After updating to version 1.5.1 of the library I noticed that compression speeds were much worse compared to version 1.4.9 at the same compression level. In my benchmarks for my use case, which is compressing streaming network data, zlib now beats zstd with regard to speed and output size.

To reproduce, build the attached source file first with version 1.4.9 used as a DLL, check the output, and then do the same with version 1.5.1 and check the output after running the program.

On my PC running Windows 10 and using Visual Studio 2022 to build, I get the following results with compressionlevel 10:

with zstd 1.4.9: duration: 512 ms, output size: 422 bytes
with zstd 1.5.1: duration: 71266 ms, output size: 422 bytes

Even with compression level 1 there is a difference; 1.5.1 is slower than 1.4.9 albeit not by much compared to compression level 10.

Where does this huge difference in duration come from?

Source.zip