libaudiofile/g711.h

   1 /*
   2  * This source code is a product of Sun Microsystems, Inc. and is provided
   3  * for unrestricted use.  Users may copy or modify this source code without
   4  * charge.
   5  *
   6  * SUN SOURCE CODE IS PROVIDED AS IS WITH NO WARRANTIES OF ANY KIND INCLUDING
   7  * THE WARRANTIES OF DESIGN, MERCHANTIBILITY AND FITNESS FOR A PARTICULAR
   8  * PURPOSE, OR ARISING FROM A COURSE OF DEALING, USAGE OR TRADE PRACTICE.
   9  *
  10  * Sun source code is provided with no support and without any obligation on
  11  * the part of Sun Microsystems, Inc. to assist in its use, correction,
  12  * modification or enhancement.
  13  *
  14  * SUN MICROSYSTEMS, INC. SHALL HAVE NO LIABILITY WITH RESPECT TO THE
  15  * INFRINGEMENT OF COPYRIGHTS, TRADE SECRETS OR ANY PATENTS BY THIS SOFTWARE
  16  * OR ANY PART THEREOF.
  17  *
  18  * In no event will Sun Microsystems, Inc. be liable for any lost revenue
  19  * or profits or other special, indirect and consequential damages, even if
  20  * Sun has been advised of the possibility of such damages.
  21  *
  22  * Sun Microsystems, Inc.
  23  * 2550 Garcia Avenue
  24  * Mountain View, California  94043
  25  */
  26
  27 /*
  28  * g711.h
  29  *
  30  * u-law, A-law and linear PCM conversions.
  31  */
  32
  33 #ifndef G711_H
  34 #define G711_H
  35
  36 /*
  37  * linear2alaw() - Convert a 16-bit linear PCM value to 8-bit A-law
  38  *
  39  * linear2alaw() accepts an 16-bit integer and encodes it as A-law data.
  40  *
  41  *              Linear Input Code       Compressed Code
  42  *      ------------------------        ---------------
  43  *      0000000wxyza                    000wxyz
  44  *      0000001wxyza                    001wxyz
  45  *      000001wxyzab                    010wxyz
  46  *      00001wxyzabc                    011wxyz
  47  *      0001wxyzabcd                    100wxyz
  48  *      001wxyzabcde                    101wxyz
  49  *      01wxyzabcdef                    110wxyz
  50  *      1wxyzabcdefg                    111wxyz
  51  *
  52  * For further information see John C. Bellamy's Digital Telephony, 1982,
  53  * John Wiley & Sons, pps 98-111 and 472-476.
  54  */
  55
  56 /* pcm_val is 2's complement (16-bit range) */
  57 unsigned char _af_linear2alaw (int pcm_val);
  58
  59 /*
  60  * alaw2linear() - Convert an A-law value to 16-bit linear PCM
  61  *
  62  */
  63
  64 int _af_alaw2linear (unsigned char a_val);
  65
  66 /*
  67  * linear2ulaw() - Convert a linear PCM value to u-law
  68  *
  69  * In order to simplify the encoding process, the original linear magnitude
  70  * is biased by adding 33 which shifts the encoding range from (0 - 8158) to
  71  * (33 - 8191). The result can be seen in the following encoding table:
  72  *
  73  *      Biased Linear Input Code        Compressed Code
  74  *      ------------------------        ---------------
  75  *      00000001wxyza                   000wxyz
  76  *      0000001wxyzab                   001wxyz
  77  *      000001wxyzabc                   010wxyz
  78  *      00001wxyzabcd                   011wxyz
  79  *      0001wxyzabcde                   100wxyz
  80  *      001wxyzabcdef                   101wxyz
  81  *      01wxyzabcdefg                   110wxyz
  82  *      1wxyzabcdefgh                   111wxyz
  83  *
  84  * Each biased linear code has a leading 1 which identifies the segment
  85  * number. The value of the segment number is equal to 7 minus the number
  86  * of leading 0's. The quantization interval is directly available as the
  87  * four bits wxyz.  * The trailing bits (a - h) are ignored.
  88  *
  89  * Ordinarily the complement of the resulting code word is used for
  90  * transmission, and so the code word is complemented before it is returned.
  91  *
  92  * For further information see John C. Bellamy's Digital Telephony, 1982,
  93  * John Wiley & Sons, pps 98-111 and 472-476.
  94  */
  95
  96 /* pcm_val is 2's complement (16-bit range) */
  97 unsigned char _af_linear2ulaw (int pcm_val);
  98
  99 /*
 100  * ulaw2linear() - Convert a u-law value to 16-bit linear PCM
 101  *
 102  * First, a biased linear code is derived from the code word. An unbiased
 103  * output can then be obtained by subtracting 33 from the biased code.
 104  *
 105  * Note that this function expects to be passed the complement of the
 106  * original code word. This is in keeping with ISDN conventions.
 107  */
 108
 109 int _af_ulaw2linear (unsigned char u_val);
 110
 111 #endif /* G711_H */