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Spectrum analyser: optimise the x:16:2 case

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nncmpp CPU usage went from 2 to 1.7 percent, a 15% improvement.

Sort of worth it, given that it's a constant load.

The assembly certainly looks nicer.
This commit is contained in:
Přemysl Eric Janouch 2021-07-08 19:07:42 +02:00
parent fa4443a3ce
commit 20c8385f2e
Signed by: p
GPG Key ID: A0420B94F92B9493
1 changed files with 21 additions and 8 deletions
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nncmpp.c
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@ -638,13 +638,13 @@ spectrum_decode_8 (struct spectrum *s, int sample)
{
size_t n = s->useful_bins;
float *data = s->data + n;
int8_t *p = (int8_t *) s->buffer + sample * n * s->channels;
while (n--)
for (int8_t *p = (int8_t *) s->buffer + sample * n * s->channels;
n--; p += s->channels)
{
int32_t acc = 0;
for (int ch = 0; ch < s->channels; ch++)
acc += *p++;
*data++ = (float) acc / -INT8_MIN / s->channels;
acc += p[ch];
*data++ = (float) acc / s->channels / -INT8_MIN;
}
}
@ -653,16 +653,25 @@ spectrum_decode_16 (struct spectrum *s, int sample)
{
size_t n = s->useful_bins;
float *data = s->data + n;
int16_t *p = (int16_t *) s->buffer + sample * n * s->channels;
while (n--)
for (int16_t *p = (int16_t *) s->buffer + sample * n * s->channels;
n--; p += s->channels)
{
int32_t acc = 0;
for (int ch = 0; ch < s->channels; ch++)
acc += *p++;
*data++ = (float) acc / -INT16_MIN / s->channels;
acc += p[ch];
*data++ = (float) acc / s->channels / -INT16_MIN;
}
}
static void
spectrum_decode_16_2 (struct spectrum *s, int sample)
{
size_t n = s->useful_bins;
float *data = s->data + n;
for (int16_t *p = (int16_t *) s->buffer + sample * n * 2; n--; p += 2)
*data++ = ((int32_t) p[0] + p[1]) / 2. / -INT16_MIN;
}
// - - Spectrum analysis - - - - - - - - - - - - - - - - - - - - - - - - - - - -
static const char *spectrum_bars[] =
@ -803,6 +812,10 @@ spectrum_init (struct spectrum *s, char *format, int bars, struct error **e)
if (s->bits == 8) s->decode = spectrum_decode_8;
if (s->bits == 16) s->decode = spectrum_decode_16;
// Micro-optimize to achieve some piece of mind; it's weak but measurable
if (s->bits == 16 && s->channels == 2)
s->decode = spectrum_decode_16_2;
s->buffer_size = s->samples * s->useful_bins * s->bits / 8 * s->channels;
s->buffer = xcalloc (1, s->buffer_size);