audioconvert: add volume ops

Add volume helpers and use this for the monitor output ports so
that we can add volumes to the monitor output signal as well.

spa/plugins/audioconvert/volume-ops-c.c

@@ -0,0 +1,45 @@
+/* Spa
+ *
+ * Copyright © 2021 Wim Taymans
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS IN THE SOFTWARE.
+ */
+
+#include "volume-ops.h"
+
+void
+volume_f32_c(struct volume *vol, void * SPA_RESTRICT dst,
+		const void * SPA_RESTRICT src, float volume, uint32_t n_samples)
+{
+	uint32_t n;
+	float *d = (float*)dst;
+	const float *s = (const float*)src;
+
+	if (volume == VOLUME_MIN) {
+		memset(d, 0, n_samples * sizeof(float));
+	}
+	else if (volume == VOLUME_NORM) {
+		spa_memcpy(d, s, n_samples * sizeof(float));
+	}
+	else {
+		for (n = 0; n < n_samples; n++)
+			d[n] = s[n] * volume;
+	}
+}