1 files changed, 86 insertions, 0 deletions
diff --git a/trunk/include/asterisk/alaw.h b/trunk/include/asterisk/alaw.h
new file mode 100644
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+++ b/trunk/include/asterisk/alaw.h
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+/*
+ * 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 A-Law to Signed linear conversion
+ */
+
+#ifndef _ASTERISK_ALAW_H
+#define _ASTERISK_ALAW_H
+
+
+/*! \brief
+ * To init the alaw to slinear conversion stuff, this needs to be run.
+ */
+void ast_alaw_init(void);
+
+#define AST_ALAW_BIT_LOSS  4
+#define AST_ALAW_STEP      (1 << AST_ALAW_BIT_LOSS)
+#define AST_ALAW_TAB_SIZE  (32768 / AST_ALAW_STEP + 1)
+#define AST_ALAW_SIGN_BIT  0x80
+#define AST_ALAW_AMI_MASK  0x55
+
+
+/*! \brief converts signed linear to alaw */
+#ifndef G711_NEW_ALGORITHM
+extern unsigned char __ast_lin2a[8192];
+#else
+extern unsigned char __ast_lin2a[AST_ALAW_TAB_SIZE];
+#endif
+
+/*! help */
+extern short __ast_alaw[256];
+
+#ifndef G711_NEW_ALGORITHM
+#define AST_LIN2A(a) (__ast_lin2a[((unsigned short)(a)) >> 3])
+#else
+#define AST_LIN2A_LOOKUP(mag)							\
+	__ast_lin2a[(mag) >> AST_ALAW_BIT_LOSS]
+
+/*! \brief Convert signed linear sample to sign-magnitude pair for a-Law */
+static inline void ast_alaw_get_sign_mag(short sample, unsigned *sign, unsigned *mag)
+{
+	/* It may look illogical to retrive the sign this way in both cases,
+	 * but this helps gcc eliminate the branch below and produces
+	 * faster code */
+	*sign = ((unsigned short)sample >> 8) & AST_ALAW_SIGN_BIT;
+#if defined(G711_REDUCED_BRANCHING)
+	{
+		unsigned dual_mag = (-sample << 16) | (unsigned short)sample;
+		*mag = (dual_mag >> (*sign >> 3)) & 0xffffU;
+	}
+#else
+	if (sample < 0)
+		*mag = -sample;
+	else
+		*mag = sample;
+#endif /* G711_REDUCED_BRANCHING */
+	*sign ^= AST_ALAW_SIGN_BIT;
+}
+
+static inline unsigned char AST_LIN2A(short sample)
+{
+	unsigned mag, sign;
+	ast_alaw_get_sign_mag(sample, &sign, &mag);
+	return (sign | AST_LIN2A_LOOKUP(mag)) ^ AST_ALAW_AMI_MASK;
+}
+#endif
+
+#define AST_ALAW(a) (__ast_alaw[(int)(a)])
+
+#endif /* _ASTERISK_ALAW_H */