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Fix compilation warning #11

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@kxepal kxepal commented Oct 26, 2015

snappy.cc: In member function ‘void snappy::SnappySinkAllocator::Flush(size_t)’:
snappy.cc:1336:38: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (int i = 0; i < blocks_.size(); ++i) {

This warning doesn't shows with current compilation options, but it does when you compile snappy with -Wall flag.

snappy.cc: In member function ‘void snappy::SnappySinkAllocator::Flush(size_t)’:
snappy.cc:1336:38: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (int i = 0; i < blocks_.size(); ++i) {
kxepal added a commit to kxepal/couchdb-snappy that referenced this pull request Oct 26, 2015
kxepal added a commit to kxepal/couchdb-snappy that referenced this pull request Nov 10, 2015
ncopa pushed a commit to ncopa/snappy that referenced this pull request Feb 22, 2017
The commit 8bfb028 (Improve zippy decompression speed) introduce a crash
when snappy is compiled with _FORTIFY_SOURCE with musl libc. Backtrace
reveals that it it comes from using memcpy with overlap, which is
undefined behavior.

We avoid the undefined behavior due to memcpy with overlap by using a
temporary uint64_t.

Bactrace from core dump created with `make check`:
````
(gdb) bt
 #0  memcpy (__n=8, __os=0xb38c8367eea, __od=0xb38c8367eeb)
     at /usr/include/fortify/string.h:48
 google#1  snappy::(anonymous namespace)::UnalignedCopy64 (src=0xb38c8367eea,
     dst=0xb38c8367eeb) at snappy.cc:92
 google#2  0x00006fb4c7c31717 in snappy::(anonymous namespace)::IncrementalCopy
 (
     buf_limit=0xb38c8380ee0 "", op_limit=<optimized out>, op=<optimized
 out>,
     src=0xb38c8367eea " .\001") at snappy.cc:178
 google#3  snappy::SnappyArrayWriter::AppendFromSelf (len=<optimized out>,
     offset=<optimized out>, this=<synthetic pointer>) at snappy.cc:1131
 google#4
 snappy::SnappyDecompressor::DecompressAllTags<snappy::SnappyArrayWriter>
 (
     writer=<synthetic pointer>, this=0x7f1d26737050) at snappy.cc:715
 google#5  snappy::InternalUncompressAllTags<snappy::SnappyArrayWriter> (
     uncompressed_len=<optimized out>, writer=<synthetic pointer>,
     decompressor=0x7f1d26737050) at snappy.cc:799
 google#6  snappy::InternalUncompress<snappy::SnappyArrayWriter> (
     writer=<synthetic pointer>, r=0x7f1d26737000) at snappy.cc:789
 google#7  snappy::RawUncompress (compressed=compressed@entry=0x7f1d267370c0,
     uncompressed=0xb38c8367ee0 "  content: .\001") at snappy.cc:1149
 google#8  0x00006fb4c7c3194d in snappy::RawUncompress (compressed=<optimized
 out>,
     n=<optimized out>, uncompressed=<optimized out>) at snappy.cc:1144
 google#9  0x00000b38c5c6261a in snappy::BM_UFlat (iters=99, arg=<optimized
 out>)
     at snappy_unittest.cc:1371
 google#10 0x00000b38c5c69846 in snappy::Benchmark::Run (this=0xb38c8323c40)
     at snappy-test.cc:192
 google#11 0x00000b38c5c5f3fd in RunSpecifiedBenchmarks () at snappy-test.h:485
 google#12 main (argc=1, argv=0x7f1d267374b8) at snappy_unittest.cc:1515
````

Signed-off-by: Natanael Copa <[email protected]>
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@kxepal kxepal closed this May 14, 2019
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kxepal commented May 14, 2019

Thanks for ping, but this PR is no longer actual. And nowday there are far more warnings on master than it was in 2015 year, so there should be another solution.

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