I'm working on a comparison of WebAssembly performance for error propagation dithering using D, C++ and Zig. So far C++ and Zig work as expected, but for D, despite using the same algorithm and similar code the output is different.

You can see the differences here https://wasm-error-propagation-dither-comparison.netlify.app/ by opening an image.

Code

• D https://github.com/allen-garvey/wasm-error-propagation-dither-comparison/blob/master/wasm/d/main.d
• C++ https://github.com/allen-garvey/wasm-error-propagation-dither-comparison/blob/master/wasm/cpp/main.cpp
• Zig https://github.com/allen-garvey/wasm-error-propagation-dither-comparison/blob/master/wasm/zig/main.zig

Any help would be appreciated. From my extensive debugging it seems that calculating the pixel lightness is working correctly, it has something to do with either saving or retrieving the stored error in the float arrays.

The problem is the memset signature. You assume the length is the number of floats, while it's the number of bytes to be set to the specified value. https://en.cppreference.com/w/c/string/byte/memset

On Monday, 16 May 2022 at 18:14:13 UTC, kinke wrote:

Thanks so much, that fixed the problem! You have no idea have long I have spent trying to debug this!

On Monday, 16 May 2022 at 17:32:20 UTC, Allen Garvey wrote:

Hm D version is the slowest one?!

On Tuesday, 17 May 2022 at 09:38:31 UTC, Sergey wrote:

It's faster than the JS version atleast. But yeah, C++ and Zig being 30+% faster than the D solution doesn't look good on us :(

On Tuesday, 17 May 2022 at 11:36:21 UTC, Adam D Ruppe wrote:

Looks like you forgot to increment the pointer and need "*d++ = cast(ubyte) c;" there. And filling the buffer one byte at a time is likely slow.