Add generic C versions of the fast decoding loops to serve architectures
that don't have an assembly implementation. Also allow selecting the C
decoding loop over the assembly decoding loop through a zstd
decompression parameter `ZSTD_d_disableHuffmanAssembly`.
I benchmarked on my Intel i9-9900K and my Macbook Air with an M1 processor.
The benchmark command forces zstd to compress without any matches, using
only literals compression, and measures only Huffman decompression speed:
```
zstd -b1e1 --compress-literals --zstd=tlen=131072 silesia.tar
```
The new fast decoding loops outperform the previous implementation uniformly,
but don't beat the x86-64 assembly. Additionally, the fast C decoding loops suffer
from the same stability problems that we've seen in the past, where the assembly
version doesn't. So even though clang gets close to assembly on x86-64, it still
has stability issues.
| Arch | Function | Compiler | Default (MB/s) | Assembly (MB/s) | Fast (MB/s) |
|---------|----------------|--------------|----------------|-----------------|-------------|
| x86-64 | decompress 4X1 | gcc-12.2.0 | 1029.6 | 1308.1 | 1208.1 |
| x86-64 | decompress 4X1 | clang-14.0.6 | 1019.3 | 1305.6 | 1276.3 |
| x86-64 | decompress 4X2 | gcc-12.2.0 | 1348.5 | 1657.0 | 1374.1 |
| x86-64 | decompress 4X2 | clang-14.0.6 | 1027.6 | 1659.9 | 1468.1 |
| aarch64 | decompress 4X1 | clang-12.0.5 | 1081.0 | N/A | 1234.9 |
| aarch64 | decompress 4X2 | clang-12.0.5 | 1270.0 | N/A | 1516.6 |
```
for f in $(find . \( -path ./.git -o -path ./tests/fuzz/corpora \) -prune -o -type f);
do
sed -i 's/Facebook, Inc\./Meta Platforms, Inc. and affiliates./' $f;
done
```
Intel Control-flow Enforcement Technology (CET):
https://en.wikipedia.org/wiki/Control-flow_integrity#Intel_Control-flow_Enforcement_Technology
requires that on Linux, all linker input files are marked as CET enabled
in .note.gnu.property section. For high-level language source codes,
.note.gnu.property section is added by compiler with the -fcf-protection
option. For assembly sources, include <cet.h> to add .note.gnu.property
section.
Move portability macros to `lib/common/portability_macros.h`. This file
only contains platform/feature detection (e.g. 0/1 macros). This file is
shared between C and ASM code, so it cannot include any C code.
Rename `HUF_` ASM macros to be `ZSTD_` prefixed, and move to the new
header.
Restrict `ZSTD_ASM_SUPPORTED` to `__GNUC__`, because we need the GAS
assembler.
Finally, only include the ASM code if we are actually going to use it.
This disables it on all Windows platforms, which should resolve the
problem brought up in Issue #2789.
