Added libsoxr resampler backend.

The new backend supports 3 quality levels: mq, hq and vhq; 16-bit integer and 32-bit float samples. Discussion and quality assessment are here:

http://comments.gmane.org/gmane.comp.audio.pulseaudio.general/22158

src/pulsecore/resampler/soxr.c

@@ -0,0 +1,167 @@
+/***
+  This file is part of PulseAudio.
+
+  Copyright 2014, 2015 Andrey Semashev
+
+  PulseAudio is free software; you can redistribute it and/or modify
+  it under the terms of the GNU Lesser General Public License as published
+  by the Free Software Foundation; either version 2.1 of the License,
+  or (at your option) any later version.
+
+  PulseAudio is distributed in the hope that it will be useful, but
+  WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+  General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public License
+  along with PulseAudio; if not, see <http://www.gnu.org/licenses/>.
+***/
+
+#ifdef HAVE_CONFIG_H
+#include <config.h>
+#endif
+
+#include <stddef.h>
+#include <soxr.h>
+
+#include <pulsecore/resampler.h>
+
+static unsigned resampler_soxr_resample(pa_resampler *r, const pa_memchunk *input, unsigned in_n_frames,
+                                        pa_memchunk *output, unsigned *out_n_frames) {
+    soxr_t state;
+    void *in, *out;
+    size_t consumed = 0, produced = 0;
+
+    pa_assert(r);
+    pa_assert(input);
+    pa_assert(output);
+    pa_assert(out_n_frames);
+
+    state = r->impl.data;
+    pa_assert(state);
+
+    in = pa_memblock_acquire_chunk(input);
+    out = pa_memblock_acquire_chunk(output);
+
+    pa_assert_se(soxr_process(state, in, in_n_frames, &consumed, out, *out_n_frames, &produced) == 0);
+
+    pa_memblock_release(input->memblock);
+    pa_memblock_release(output->memblock);
+
+    *out_n_frames = produced;
+
+    return in_n_frames - consumed;
+}
+
+static void resampler_soxr_free(pa_resampler *r) {
+    pa_assert(r);
+
+    if (!r->impl.data)
+        return;
+
+    soxr_delete(r->impl.data);
+    r->impl.data = NULL;
+}
+
+static void resampler_soxr_reset(pa_resampler *r) {
+    soxr_t old_state;
+
+    pa_assert(r);
+
+    /*
+     * soxr_clear() makes soxr_process() crash afterwards,
+     * so don't use this function until libsoxr is fixed.
+     *
+     * soxr_clear(r->impl.data);
+     */
+
+    old_state = r->impl.data;
+    r->impl.data = NULL;
+
+    if (pa_resampler_soxr_init(r) == 0) {
+        if (old_state)
+            soxr_delete(old_state);
+    } else {
+        r->impl.data = old_state;
+        pa_log_error("Failed to reset libsoxr context");
+    }
+}
+
+static void resampler_soxr_update_rates(pa_resampler *r) {
+    soxr_t old_state;
+
+    pa_assert(r);
+
+    /* There is no update method in libsoxr,
+     * so just re-create the resampler context */
+
+    old_state = r->impl.data;
+    r->impl.data = NULL;
+
+    if (pa_resampler_soxr_init(r) == 0) {
+        if (old_state)
+            soxr_delete(old_state);
+    } else {
+        r->impl.data = old_state;
+        pa_log_error("Failed to update libsoxr sample rates");
+    }
+}
+
+int pa_resampler_soxr_init(pa_resampler *r) {
+    soxr_t state;
+    soxr_datatype_t io_format;
+    soxr_io_spec_t io_spec;
+    soxr_runtime_spec_t runtime_spec;
+    unsigned long quality_recipe;
+    soxr_quality_spec_t quality;
+    soxr_error_t err = NULL;
+
+    pa_assert(r);
+
+    switch (r->work_format) {
+        case PA_SAMPLE_S16NE:
+            io_format = SOXR_INT16_I;
+            break;
+        case PA_SAMPLE_FLOAT32NE:
+            io_format = SOXR_FLOAT32_I;
+            break;
+        default:
+            pa_assert_not_reached();
+    }
+
+    io_spec = soxr_io_spec(io_format, io_format);
+
+    /* Resample in one thread. Multithreading makes
+     * performance worse with small chunks of audio. */
+    runtime_spec = soxr_runtime_spec(1);
+
+    switch (r->method) {
+        case PA_RESAMPLER_SOXR_MQ:
+            quality_recipe = SOXR_MQ | SOXR_LINEAR_PHASE;
+            break;
+        case PA_RESAMPLER_SOXR_HQ:
+            quality_recipe = SOXR_HQ | SOXR_LINEAR_PHASE;
+            break;
+        case PA_RESAMPLER_SOXR_VHQ:
+            quality_recipe = SOXR_VHQ | SOXR_LINEAR_PHASE;
+            break;
+        default:
+            pa_assert_not_reached();
+    }
+
+    quality = soxr_quality_spec(quality_recipe, 0);
+
+    state = soxr_create(r->i_ss.rate, r->o_ss.rate, r->work_channels, &err, &io_spec, &quality, &runtime_spec);
+    if (!state) {
+        pa_log_error("Failed to create libsoxr resampler context: %s.", (err ? err : "[unknown error]"));
+        return -1;
+    }
+
+    r->impl.free = resampler_soxr_free;
+    r->impl.reset = resampler_soxr_reset;
+    r->impl.update_rates = resampler_soxr_update_rates;
+    r->impl.resample = resampler_soxr_resample;
+    r->impl.data = state;
+
+    return 0;
+}