Minor LodePNG optimizations #173
Open
Conversation
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Also correct typo and update build command to link SDL2 and not SDL
zvezdochiot
reviewed
Sep 18, 2022
| @@ -3256,33 +3256,28 @@ static void getPixelColorRGBA8(unsigned char* r, unsigned char* g, | |||
| if(mode->colortype == LCT_GREY) { | |||
| if(mode->bitdepth == 8) { | |||
| *r = *g = *b = in[i]; | |||
| if(mode->key_defined && *r == mode->key_r) *a = 0; | |||
| else *a = 255; | |||
| *a = 255 * !(mode->key_defined && *r == mode->key_r); | |||
There was a problem hiding this comment.
❓ Why use multiplication where it is unnecessary?:
*a = ((mode->key_defined) && (*r == mode->key_r)) ? 0u : 255u;Or use array?:
unsigned char wb[2] = {255, 0);
...
*a = wb[(int)((mode->key_defined) && (*r == mode->key_r))];(for const time).
There was a problem hiding this comment.
Each conversion from if-else statement to multiplication in this case removes one jump instruction, creating code that has a few less branches and is also slightly smaller
There was a problem hiding this comment.
I tested this out with godbolt.org, and it looks like the way you write it doesn't matter, the effect is equivalent and it gets compiled to the same thing:
So the original with if/else looks more readable I'd say
Encoding speeds up by ~1% when compiled with -O3 on Clang 15.0.0
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
LodePNG code size is decreased by about 1.5kB when compiled with MSYS2 CLANG64 Clang 15.0.0
Decoding (RGB and non-alpha grey colortypes) and encoding (any colortype) should be about 1-2% faster
A warning is fixed in lodepng_benchmark.cpp so it can successfully be compiled with the recommended build command