Add comments, and avoid throw-away calculations in crossfade buffer process
git-svn-id: svn://svn.rockbox.org/rockbox/trunk@9352 a1c6a512-1295-4272-9138-f99709370657
diff --git a/apps/pcmbuf.c b/apps/pcmbuf.c
index 41719d8..79a412c 100644
--- a/apps/pcmbuf.c
+++ b/apps/pcmbuf.c
@@ -451,35 +451,43 @@
/**
* Completely process the crossfade fade out effect with current pcm buffer.
*/
-static void crossfade_process_buffer(unsigned int fade_in_delay,
- unsigned int fade_out_delay, size_t fade_out_rem)
+static void crossfade_process_buffer(size_t fade_in_delay,
+ size_t fade_out_delay, size_t fade_out_rem)
{
- size_t amount;
- size_t pos;
- short *buf;
-
- /* Fade out the entire current buffer according to settings. */
- amount = fade_out_rem;
- pos = crossfade_pos + fade_out_delay*2;
-
- while (fade_out_rem > 0 && crossfade_mode == CFM_CROSSFADE)
+ if (crossfade_mode == CFM_CROSSFADE)
{
- size_t blocksize = MIN(8192, fade_out_rem);
- int factor = (fade_out_rem<<8)/amount;
+ /* Fade out the specified amount of the already processed audio */
+ size_t total_fade_out = fade_out_rem;
+ short *buf = (short *)&audiobuffer[crossfade_pos + fade_out_delay * 2];
+ short *buf_end = (short *)guardbuf;
- /* Prevent pcmbuffer from wrapping. */
- if (pos >= pcmbuf_size) pos -= pcmbuf_size;
+ /* Wrap the starting position if needed */
+ if (buf >= buf_end) buf -= pcmbuf_size / 2;
- blocksize = MIN((pcmbuf_size - pos)/2, blocksize);
- buf = (short *)&audiobuffer[pos];
-
- fade_out_rem -= blocksize;
- pos += blocksize * 2;
- while (blocksize > 0)
+ while (fade_out_rem > 0)
{
- *buf = (*buf * factor) >> 8;
- *buf++;
- blocksize--;
+ /* Each 1/10 second of audio will have the same fade applied */
+ size_t block_rem = MIN(NATIVE_FREQUENCY * 2 / 10, fade_out_rem);
+ unsigned int factor = (fade_out_rem << 8) / total_fade_out;
+ short *block_end = buf + block_rem;
+
+ fade_out_rem -= block_rem;
+
+ /* Fade this block */
+ while (buf < block_end)
+ {
+ /* Fade one sample */
+ *buf = (*buf * factor) >> 8;
+ buf++;
+
+ if (buf >= buf_end)
+ {
+ /* Wrap the pcmbuffer */
+ buf -= pcmbuf_size / 2;
+ /* Wrap the end pointer to ensure proper termination */
+ block_end -= pcmbuf_size / 2;
+ }
+ }
}
}