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/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;