From 072e3fdfc437a87832d4ff569e8e1393abe251ae Mon Sep 17 00:00:00 2001
From: Sylvain <[EMAIL REDACTED]>
Date: Thu, 14 Oct 2021 23:17:08 +0200
Subject: [PATCH] Fixed bug #4534: NEON implementation of Convert51ToStereo
(Thanks Ryan!)
---
src/audio/SDL_audiocvt.c | 74 ++++++++++++++++++++++++++++++++++++++--
1 file changed, 72 insertions(+), 2 deletions(-)
diff --git a/src/audio/SDL_audiocvt.c b/src/audio/SDL_audiocvt.c
index 225ced6661..f0cb7e6e40 100644
--- a/src/audio/SDL_audiocvt.c
+++ b/src/audio/SDL_audiocvt.c
@@ -35,6 +35,10 @@
#define DEBUG_AUDIOSTREAM 0
+#ifdef __ARM_NEON
+#define HAVE_NEON_INTRINSICS 1
+#endif
+
#ifdef __SSE__
#define HAVE_SSE_INTRINSICS 1
#endif
@@ -240,6 +244,66 @@ SDL_Convert51ToStereo_SSE(SDL_AudioCVT * cvt, SDL_AudioFormat format)
}
#endif
+#if HAVE_NEON_INTRINSICS
+/* Convert from 5.1 to stereo. Average left and right, distribute center, discard LFE. */
+static void SDLCALL
+SDL_Convert51ToStereo_NEON(SDL_AudioCVT * cvt, SDL_AudioFormat format)
+{
+ float *dst = (float *) cvt->buf;
+ const float *src = dst;
+ int i = cvt->len_cvt / (sizeof (float) * 6);
+ const float two_fifths_f = 1.0f / 2.5f;
+ const float32x4_t two_fifths_v = vdupq_n_f32(two_fifths_f);
+ const float32x4_t half = vdupq_n_f32(0.5f);
+
+ LOG_DEBUG_CONVERT("5.1", "stereo (using NEON)");
+ SDL_assert(format == AUDIO_F32SYS);
+
+ /* SDL's 5.1 layout: FL+FR+FC+LFE+BL+BR */
+
+ /* Just use unaligned load/stores, it's the same NEON instructions and
+ hopefully even unaligned NEON is faster than the scalar fallback. */
+ while (i >= 2) {
+ /* Two 5.1 samples (12 floats) fit nicely in three 128bit */
+ /* registers. Using shuffles they can be rearranged so that */
+ /* the conversion math can be vectorized. */
+ const float32x4_t in0 = vld1q_f32(src); /* 0FL 0FR 0FC 0LF */
+ const float32x4_t in1 = vld1q_f32(src + 4); /* 0BL 0BR 1FL 1FR */
+ const float32x4_t in2 = vld1q_f32(src + 8); /* 1FC 1LF 1BL 1BR */
+
+ /* 0FC 0FC 1FC 1FC */
+ const float32x4_t fc_distributed = vmulq_f32(half, vcombine_f32(vdup_lane_f32(vget_high_f32(in0), 0), vdup_lane_f32(vget_low_f32(in2), 0)));
+
+ /* 0FL 0FR 1BL 1BR */
+ const float32x4_t blended = vcombine_f32(vget_low_f32(in0), vget_high_f32(in2));
+
+ /* 0FL 0FR 1BL 1BR */
+ /* + 0BL 0BR 1FL 1FR */
+ /* = 0L 0R 1L 1R */
+ float32x4_t out = vaddq_f32(blended, in1);
+ out = vaddq_f32(out, fc_distributed);
+ out = vmulq_f32(out, two_fifths_v);
+
+ vst1q_f32(dst, out);
+
+ i -= 2; src += 12; dst += 4;
+ }
+
+ /* Finish off any leftovers with scalar operations. */
+ while (i) {
+ const float front_center_distributed = src[2] * 0.5f;
+ dst[0] = (src[0] + front_center_distributed + src[4]) * two_fifths_f; /* left */
+ dst[1] = (src[1] + front_center_distributed + src[5]) * two_fifths_f; /* right */
+ i--; src += 6; dst+=2;
+ }
+
+ cvt->len_cvt /= 3;
+ if (cvt->filters[++cvt->filter_index]) {
+ cvt->filters[cvt->filter_index] (cvt, format);
+ }
+}
+#endif
+
/* Convert from 5.1 to stereo. Average left and right, distribute center, discard LFE. */
static void SDLCALL
SDL_Convert51ToStereo(SDL_AudioCVT * cvt, SDL_AudioFormat format)
@@ -1177,6 +1241,12 @@ SDL_BuildAudioCVT(SDL_AudioCVT * cvt,
}
#endif
+ #if HAVE_NEON_INTRINSICS
+ if (!filter && SDL_HasNEON()) {
+ filter = SDL_Convert51ToStereo_NEON;
+ }
+ #endif
+
if (!filter) {
filter = SDL_Convert51ToStereo;
}
@@ -1231,7 +1301,7 @@ SDL_BuildAudioCVT(SDL_AudioCVT * cvt,
handled by now, but let's be defensive */
return SDL_SetError("Invalid channel combination");
}
-
+
/* Do rate conversion, if necessary. Updates (cvt). */
if (SDL_BuildAudioResampleCVT(cvt, dst_channels, src_rate, dst_rate) < 0) {
return -1; /* shouldn't happen, but just in case... */
@@ -1713,7 +1783,7 @@ SDL_AudioStreamPut(SDL_AudioStream *stream, const void *buf, int len)
stream->staging_buffer_filled += len;
return 0;
}
-
+
/* Fill the staging buffer, process it, and continue */
amount = (stream->staging_buffer_size - stream->staging_buffer_filled);
SDL_assert(amount > 0);