From 29694869b1ba37fee71b407f61ccaee0c03a8d63 Mon Sep 17 00:00:00 2001
From: "Ryan C. Gordon" <[EMAIL REDACTED]>
Date: Thu, 28 Apr 2022 15:56:52 -0400
Subject: [PATCH] audio: Revert one of the resampler optimizations.
This is the one that splits the "left wing" into two for loops to
bubble out the conditional that decides if it should read from the
left padding or the input buffer.
I still believe the optimization is good, but the basic logic of it
was incorrect, and needs to be reexamined and fixed before going
back into revision control.
---
src/audio/SDL_audiocvt.c | 18 ++++--------------
1 file changed, 4 insertions(+), 14 deletions(-)
diff --git a/src/audio/SDL_audiocvt.c b/src/audio/SDL_audiocvt.c
index 6ecc2c9ff4b..0b95b417c75 100644
--- a/src/audio/SDL_audiocvt.c
+++ b/src/audio/SDL_audiocvt.c
@@ -757,21 +757,11 @@ SDL_ResampleAudio(const int chans, const int inrate, const int outrate,
float outsample = 0.0f;
/* do this twice to calculate the sample, once for the "left wing" and then same for the right. */
-
- /* Left wing! split the "srcframe < 0" condition out into a preloop. */
- for (j = 0; srcindex < j; j++) {
- const int jsamples = j * RESAMPLER_SAMPLES_PER_ZERO_CROSSING;
- const int srcframe = srcindex - j;
- const float insample = lpadding[((paddinglen + srcframe) * chans) + chan];
- outsample += (float)(insample * (ResamplerFilter[filterindex1 + jsamples] + (interpolation1 * ResamplerFilterDifference[filterindex1 + jsamples])));
- }
-
- /* Finish the left wing now that srcframe >= 0 */
- for (; (filterindex1 + (j * RESAMPLER_SAMPLES_PER_ZERO_CROSSING)) < RESAMPLER_FILTER_SIZE; j++) {
- const int jsamples = j * RESAMPLER_SAMPLES_PER_ZERO_CROSSING;
+ for (j = 0; (filterindex1 + (j * RESAMPLER_SAMPLES_PER_ZERO_CROSSING)) < RESAMPLER_FILTER_SIZE; j++) {
const int srcframe = srcindex - j;
- const float insample = inbuf[(srcframe * chans) + chan];
- outsample += (float)(insample * (ResamplerFilter[filterindex1 + jsamples] + (interpolation1 * ResamplerFilterDifference[filterindex1 + jsamples])));
+ /* !!! FIXME: we can bubble this conditional out of here by doing a pre loop. */
+ const float insample = (srcframe < 0) ? lpadding[((paddinglen + srcframe) * chans) + chan] : inbuf[(srcframe * chans) + chan];
+ outsample += (float)(insample * (ResamplerFilter[filterindex1 + (j * RESAMPLER_SAMPLES_PER_ZERO_CROSSING)] + (interpolation1 * ResamplerFilterDifference[filterindex1 + (j * RESAMPLER_SAMPLES_PER_ZERO_CROSSING)])));
}
/* Do the right wing! */