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Date:   Thu, 16 May 2019 10:07:39 +0800
From:   "Mao, Chenxi" <Chenxi.Mao@...y.com>
To:     Gao Xiang <gaoxiang25@...wei.com>
CC:     Cyan <yann.collet.73@...il.com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Feng, Roy" <Roy.Feng@...y.com>,
        "Xu, Yuanli 2" <Yuanli.Xu@...y.com>,
        "Alm, Robert 2" <Robert.Alm@...y.com>,
        "Takahashi, Masaya A (Sony Mobile)" <Masaya.A.Takahashi@...y.com>,
        Miao Xie <miaoxie@...wei.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH 1/1] LZ4: Port LZ4 1.9.x FAST_DEC_LOOP and enable it on
 x86 and ARM64

Hi Xiang:

I checked the deliver history.
There is only below delivery related with lz4.c
Pull request:616
4e3accc Fix Dict Size Test in `LZ4_compress_fast_continue()`
535636f Don't Attach Very Small Dictionaries
This 2 changes seems like ONLY bug fixes for dictionary fix baesd on 1.8.3

Based on current investigation result, I think pick decompress patches is safe for v1.8.3

If there is any misunderstanding or faults, please feel free to let me know.

Chenxi

On 5/16/19 9:35 AM, Gao Xiang wrote:
> 
> 
> 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 à 09:56, Cyan <yann.collet.73@...il.com> a écrit :
>>>>>
>>>>> 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 à 20:28, Mao, Chenxi <Chenxi.Mao@...y.com> a écrit :
>>>>>>
>>>>>> 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@...wei.com]
>>>>>> Sent: Wednesday, May 15, 2019 10:21 AM
>>>>>> To: Mao, Chenxi <Chenxi.Mao@...y.com>
>>>>>> Cc: akpm@...ux-foundation.org; linux-kernel@...r.kernel.org; Feng, Roy <Roy.Feng@...y.com>; Xu, Yuanli 2 <Yuanli.Xu@...y.com>; Alm, Robert 2 <Robert.Alm@...y.com>; Takahashi, Masaya A (Sony Mobile) <Masaya.A.Takahashi@...y.com>; Miao Xie <miaoxie@...wei.com>
>>>>>> 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@...y.com>
>>>>>>> ---
>>>>>>>  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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