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min_max_sse: design failsafe for lenghts not mod.4

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Moreno Razzoli
2021-10-13 22:58:04 +02:00
parent 7beb9f0595
commit 3656ed480e
1 changed files with 35 additions and 22 deletions
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app/audio/audiovisualwaveform.cpp
+35 -22
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@@ -17,11 +17,9 @@
along with this program. If not, see <http://www.gnu.org/licenses/>.
***/
#if defined(__x86_64__) || defined(_M_X64)
#define x86_64
#endif
#include <QtGlobal>
#ifdef x86_64
#ifdef Q_PROCESSOR_X86_64
#include <xmmintrin.h>
#endif
@@ -293,23 +291,38 @@ AudioVisualWaveform::Sample AudioVisualWaveform::SumSamples(const float *samples
return summed_samples;
}
#ifdef x86_64
void min_max_sse(float *a, int start, int end, float &min_val, float &max_val) {
// for time being just assume that length is always mod 4
__m128 max = _mm_loadu_ps(a + start); // load the first 4
__m128 min = _mm_loadu_ps(a + start); // load the first 4
for(int i = 4; i < end; i+=4)
{
__m128 cur = _mm_loadu_ps(a + start + i);
max = _mm_max_ps(max, cur);
min = _mm_min_ps(min, cur);
}
for (int i = 0; i < 3; i++) {
max = _mm_max_ps(max, _mm_shuffle_ps(max, max, 0x93));
min = _mm_min_ps(min, _mm_shuffle_ps(min, min, 0x93));
}
_mm_store_ss(&max_val, max);
_mm_store_ss(&min_val, min);
#ifdef Q_PROCESSOR_X86_64
void min_max_sse(float *a, int start, int end, float &min_val, float &max_val)
{
// load the first 4 elements of 'a' into min and max (they are 4 * 32 = 128 bits)
__m128 max = _mm_loadu_ps(a + start);
__m128 min = _mm_loadu_ps(a + start);
// loop over 'a' and compare current elements with min and max 4 by 4.
// we need to make sure we don't read out of boundaries should 'a' lenght be not mod. 4
for(int i = 4; i < end-4; i+=4) {
__m128 cur = _mm_loadu_ps(a + start + i);
max = _mm_max_ps(max, cur);
min = _mm_min_ps(min, cur);
}
// so we read the last 4 (or less) elements in a safe manner.
__m128 cur = _mm_loadu_ps(a + end - 4);
max = _mm_max_ps(max, cur);
min = _mm_min_ps(min, cur);
// this potentially overlaps up to the last 3 elements but it's not an issue.
// min and max will contain 4 min and max. To get the absolute min and max
// we need to compare the 4 values over themselves by shuffling each time.
for (int i = 0; i < 3; i++) {
max = _mm_max_ps(max, _mm_shuffle_ps(max, max, 0x93));
min = _mm_min_ps(min, _mm_shuffle_ps(min, min, 0x93));
}
// now min and max contain 4 identical items each representing min and max value respectively.
// and we store the first one into a float variable.
_mm_store_ss(&max_val, max);
_mm_store_ss(&min_val, min);
// I bet you don't find annotated low level code very often.
}
#endif
@@ -318,7 +331,7 @@ AudioVisualWaveform::Sample AudioVisualWaveform::SumSamples(SampleBufferPtr samp
int channels = samples->audio_params().channel_count();
AudioVisualWaveform::Sample summed_samples(channels);
#ifdef x86_64
#ifdef Q_PROCESSOR_X86_64
for (int channel=0; channel<samples->audio_params().channel_count(); channel++) {
min_max_sse(samples->data(channel), start_index, length, summed_samples[channel].min, summed_samples[channel].max);
}