88 lines
2.3 KiB
C
88 lines
2.3 KiB
C
/*
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* Asterisk -- An open source telephony toolkit.
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*
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* Copyright (C) 1999 - 2005, Digium, Inc.
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*
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* Mark Spencer <markster@digium.com>
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*
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* See http://www.asterisk.org for more information about
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* the Asterisk project. Please do not directly contact
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* any of the maintainers of this project for assistance;
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* the project provides a web site, mailing lists and IRC
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* channels for your use.
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*
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* This program is free software, distributed under the terms of
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* the GNU General Public License Version 2. See the LICENSE file
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* at the top of the source tree.
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*/
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/*! \file
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* \brief u-Law to Signed linear conversion
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*/
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#ifndef _ASTERISK_ULAW_H
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#define _ASTERISK_ULAW_H
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/*!
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* To init the ulaw to slinear conversion stuff, this needs to be run.
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*/
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void ast_ulaw_init(void);
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#define AST_ULAW_BIT_LOSS 3
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#define AST_ULAW_STEP (1 << AST_ULAW_BIT_LOSS)
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#define AST_ULAW_TAB_SIZE (32768 / AST_ULAW_STEP + 1)
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#define AST_ULAW_SIGN_BIT 0x80
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/*! \brief converts signed linear to mulaw */
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#ifndef G711_NEW_ALGORITHM
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extern unsigned char __ast_lin2mu[16384];
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#else
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extern unsigned char __ast_lin2mu[AST_ULAW_TAB_SIZE];
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#endif
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/*! help */
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extern short __ast_mulaw[256];
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#ifndef G711_NEW_ALGORITHM
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#define AST_LIN2MU(a) (__ast_lin2mu[((unsigned short)(a)) >> 2])
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#else
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#define AST_LIN2MU_LOOKUP(mag) \
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__ast_lin2mu[((mag) + AST_ULAW_STEP / 2) >> AST_ULAW_BIT_LOSS]
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/*! \brief convert signed linear sample to sign-magnitude pair for u-Law */
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static inline void ast_ulaw_get_sign_mag(short sample, unsigned *sign, unsigned *mag)
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{
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/* It may look illogical to retrive the sign this way in both cases,
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* but this helps gcc eliminate the branch below and produces
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* faster code */
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*sign = ((unsigned short)sample >> 8) & AST_ULAW_SIGN_BIT;
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#if defined(G711_REDUCED_BRANCHING)
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{
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unsigned dual_mag = (-sample << 16) | (unsigned short)sample;
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*mag = (dual_mag >> (*sign >> 3)) & 0xffffU;
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}
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#else
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if (sample < 0)
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*mag = -sample;
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else
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*mag = sample;
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#endif /* G711_REDUCED_BRANCHING */
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}
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static inline unsigned char AST_LIN2MU(short sample)
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{
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unsigned mag, sign;
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ast_ulaw_get_sign_mag(sample, &sign, &mag);
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return ~(sign | AST_LIN2MU_LOOKUP(mag));
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}
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#endif
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#define AST_MULAW(a) (__ast_mulaw[(a)])
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#endif /* _ASTERISK_ULAW_H */
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