Simplifying loops for performance: why check dropSamplesAtEnd in every
iteration, when we could modify the loop boundary? The (writable)
variable samplesLeft can be eliminated; add a write-once variable
pcm_length instead, which is used for the loop condition.
---
src/inputPlugins/mp3_plugin.c | 39 ++++++++++++++++++---------------------
1 files changed, 18 insertions(+), 21 deletions(-)
diff --git a/src/inputPlugins/mp3_plugin.c b/src/inputPlugins/mp3_plugin.c
index 7eb527e..2a6346b 100644
--- a/src/inputPlugins/mp3_plugin.c
+++ b/src/inputPlugins/mp3_plugin.c
@@ -839,7 +839,7 @@ static int openMp3FromInputStream(InputStream * inStream,
mp3DecodeData * data,
static int mp3Read(mp3DecodeData * data, struct decoder *decoder,
ReplayGainInfo ** replayGainInfo)
{
- unsigned int samplesLeft;
+ unsigned int pcm_length;
unsigned int i;
int ret;
int skip;
@@ -917,32 +917,23 @@ static int mp3Read(mp3DecodeData * data, struct decoder
*decoder,
freeMpdTag(tag);
}
- samplesLeft = (data->synth).pcm.length;
-
if (!data->decodedFirstFrame) {
- if (data->dropSamplesAtStart >= samplesLeft) {
- i = samplesLeft;
- samplesLeft = 0;
- } else {
- i = data->dropSamplesAtStart;
- samplesLeft -= data->dropSamplesAtStart;
- }
+ i = data->dropSamplesAtStart;
data->decodedFirstFrame = 1;
} else
i = 0;
- for (; i < (data->synth).pcm.length; i++) {
- unsigned int num_samples;
-
- samplesLeft--;
+ pcm_length = data->synth.pcm.length;
+ if (data->dropSamplesAtEnd &&
+ (data->currentFrame == data->maxFrames -
data->dropFramesAtEnd)) {
+ if (data->dropSamplesAtEnd >= pcm_length)
+ pcm_length = 0;
+ else
+ pcm_length -= data->dropSamplesAtEnd;
+ }
- if (data->dropSamplesAtEnd &&
- (data->currentFrame == (data->maxFrames -
data->dropFramesAtEnd)) &&
- (samplesLeft < data->dropSamplesAtEnd)) {
- /* stop decoding, effectively dropping
- * all remaining samples */
- return DECODE_BREAK;
- }
+ for (; i < pcm_length; i++) {
+ unsigned int num_samples;
num_samples = dither_buffer((mpd_sint16 *)
data->outputPtr,
&data->synth, &data->dither,
@@ -968,6 +959,12 @@ static int mp3Read(mp3DecodeData * data, struct decoder
*decoder,
}
}
+ if (data->dropSamplesAtEnd &&
+ (data->currentFrame == data->maxFrames -
data->dropFramesAtEnd))
+ /* stop decoding, effectively dropping
+ * all remaining samples */
+ return DECODE_BREAK;
+
if (decoder_get_command(decoder) == DECODE_COMMAND_SEEK &&
data->inStream->seekable) {
unsigned long j = 0;
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