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SubjectRe: [PATCH 1/1] LZ4: Port LZ4 1.9.x FAST_DEC_LOOP and enable it on x86 and ARM64
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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@gmail.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@sony.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@huawei.com]
>>> Sent: Wednesday, May 15, 2019 10:21 AM
>>> To: Mao, Chenxi <Chenxi.Mao@sony.com>
>>> Cc: akpm@linux-foundation.org; linux-kernel@vger.kernel.org; Feng, Roy <Roy.Feng@sony.com>; Xu, Yuanli 2 <Yuanli.Xu@sony.com>; Alm, Robert 2 <Robert.Alm@sony.com>; Takahashi, Masaya A (Sony Mobile) <Masaya.A.Takahashi@sony.com>; Miao Xie <miaoxie@huawei.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@sony.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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