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Add comments, and avoid throw-away calculations in crossfade buffer process

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git-svn-id: svn://svn.rockbox.org/rockbox/trunk@9352 a1c6a512-1295-4272-9138-f99709370657
This commit is contained in:
Brandon Low 2006-03-30 00:47:05 +00:00
parent 4ed232df5e
commit dbcc9c25d5
1 changed files with 32 additions and 24 deletions
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56
apps/pcmbuf.c
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@ -451,35 +451,43 @@ static void pcmbuf_flush_fillpos(void)
/**
* 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;
}
}
}
}