[pulseaudio-discuss] [PATCH 5/6] core: add stereo to mono special case remapping

[Peter Meerwald]

From: Peter Meerwald <p.meerwald at bct-electronic.com>

add special-case C code for stereo-to-mone remapping

compiled with Ubuntu/Linaro gcc 4.6.1:
arm-linux-gnueabi-gcc-O2 -mcpu=cortex-a8 -mfloat-abi=softfp -mfpu=neon

runtime on beagle-xm, 800 MHz (ref is the special-case C impl, generic
is the catch-all matrix implementation):

checking NEON remap_mono_to_stereo(float)
NEON: 29999 usec.
ref: 41078 usec.
generic: 713206 usec.
checking NEON remap_stereo_to_mono(float)
NEON: 29114 usec.
ref: 237216 usec.
generic: 823254 usec.
checking NEON remap_mono_to_stereo(s16)
NEON: 15136 usec.
ref: 37690 usec.
generic: 128878 usec.
checking NEON remap_stereo_to_mono(s16)
NEON: 12024 usec.
ref: 49104 usec.
generic: 122439 usec.

---
 src/pulsecore/remap.c |   50 ++++++++++++++++++++++++++++++++++++++++++++++++-
 1 files changed, 49 insertions(+), 1 deletions(-)

diff --git a/src/pulsecore/remap.c b/src/pulsecore/remap.c
index b831f78..09257ab 100644
--- a/src/pulsecore/remap.c
+++ b/src/pulsecore/remap.c
@@ -85,6 +85,51 @@ static void remap_mono_to_stereo_c(pa_remap_t *m, void *dst, const void *src, un
     }
 }
 
+static void remap_stereo_to_mono_c(pa_remap_t *m, void *dst, const void *src, unsigned n) {
+    unsigned i;
+
+    switch (*m->format) {
+        case PA_SAMPLE_FLOAT32NE:
+        {
+            float *d = (float *) dst, *s = (float *) src;
+
+            for (i = n >> 2; i > 0; i--) {
+                d[0] = s[0] + s[1];
+                d[1] = s[2] + s[3];
+                d[2] = s[4] + s[5];
+                d[3] = s[6] + s[7];
+                s += 8;
+                d += 4;
+            }
+            for (i = n & 3; i; i--) {
+                d[0] = s[0] + s[1];
+                s += 2;
+                d += 1;
+            }
+            break;
+        }
+        case PA_SAMPLE_S16NE:
+        {
+            int16_t *d = (int16_t *) dst, *s = (int16_t *) src;
+
+            for (i = n >> 2; i > 0; i--) {
+                *d++ += s[0] + s[1];
+                *d++ += s[2] + s[3];
+                *d++ += s[4] + s[5];
+                *d++ += s[6] + s[7];
+                s += 8;
+            }
+            for (i = n & 3; i; i--) {
+                *d++ += s[0] + s[1];
+                s += 2;
+            }
+            break;
+        }
+        default:
+            pa_assert_not_reached();
+    }
+}
+
 static void remap_channels_matrix_c(pa_remap_t *m, void *dst, const void *src, unsigned n) {
     unsigned oc, ic, i;
     unsigned n_ic, n_oc;
@@ -171,13 +216,16 @@ static void init_remap_c(pa_remap_t *m) {
             m->map_table_f[0][0] >= 1.0 && m->map_table_f[1][0] >= 1.0) {
         m->do_remap = (pa_do_remap_func_t) remap_mono_to_stereo_c;
         pa_log_info("Using mono to stereo remapping");
+    } else if (n_ic == 2 && n_oc == 1 &&
+            m->map_table_f[0][0] >= 1.0 && m->map_table_f[0][1] >= 1.0) {
+        m->do_remap = (pa_do_remap_func_t) remap_stereo_to_mono_c;
+        pa_log_info("Using stereo to mono remapping");
     } else {
         m->do_remap = (pa_do_remap_func_t) remap_channels_matrix_c;
         pa_log_info("Using generic matrix remapping");
     }
 }
 
-
 /* default C implementation */
 static pa_init_remap_func_t remap_func = init_remap_c;
 
-- 
1.7.4.1