audioutils: Add RTTTL parsing library

audioutils/rtttl-c/.gitignore

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+/rtttl-c

audioutils/rtttl-c/Kconfig

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+config AUDIOUTILS_RTTTL_C
+	bool "RTTTL parsing library"
+	default n
+	---help---
+		Simple library for parsing Ring Tone Text Transfer Language (RTTTL)
+
+		Define what to do with a tone:
+
+			void
+			play_tone(struct rtttl_tone tone)
+			{
+				/* TODO */
+			}
+
+		and then play RTTTL string:
+
+			rtttl_play("...", play_tone);

audioutils/rtttl-c/Make.defs

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+############################################################################
+# apps/audioutils/rtttl-c/Make.defs
+#
+# SPDX-License-Identifier: Apache-2.0
+#
+# Licensed to the Apache Software Foundation (ASF) under one or more
+# contributor license agreements.  See the NOTICE file distributed with
+# this work for additional information regarding copyright ownership.  The
+# ASF licenses this file to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance with the
+# License.  You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
+# License for the specific language governing permissions and limitations
+# under the License.
+#
+############################################################################
+
+ifneq ($(CONFIG_AUDIOUTILS_RTTTL_C),)
+CONFIGURED_APPS += $(APPDIR)/audioutils/rtttl-c
+endif

audioutils/rtttl-c/Makefile

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+############################################################################
+# apps/audioutils/rtttl-c/Makefile
+#
+# SPDX-License-Identifier: Apache-2.0
+#
+# Licensed to the Apache Software Foundation (ASF) under one or more
+# contributor license agreements.  See the NOTICE file distributed with
+# this work for additional information regarding copyright ownership.  The
+# ASF licenses this file to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance with the
+# License.  You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
+# License for the specific language governing permissions and limitations
+# under the License.
+#
+############################################################################
+
+include $(APPDIR)/Make.defs
+
+CSRCS = rtttl.c
+
+create_includes: rtttl.h
+	$(Q) cp $< $(APPDIR)/include/audioutils
+
+context::
+	$(Q) $(MAKE) create_includes
+
+distclean::
+	$(call DELFILE, $(APPDIR)/include/audioutils/rtttl.h)
+
+include $(APPDIR)/Application.mk

audioutils/rtttl-c/rtttl.c

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+/*
+ * SPDX-FileCopyrightText: 2026 Jiri Vlasak
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ * SPDX-License-Identifier: MIT
+ */
+
+#include "rtttl.h"
+
+static int
+is_allowed_in_part1(char c)
+{
+	return ':' != c && ' ' <= c && c < 0x7f;
+}
+
+static int
+isnum(char c)
+{
+	return '0' <= c && c <= '9';
+}
+
+static int
+getnum(char const **p)
+{
+	int num = (int)(**p - '0');
+	(*p)++;
+
+	while (isnum(**p)) {
+		num *= 10;
+		num += (int)(**p - '0');
+		(*p)++;
+	}
+
+	return num;
+}
+
+static int
+is_duration(int n)
+{
+	return 1 == n || 2 == n || 4 == n || 8 == n || 16 == n || 32 == n;
+}
+
+static int
+is_octave(int n)
+{
+	return 4 == n || 5 == n || 6 == n || 7 == n;
+}
+
+static void
+skip_spaces(char const **p)
+{
+	while (' ' == **p || '\t' == **p) {
+		(*p)++;
+	}
+}
+
+struct rtttl_conf
+rtttl_parse_conf(char const *rtttl_string)
+{
+	char const *p = rtttl_string;
+	int num;
+	struct rtttl_conf conf = {
+		.error = 0,
+		.duration = 4,
+		.octave = 6,
+		.beat = 63,
+	};
+
+	/* Skip part 1 */
+
+	while (is_allowed_in_part1(*p)) {
+		p++;
+	}
+	p++;
+
+	/* Parse part 2 */
+
+	while (':' != *p && '\0' != *p) {
+		skip_spaces(&p); /* Not by specification, but hey. */
+
+		switch (*p) {
+		case 'd':
+			p++;
+			if ('=' != *p) {
+				conf.error = -2;
+			}
+			p++;
+			num = -1;
+			if (isnum(*p)) {
+				num = getnum(&p);
+			} else {
+				conf.error = -3;
+			}
+			if (is_duration(num)) {
+				conf.duration = num;
+			} else {
+				conf.error = -4;
+			}
+			break;
+		case 'o':
+			p++;
+			if ('=' != *p) {
+				conf.error = -2;
+			}
+			p++;
+			num = -1;
+			if (isnum(*p)) {
+				num = getnum(&p);
+			} else {
+				conf.error = -5;
+			}
+			if (is_octave(num)) {
+				conf.octave = num;
+			} else {
+				conf.error = -6;
+			}
+			break;
+		case 'b':
+			p++;
+			if ('=' != *p) {
+				conf.error = -2;
+			}
+			p++;
+			num = -1;
+			if (isnum(*p)) {
+				conf.beat = getnum(&p);
+			} else {
+				conf.error = -7;
+			}
+			break;
+		default:
+			conf.error = -2;
+		}
+		if (',' == *p) {
+			p++;
+		}
+	}
+
+	return conf;
+}
+
+static int
+tone_frequency(char const **p)
+{
+	/* See https://muted.io/note-frequencies/ */
+
+	char tone = **p;
+	(*p)++;
+	int hash = **p == '#';
+
+	if (hash) {
+		(*p)++;
+	}
+
+	switch (tone) {
+	case 'p':
+	case 'P':
+		return 0;
+	case 'c':
+	case 'C':
+		return hash ? 27718 : 26163;
+	case 'd':
+	case 'D':
+		return hash ? 31113 : 29366;
+	case 'e':
+	case 'E':
+		return hash ? 34923 : 32963;
+	case 'f':
+	case 'F':
+		return hash ? 36999 : 34923;
+	case 'g':
+	case 'G':
+		return hash ? 41530 : 39200;
+	case 'a':
+	case 'A':
+		return hash ? 46616 : 44000;
+	case 'b':
+	case 'B':
+		return hash ? 52325 : 49388;
+	}
+	return -8;
+}
+
+int
+rtttl_play(char const *rtttl_string, void (*make_tone)(struct rtttl_tone))
+{
+	struct rtttl_conf conf = rtttl_parse_conf(rtttl_string);
+	if (0 != conf.error) {
+		return conf.error;
+	}
+
+	int num;
+	struct rtttl_tone tone;
+	char const *p = rtttl_string;
+
+	/* Skip part 1 */
+
+	while (is_allowed_in_part1(*p)) {
+		p++;
+	}
+	p++;
+
+	/* Skip part 2 */
+
+	while (':' != *p && '\0' != *p) {
+		p++;
+	}
+	p++;
+
+	/* Play part 3 */
+
+	while ('\0' != *p) {
+		skip_spaces(&p); /* Not by specification, but hey. */
+
+		tone.duration_us = 60 * 1000000;
+		tone.duration_us /= conf.beat;
+		tone.duration_us *= 4; /* Usually quarter notes per minute. */
+		num = -1;
+		if (isnum(*p)) {
+			num = getnum(&p);
+		}
+		if (!is_duration(num)) {
+			num = conf.duration;
+		}
+		tone.duration_us /= num;
+
+		tone.frequency_100hz = tone_frequency(&p);
+		if (0 > tone.frequency_100hz) {
+			return tone.frequency_100hz;
+		}
+
+		/* People sometimes write dot here. Why? */
+		if ('.' == *p) {
+			tone.duration_us >>= 1;
+			tone.duration_us *= 3;
+			p++;
+		}
+
+		num = -1;
+		if (isnum(*p)) {
+			num = getnum(&p);
+		}
+		if (!is_octave(num)) {
+			num = conf.octave;
+		}
+		tone.frequency_100hz <<= (num - 4); /* Double frequency? */
+
+		/* Frequency is returned in *100 Hz due to scaling. */
+		if (0 != tone.frequency_100hz) {
+			tone.period_us = 100 * 1000000 / tone.frequency_100hz;
+		} else {
+			tone.period_us = 0; /* Pause. */
+		}
+
+		/* People should put dot here if they want to. */
+		if ('.' == *p) {
+			tone.duration_us >>= 1;
+			tone.duration_us *= 3;
+			p++;
+		}
+
+		make_tone(tone);
+
+		if (',' == *p) {
+			p++;
+		} else if ('\0' != *p) {
+			return -9;
+		}
+	}
+	return 0;
+}