1 files changed, 106 insertions, 0 deletions
diff --git a/main/ulaw.c b/main/ulaw.c
new file mode 100644
index 000000000..2735f6cce
--- /dev/null
+++ b/main/ulaw.c
@@ -0,0 +1,106 @@
+/*
+ * Asterisk -- An open source telephony toolkit.
+ *
+ * Copyright (C) 1999 - 2005, Digium, Inc.
+ *
+ * Mark Spencer <markster@digium.com>
+ *
+ * See http://www.asterisk.org for more information about
+ * the Asterisk project. Please do not directly contact
+ * any of the maintainers of this project for assistance;
+ * the project provides a web site, mailing lists and IRC
+ * channels for your use.
+ *
+ * This program is free software, distributed under the terms of
+ * the GNU General Public License Version 2. See the LICENSE file
+ * at the top of the source tree.
+ */
+
+/*! \file
+ *
+ * \brief u-Law to Signed linear conversion
+ *
+ * \author Mark Spencer <markster@digium.com> 
+ */
+
+#include "asterisk.h"
+
+ASTERISK_FILE_VERSION(__FILE__, "$Revision$")
+
+#include "asterisk/ulaw.h"
+
+#define ZEROTRAP    /*!< turn on the trap as per the MIL-STD */
+#define BIAS 0x84   /*!< define the add-in bias for 16 bit samples */
+#define CLIP 32635
+
+unsigned char __ast_lin2mu[16384];
+short __ast_mulaw[256];
+
+
+static unsigned char linear2ulaw(short sample)
+{
+	static int exp_lut[256] = {
+		0,0,1,1,2,2,2,2,3,3,3,3,3,3,3,3,
+		4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,
+		5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,
+		5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,
+		6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,
+		6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,
+		6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,
+		6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,
+		7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
+		7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
+		7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
+		7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
+		7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
+		7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
+		7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
+		7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7 };
+	int sign, exponent, mantissa;
+	unsigned char ulawbyte;
+
+	/* Get the sample into sign-magnitude. */
+	sign = (sample >> 8) & 0x80;          /* set aside the sign */
+	if (sign != 0) 
+		sample = -sample;              /* get magnitude */
+	if (sample > CLIP)
+		sample = CLIP;             /* clip the magnitude */
+
+	/* Convert from 16 bit linear to ulaw. */
+	sample = sample + BIAS;
+	exponent = exp_lut[(sample >> 7) & 0xFF];
+	mantissa = (sample >> (exponent + 3)) & 0x0F;
+	ulawbyte = ~(sign | (exponent << 4) | mantissa);
+#ifdef ZEROTRAP
+	if (ulawbyte == 0)
+		ulawbyte = 0x02;   /* optional CCITT trap */
+#endif
+
+	return ulawbyte;
+}
+
+/*!
+ * \brief  Set up mu-law conversion table
+ */
+void ast_ulaw_init(void)
+{
+	int i;
+	for (i = 0; i < 256; i++) {
+		short mu, e, f, y;
+		static short etab[] = {0,132,396,924,1980,4092,8316,16764};
+
+		mu = 255 - i;
+		e = (mu & 0x70) / 16;
+		f = mu & 0x0f;
+		y = f * (1 << (e + 3));
+		y += etab[e];
+		if (mu & 0x80)
+			y = -y;
+		__ast_mulaw[i] = y;
+	}
+	/* set up the reverse (mu-law) conversion table */
+	for (i = -32768; i < 32768; i++) {
+		__ast_lin2mu[((unsigned short)i) >> 2] = linear2ulaw(i);
+	}
+}
+