1 /*

     2  * This routine converts from linear to ulaw

     3  * 29 September 1989

     4  *

     5  * Craig Reese: IDA/Supercomputing Research Center

     6  * Joe Campbell: Department of Defense

     7  *

     8  * References:

     9  * 1) CCITT Recommendation G.711  (very difficult to follow)

    10  * 2) "A New Digital Technique for Implementation of Any 

    11  *     Continuous PCM Companding Law," Villeret, Michel,

    12  *     et al. 1973 IEEE Int. Conf. on Communications, Vol 1,

    13  *     1973, pg. 11.12-11.17

    14  * 3) MIL-STD-188-113,"Interoperability and Performance Standards

    15  *     for Analog-to_Digital Conversion Techniques,"

    16  *     17 February 1987

    17  *

    18  * Input: Signed 16 bit linear sample

    19  * Output: 8 bit ulaw sample

    20  */

    21 

    22 #ifdef HAVE_CONFIG_H

    23 #include "config.h"

    24 #endif

    25 

    26 #include <glib.h>

    27 

    28 #undef ZEROTRAP                 /* turn on the trap as per the MIL-STD */

    29 #define BIAS 0x84               /* define the add-in bias for 16 bit samples */

    30 #define CLIP 32635

    31 

    32 void

    33 mulaw_encode (gint16 * in, guint8 * out, gint numsamples)

    34 {

    35   static gint16 exp_lut[256] = { 0, 0, 1, 1, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 3, 3,

    36     4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,

    37     5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5,

    38     5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5,

    39     6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,

    40     6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,

    41     6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,

    42     6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,

    43     7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,

    44     7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,

    45     7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,

    46     7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,

    47     7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,

    48     7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,

    49     7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,

    50     7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7

    51   };

    52   gint16 sign, exponent, mantissa, i;

    53   gint16 sample;

    54   guint8 ulawbyte;

    55 

    56   for (i = 0; i < numsamples; i++) {

    57     sample = in[i];

    58       /** get the sample into sign-magnitude **/

    59     sign = (sample >> 8) & 0x80;        /* set aside the sign */

    60     if (sign != 0) {

    61       sample = -sample;         /* get magnitude */

    62     }

    63     /* sample can be zero because we can overflow in the inversion,

    64      * checking against the unsigned version solves this */

    65     if (((guint16) sample) > CLIP)

    66       sample = CLIP;            /* clip the magnitude */

    67 

    68       /** convert from 16 bit linear to ulaw **/

    69     sample = sample + BIAS;

    70     exponent = exp_lut[(sample >> 7) & 0xFF];

    71     mantissa = (sample >> (exponent + 3)) & 0x0F;

    72     ulawbyte = ~(sign | (exponent << 4) | mantissa);

    73 #ifdef ZEROTRAP

    74     if (ulawbyte == 0)

    75       ulawbyte = 0x02;          /* optional CCITT trap */

    76 #endif

    77     out[i] = ulawbyte;

    78   }

    79 }

    80 

    81 /*

    82  * This routine converts from ulaw to 16 bit linear

    83  * 29 September 1989

    84  *

    85  * Craig Reese: IDA/Supercomputing Research Center

    86  *

    87  * References:

    88  * 1) CCITT Recommendation G.711  (very difficult to follow)

    89  * 2) MIL-STD-188-113,"Interoperability and Performance Standards

    90  *     for Analog-to_Digital Conversion Techniques,"

    91  *     17 February 1987

    92  *

    93  * Input: 8 bit ulaw sample

    94  * Output: signed 16 bit linear sample

    95  */

    96 

    97 void

    98 mulaw_decode (guint8 * in, gint16 * out, gint numsamples)

    99 {

   100   static gint16 exp_lut[8] = { 0, 132, 396, 924, 1980, 4092, 8316, 16764 };

   101   gint16 sign, exponent, mantissa;

   102   guint8 ulawbyte;

   103   gint16 linear, i;

   104 

   105   for (i = 0; i < numsamples; i++) {

   106     ulawbyte = in[i];

   107     ulawbyte = ~ulawbyte;

   108     sign = (ulawbyte & 0x80);

   109     exponent = (ulawbyte >> 4) & 0x07;

   110     mantissa = ulawbyte & 0x0F;

   111     linear = exp_lut[exponent] + (mantissa << (exponent + 3));

   112     if (sign != 0)

   113       linear = -linear;

   114     out[i] = linear;

   115   }

   116 }