shithub: cstory

Info  •  Files  •  Log  •  Branches

Fix an occational invalid memory read

Stupid floating-point rounding errors. Had to undo a fancy
optimisation to avoid it.

--- a/src/Backends/Audio/SDL2.cpp

+++ b/src/Backends/Audio/SDL2.cpp

@@ -75,28 +75,21 @@

 		{

 			float *steam_pointer = stream;

-			unsigned int frames_done = 0;

-

-			while (frames_done != frames_total)

+			for (unsigned int frames_done = 0; frames_done < frames_total; ++frames_done)

 			{

-				const unsigned int frames_to_do = MIN((unsigned int)ceil((sound->frames - sound->position) / sound->advance_delta), frames_total - frames_done);

+				// Get two samples, and normalise them to 0-1

+				const float sample1 = (sound->samples[(size_t)sound->position] - 128.0f) / 128.0f;

+				const float sample2 = (sound->samples[(size_t)sound->position + 1] - 128.0f) / 128.0f;

-				for (unsigned int i = 0; i < frames_to_do; ++i)

-				{

-					// Get two samples, and normalise them to 0-1

-					const float sample1 = (sound->samples[(size_t)sound->position] - 128.0f) / 128.0f;

-					const float sample2 = (sound->samples[(size_t)sound->position + 1] - 128.0f) / 128.0f;

+				// Perform linear interpolation

+				const float interpolated_sample = sample1 + ((sample2 - sample1) * (float)fmod(sound->position, 1.0));

-					// Perform linear interpolation

-					const float interpolated_sample = sample1 + ((sample2 - sample1) * (float)fmod(sound->position, 1.0));

+				*steam_pointer++ += interpolated_sample * sound->volume_l;

+				*steam_pointer++ += interpolated_sample * sound->volume_r;

-					*steam_pointer++ += interpolated_sample * sound->volume_l;

-					*steam_pointer++ += interpolated_sample * sound->volume_r;

+				sound->position += sound->advance_delta;

-					sound->position += sound->advance_delta;

-				}

-

-				if ((size_t)sound->position >= sound->frames)

+				if (sound->position >= sound->frames)

 				{

 					if (sound->looping)

 					{

@@ -109,8 +102,6 @@

 						break;

 					}

 				}

-

-				frames_done += frames_to_do;

 			}

 		}

 	}