copySize, copySize);
>>>>>> + op += copySize;
>>>>>> + if (restSize > (size_t) (op - lowPrefix)) { /* overlap copy */
>>>>>> + BYTE *const endOfMatch = op + restSize;
>>>>>> + const BYTE *copyFrom = lowPrefix;
>>>>>> + while (op < endOfMatch) {
>>>>>> + *op++ = *copyFrom++;
>>>>>> + }
>>>>>> + } else {
>>>>>> + memcpy(op, lowPrefix, restSize);
>>>>>> + op += restSize;
>>>>>> + }
>>>>>> + }
>>>>>> + continue;
>>>>>> + }
>>>>>> +
>>>>>> + /* copy match within block */
>>>>>> + cpy = op + length;
>>>>>> +
>>>>>> + assert((op <= oend) && (oend - op >= 32));
>>>>>> + if (unlikely(offset < 16)) {
>>>>>> + LZ4_memcpy_using_offset(op, match, cpy, offset);
>>>>>> + } else {
>>>>>> + LZ4_wildCopy32(op, match, cpy);
>>>>>> + }
>>>>>> +
>>>>>> + op = cpy; /* wildcopy correction */
>>>>>> + }
>>>>>> + safe_decode:
>>>>>> +#endif
>>>>>> + /* Main Loop : decode sequences */
>>>>>> + while (1) {
>>>>>> + length = token >> ML_BITS;
>>>>>>
>>>>>> /* ip < iend before the increment */
>>>>>> assert(!endOnInput || ip <= iend);
>>>>>> @@ -143,26 +450,27 @@ static FORCE_INLINE int LZ4_decompress_generic(
>>>>>> * combined check for both stages).
>>>>>> */
>>>>>> if ((endOnInput ? length != RUN_MASK : length <= 8)
>>>>>> - /*
>>>>>> - * strictly "less than" on input, to re-enter
>>>>>> - * the loop with at least one byte
>>>>>> - */
>>>>>> - && likely((endOnInput ? ip < shortiend : 1) &
>>>>>> - (op <= shortoend))) {
>>>>>> + /*
>>>>>> + * strictly "less than" on input, to re-enter
>>>>>> + * the loop with at least one byte
>>>>>> + */
>>>>>> + && likely((endOnInput ? ip < shortiend : 1) &
>>>>>> + (op <= shortoend))) {
>>>>>> /* Copy the literals */
>>>>>> memcpy(op, ip, endOnInput ? 16 : 8);
>>>>>> - op += length; ip += length;
>>>>>> + op += length;
>>>>>> + ip += length;
>>>>>>
>>>>>> /*
>>>>>> * The second stage:
>>>>>> * prepare for match copying, decode full info.
>>>>>> * If it doesn't work out, the info won't be wasted.
>>>>>> */
>>>>>> - length = token & ML_MASK; /* match length */
>>>>>> + length = token & ML_MASK; /* match length */
>>>>>> offset = LZ4_readLE16(ip);
>>>>>> ip += 2;
>>>>>> match = op - offset;
>>>>>> - assert(match <= op); /* check overflow */
>>>>>> + assert(match <= op); /* check overflow */
>>>>>>
>>>>>> /* Do not deal with overlapping matches. */
>>>>>> if ((length != ML_MASK) &&
>>>>>> @@ -187,28 +495,24 @@ static FORCE_INLINE int LZ4_decompress_generic(
>>>>>>
>>>>>> /* decode literal length */
>>>>>> if (length == RUN_MASK) {
>>>>>> - unsigned int s;
>>>>>>
>>>>>> - if (unlikely(endOnInput ? ip >= iend - RUN_MASK : 0)) {
>>>>>> - /* overflow detection */
>>>>>> + variable_length_error error = ok;
>>>>>> + length +=
>>>>>> + read_variable_length(&ip, iend - RUN_MASK,
>>>>>> + endOnInput, endOnInput,
>>>>>> + &error);
>>>>>> + if (error == initial_error)
>>>>>> goto _output_error;
>>>>>> - }
>>>>>> - do {
>>>>>> - s = *ip++;
>>>>>> - length += s;
>>>>>> - } while (likely(endOnInput
>>>>>> - ? ip < iend - RUN_MASK
>>>>>> - : 1) & (s == 255));
>>>>>>
>>>>>> if ((safeDecode)
>>>>>> - && unlikely((uptrval)(op) +
>>>>>> - length < (uptrval)(op))) {
>>>>>> + && unlikely((uptrval) (op) +
>>>>>> + length < (uptrval) (op))) {
>>>>>> /* overflow detection */
>>>>>> goto _output_error;
>>>>>> }
>>>>>> if ((safeDecode)
>>>>>> - && unlikely((uptrval)(ip) +
>>>>>> - length < (uptrval)(ip))) {
>>>>>> + && unlikely((uptrval) (ip) +
>>>>>> + length < (uptrval) (ip))) {
>>>>>> /* overflow detection */
>>>>>> goto _output_error;
>>>>>> }
>>>>>> @@ -216,11 +520,15 @@ static FORCE_INLINE int LZ4_decompress_generic(
>>>>>>
>>>>>> /* copy literals */
>>>>>> cpy = op + length;
>>>>>> +#if LZ4_FAST_DEC_LOOP
>>>>>> + safe_literal_copy:
>>>>>> +#endif
>>>>>> LZ4_STATIC_ASSERT(MFLIMIT >= WILDCOPYLENGTH);
>>>>>>
>>>>>> if (((endOnInput) && ((cpy > oend - MFLIMIT)
>>>>>> - || (ip + length > iend - (2 + 1 + LASTLITERALS))))
>>>>>> - || ((!endOnInput) && (cpy > oend - WILDCOPYLENGTH))) {
>>>>>> + || (ip + length >
>>>>>> + iend - (2 + 1 + LASTLITERALS))))
>>>>>> + || ((!endOnInput) && (cpy > oend - WILDCOPYLENGTH))) {
>>>>>> if (partialDecoding) {
>>>>>> if (cpy > oend) {
>>>>>> /*
>>>>>> @@ -231,7 +539,7 @@ static FORCE_INLINE int LZ4_decompress_generic(
>>>>>> length = oend - op;
>>>>>> }
>>>>>> if ((endOnInput)
>>>>>> - && (ip + length > iend)) {
>>>>>> + && (ip + length > iend)) {
>>>>>> /*
>>>>>> * Error :
>>>>>> * read attempt beyond
>>>>>> @@ -241,7 +549,7 @@ static FORCE_INLINE int LZ4_decompress_generic(
>>>>>> }
>>>>>> } else {
>>>>>> if ((!endOnInput)
>>>>>> - && (cpy != oend)) {
>>>>>> + && (cpy != oend)) {
>>>>>> /*
>>>>>> * Error :
>>>>>> * block decoding must
>>>>>> @@ -250,7 +558,7 @@ static FORCE_INLINE int LZ4_decompress_generic(
>>>>>> goto _output_error;
>>>>>> }
>>>>>> if ((endOnInput)
>>>>>> - && ((ip + length != iend)
>>>>>> + && ((ip + length != iend)
>>>>>> || (cpy > oend))) {
>>>>>> /*
>>>>>> * Error :
>>>>>> @@ -288,29 +596,14 @@ static FORCE_INLINE int LZ4_decompress_generic(
>>>>>> goto _output_error;
>>>>>> }
>>>>>>
>>>>>> - /* costs ~1%; silence an msan warning when offset == 0 */
>>>>>> - /*
>>>>>> - * note : when partialDecoding, there is no guarantee that
>>>>>> - * at least 4 bytes remain available in output buffer
>>>>>> - */
>>>>>> - if (!partialDecoding) {
>>>>>> - assert(oend > op);
>>>>>> - assert(oend - op >= 4);
>>>>>> -
>>>>>> - LZ4_write32(op, (U32)offset);
>>>>>> - }
>>>>>> -
>>>>>> if (length == ML_MASK) {
>>>>>> - unsigned int s;
>>>>>> -
>>>>>> - do {
>>>>>> - s = *ip++;
>>>>>> -
>>>>>> - if ((endOnInput) && (ip > iend - LASTLITERALS))
>>>>>> - goto _output_error;
>>>>>>
>>>>>> - length += s;
>>>>>> - } while (s == 255);
>>>>>> + variable_length_error error = ok;
>>>>>> + length +=
>>>>>> + read_variable_length(&ip, iend - LASTLITERALS + 1,
>>>>>> + endOnInput, 0, &error);
>>>>>> + if (error != ok)
>>>>>> + goto _output_error;
>>>>>>
>>>>>> if ((safeDecode)
>>>>>> && unlikely(
>>>>>> @@ -322,6 +615,10 @@ static FORCE_INLINE int LZ4_decompress_generic(
>>>>>>
>>>>>> length += MINMATCH;
>>>>>>
>>>>>> +#if LZ4_FAST_DEC_LOOP
>>>>>> +safe_match_copy:
>>>>>> +#endif
>>>>>> +
>>>>>> /* match starting within external dictionary */
>>>>>> if ((dict == usingExtDict) && (match < lowPrefix)) {
>>>>>> if (unlikely(op + length > oend - LASTLITERALS)) {
>>>>>>

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