simple mixer: make output scalers O: optional and use default values instead

Reduces FLASH usage by about 4KB

Command to replace:
for i in *.mix; do sed -r -i '/O: +10000 +10000 +0 +-10000 +10000/d' $i; done

src/lib/mixer/mixer.cpp

@@ -40,6 +40,7 @@
 #include "mixer.h"
 
 #include <cstring>
+#include <ctype.h>
 
 #define debug(fmt, args...)	do { } while(0)
 //#define debug(fmt, args...)	do { printf("[mixer] " fmt "\n", ##args); } while(0)
@@ -125,6 +126,21 @@ Mixer::findtag(const char *buf, unsigned &buflen, char tag)
 	return nullptr;
 }
 
+char
+Mixer::findnexttag(const char *buf, unsigned buflen)
+{
+	while (buflen >= 2) {
+		if (isupper(buf[0]) && buf[1] == ':') {
+			return buf[0];
+		}
+
+		buf++;
+		buflen--;
+	}
+
+	return 0;
+}
+
 const char *
 Mixer::skipline(const char *buf, unsigned &buflen)
 {

src/lib/mixer/mixer.h

@@ -265,6 +265,14 @@ protected:
 	 */
 	static const char 		*findtag(const char *buf, unsigned &buflen, char tag);
 
+	/**
+	 * Find next tag and return it (0 is returned if no tag is found)
+	 *
+	 * @param buf			The buffer to operate on.
+	 * @param buflen		length of the buffer.
+	 */
+	static char 			findnexttag(const char *buf, unsigned buflen);
+
 	/**
 	 * Skip a line
 	 *
@@ -340,6 +348,7 @@ public:
 	 *   M: <control count>
 	 *   O: <-ve scale> <+ve scale> <offset> <lower limit> <upper limit>
 	 *
+	 * The second line O: can be omitted. In that case 'O: 10000 10000 0 -10000 10000' is used.
 	 * The definition continues with <control count> entries describing the control
 	 * inputs and their scaling, in the form:
 	 *

src/lib/mixer/mixer_simple.cpp

@@ -151,6 +151,7 @@ SimpleMixer::from_text(Mixer::ControlCallback control_cb, uintptr_t cb_handle, c
 	unsigned inputs;
 	int used;
 	const char *end = buf + buflen;
+	char next_tag;
 
 	/* enforce that the mixer ends with a new line */
 	if (!string_well_formed(buf, buflen)) {
@@ -163,6 +164,12 @@ SimpleMixer::from_text(Mixer::ControlCallback control_cb, uintptr_t cb_handle, c
 		goto out;
 	}
 
+	/* at least 1 input is required */
+	if (inputs == 0) {
+		debug("simple parse got 0 inputs");
+		goto out;
+	}
+
 	buf = skipline(buf, buflen);
 
 	if (buf == nullptr) {
@@ -179,9 +186,27 @@ SimpleMixer::from_text(Mixer::ControlCallback control_cb, uintptr_t cb_handle, c
 
 	mixinfo->control_count = inputs;
 
-	if (parse_output_scaler(end - buflen, buflen, mixinfo->output_scaler)) {
-		debug("simple mixer parser failed parsing out scaler tag, ret: '%s'", buf);
-		goto out;
+	/* find the next tag */
+	next_tag = findnexttag(end - buflen, buflen);
+
+	if (next_tag == 'S') {
+
+		/* No output scalers specified. Use default values.
+		 * Corresponds to:
+		 * O:      10000  10000      0 -10000  10000
+		 */
+		mixinfo->output_scaler.negative_scale	= 1.0f;
+		mixinfo->output_scaler.positive_scale	= 1.0f;
+		mixinfo->output_scaler.offset		= 0.f;
+		mixinfo->output_scaler.min_output	= -1.0f;
+		mixinfo->output_scaler.max_output	= 1.0f;
+
+	} else {
+
+		if (parse_output_scaler(end - buflen, buflen, mixinfo->output_scaler)) {
+			debug("simple mixer parser failed parsing out scaler tag, ret: '%s'", buf);
+			goto out;
+		}
 	}
 
 	for (unsigned i = 0; i < inputs; i++) {