merge robin gareus' libltc into ardour source tree for convenience

git-svn-id: svn://localhost/ardour2/branches/3.0@13665 d708f5d6-7413-0410-9779-e7cbd77b26cf

1 files changed, 106 insertions, 0 deletions

diff --git a/libs/libltc/encoder.c b/libs/libltc/encoder.c
new file mode 100644
index 0000000000..fce2a0ce51
--- /dev/null
+++ b/libs/libltc/encoder.c
@@ -0,0 +1,106 @@
+/*
+   libltc - en+decode linear timecode
+
+   Copyright (C) 2006-2012 Robin Gareus <robin@gareus.org>
+
+   This program 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 3 of the
+   License, or (at your option) any later version.
+
+   This program 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 Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with this library.
+   If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <math.h>
+
+#include "ltc/encoder.h"
+
+/**
+ * add values to the output buffer
+ */
+static int addvalues(LTCEncoder *e, int n) {
+	const ltcsnd_sample_t tgtval = e->state ? e->enc_hi : e->enc_lo;
+
+	if (e->offset + n >= e->bufsize) {
+		fprintf(stderr, "libltc: buffer overflow: %d/%lu\n", (int) e->offset, (unsigned long) e->bufsize);
+		return 1;
+	}
+
+	ltcsnd_sample_t * const wave = &(e->buf[e->offset]);
+	const double tcf =  e->filter_const;
+	if (tcf > 0) {
+		/* low-pass-filter
+		 * LTC signal should have a rise time of 40 us +/- 10 us.
+		 *
+		 * rise-time means from <10% to >90% of the signal.
+		 * in each call to addvalues() we start at 50%, so
+		 * here we need half-of it. (0.000020 sec)
+		 *
+		 * e->cutoff = 1.0 -exp( -1.0 / (sample_rate * .000020 / exp(1.0)) );
+		 */
+		int i;
+		ltcsnd_sample_t val = SAMPLE_CENTER;
+		int m = (n+1)>>1;
+		for (i = 0 ; i < m ; i++) {
+			val = val + tcf * (tgtval - val);
+			wave[n-i-1] = wave[i] = val;
+		}
+	} else {
+		/* perfect square wave */
+		memset(wave, tgtval, n);
+	}
+
+	e->offset += n;
+	return 0;
+}
+
+int encode_byte(LTCEncoder *e, int byte, double speed) {
+	if (byte < 0 || byte > 9) return -1;
+	if (speed ==0) return -1;
+
+	int err = 0;
+	const unsigned char c = ((unsigned char*)&e->f)[byte];
+	unsigned char b = (speed < 0)?128:1; // bit
+	const double spc = e->samples_per_clock * fabs(speed);
+	const double sph = e->samples_per_clock_2 * fabs(speed);
+
+	do
+	{
+		int n;
+		if ((c & b) == 0) {
+			n = (int)(spc + e->sample_remainder);
+			e->sample_remainder = spc + e->sample_remainder - n;
+			e->state = !e->state;
+			err |= addvalues(e, n);
+		} else {
+			n = (int)(sph + e->sample_remainder);
+			e->sample_remainder = sph + e->sample_remainder - n;
+			e->state = !e->state;
+			err |= addvalues(e, n);
+
+			n = (int)(sph + e->sample_remainder);
+			e->sample_remainder = sph + e->sample_remainder - n;
+			e->state = !e->state;
+			err |= addvalues(e, n);
+		}
+		/* this is based on the assumption that with every compiler
+		 * ((unsigned char) 128)<<1 == ((unsigned char 1)>>1) == 0
+		 */
+		if (speed < 0)
+			b >>= 1;
+		else
+			b <<= 1;
+	} while (b);
+
+	return err;
+}