echo-cancel: Add function pa_echo_canceller_blocksize_power2()

computes EC block size in frames (rounded down to nearest power-of-2) based
on sample rate and milliseconds

move code from speex AEC implementation to module-echo-cancel such that
functionality can be reused by other AEC implementations

Signed-off-by: Peter Meerwald <p.meerwald@bct-electronic.com>

src/modules/echo-cancel/echo-cancel.h

@@ -131,6 +131,10 @@ struct pa_echo_canceller {
 void pa_echo_canceller_get_capture_volume(pa_echo_canceller *ec, pa_cvolume *v);
 void pa_echo_canceller_set_capture_volume(pa_echo_canceller *ec, pa_cvolume *v);
 
+/* Computes EC block size in frames (rounded down to nearest power-of-2) based
+ * on sample rate and milliseconds. */
+uint32_t pa_echo_canceller_blocksize_power2(unsigned rate, unsigned ms);
+
 /* Null canceller functions */
 pa_bool_t pa_null_ec_init(pa_core *c, pa_echo_canceller *ec,
                            pa_sample_spec *source_ss, pa_channel_map *source_map,

src/modules/echo-cancel/module-echo-cancel.c

@@ -1569,6 +1569,21 @@ void pa_echo_canceller_set_capture_volume(pa_echo_canceller *ec, pa_cvolume *v)
     }
 }
 
+uint32_t pa_echo_canceller_blocksize_power2(unsigned rate, unsigned ms) {
+    unsigned nframes = (rate * ms) / 1000;
+    uint32_t y = 1 << ((8 * sizeof(uint32_t)) - 2);
+
+    assert(rate >= 4000);
+    assert(ms >= 1);
+
+    /* nframes should be a power of 2, round down to nearest power of two */
+    while (y > nframes)
+        y >>= 1;
+
+    assert(y >= 1);
+    return y;
+}
+
 static pa_echo_canceller_method_t get_ec_method_from_string(const char *method) {
     if (pa_streq(method, "null"))
         return PA_ECHO_CANCELLER_NULL;

src/modules/echo-cancel/speex.c

@@ -151,7 +151,7 @@ pa_bool_t pa_speex_ec_init(pa_core *c, pa_echo_canceller *ec,
                            uint32_t *nframes, const char *args)
 {
     int rate;
-    uint32_t y, frame_size_ms, filter_size_ms;
+    uint32_t frame_size_ms, filter_size_ms;
     pa_modargs *ma;
 
     if (!(ma = pa_modargs_new(args, valid_modargs))) {
@@ -174,15 +174,9 @@ pa_bool_t pa_speex_ec_init(pa_core *c, pa_echo_canceller *ec,
     pa_speex_ec_fixate_spec(source_ss, source_map, sink_ss, sink_map);
 
     rate = source_ss->rate;
-    *nframes = (rate * frame_size_ms) / 1000;
+    *nframes = pa_echo_canceller_blocksize_power2(rate, frame_size_ms);
-    /* nframes should be a power of 2, round down to nearest power of two */
-    y = 1 << ((8 * sizeof (uint32_t)) - 2);
-    while (y > *nframes)
-      y >>= 1;
-    *nframes = y;
 
     pa_log_debug ("Using nframes %d, channels %d, rate %d", *nframes, source_ss->channels, source_ss->rate);
-
     ec->params.priv.speex.state = speex_echo_state_init_mc(*nframes, (rate * filter_size_ms) / 1000, source_ss->channels, source_ss->channels);
 
     if (!ec->params.priv.speex.state)