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g711.cpp

/*
 * This source code is a product of Sun Microsystems, Inc. and is provided
 * for unrestricted use.  Users may copy or modify this source code without
 * charge.
 *
 * SUN SOURCE CODE IS PROVIDED AS IS WITH NO WARRANTIES OF ANY KIND INCLUDING
 * THE WARRANTIES OF DESIGN, MERCHANTIBILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE, OR ARISING FROM A COURSE OF DEALING, USAGE OR TRADE PRACTICE.
 *
 * Sun source code is provided with no support and without any obligation on
 * the part of Sun Microsystems, Inc. to assist in its use, correction,
 * modification or enhancement.
 *
 * SUN MICROSYSTEMS, INC. SHALL HAVE NO LIABILITY WITH RESPECT TO THE
 * INFRINGEMENT OF COPYRIGHTS, TRADE SECRETS OR ANY PATENTS BY THIS SOFTWARE
 * OR ANY PART THEREOF.
 *
 * In no event will Sun Microsystems, Inc. be liable for any lost revenue
 * or profits or other special, indirect and consequential damages, even if
 * Sun has been advised of the possibility of such damages.
 *
 * Sun Microsystems, Inc.
 * 2550 Garcia Avenue
 * Mountain View, California  94043
 */

#include "wx/wxprec.h"

/*
 * g711.c
 *
 * u-law, A-law and linear PCM conversions.
 */
#define     SIGN_BIT    (0x80)            /* Sign bit for a A-law byte. */
#define     QUANT_MASK  (0xf)       /* Quantization field mask. */
#define     NSEGS       (8)         /* Number of A-law segments. */
#define     SEG_SHIFT   (4)         /* Left shift for segment number. */
#define     SEG_MASK    (0x70)            /* Segment field mask. */

static short seg_end[8] = {0xFF, 0x1FF, 0x3FF, 0x7FF,
                      0xFFF, 0x1FFF, 0x3FFF, 0x7FFF};

/* copy from CCITT G.711 specifications */
unsigned char _u2a[128] = {               /* u- to A-law conversions */
      1,    1,    2,    2,    3,    3,    4,    4,
      5,    5,    6,    6,    7,    7,    8,    8,
      9,    10,   11,   12,   13,   14,   15,   16,
      17,   18,   19,   20,   21,   22,   23,   24,
      25,   27,   29,   31,   33,   34,   35,   36,
      37,   38,   39,   40,   41,   42,   43,   44,
      46,   48,   49,   50,   51,   52,   53,   54,
      55,   56,   57,   58,   59,   60,   61,   62,
      64,   65,   66,   67,   68,   69,   70,   71,
      72,   73,   74,   75,   76,   77,   78,   79,
      81,   82,   83,   84,   85,   86,   87,   88,
      89,   90,   91,   92,   93,   94,   95,   96,
      97,   98,   99,   100,  101,  102,  103,  104,
      105,  106,  107,  108,  109,  110,  111,  112,
      113,  114,  115,  116,  117,  118,  119,  120,
      121,  122,  123,  124,  125,  126,  127,  128};

unsigned char _a2u[128] = {               /* A- to u-law conversions */
      1,    3,    5,    7,    9,    11,   13,   15,
      16,   17,   18,   19,   20,   21,   22,   23,
      24,   25,   26,   27,   28,   29,   30,   31,
      32,   32,   33,   33,   34,   34,   35,   35,
      36,   37,   38,   39,   40,   41,   42,   43,
      44,   45,   46,   47,   48,   48,   49,   49,
      50,   51,   52,   53,   54,   55,   56,   57,
      58,   59,   60,   61,   62,   63,   64,   64,
      65,   66,   67,   68,   69,   70,   71,   72,
      73,   74,   75,   76,   77,   78,   79,   79,
      80,   81,   82,   83,   84,   85,   86,   87,
      88,   89,   90,   91,   92,   93,   94,   95,
      96,   97,   98,   99,   100,  101,  102,  103,
      104,  105,  106,  107,  108,  109,  110,  111,
      112,  113,  114,  115,  116,  117,  118,  119,
      120,  121,  122,  123,  124,  125,  126,  127};

static int
search(
      int         val,
      short       *table,
      int         size)
{
      int         i;

      for (i = 0; i < size; i++) {
            if (val <= *table++)
                  return (i);
      }
      return (size);
}

/*
 * linear2alaw() - Convert a 16-bit linear PCM value to 8-bit A-law
 *
 * linear2alaw() accepts an 16-bit integer and encodes it as A-law data.
 *
 *          Linear Input Code Compressed Code
 *    ------------------------      ---------------
 *    0000000wxyza                  000wxyz
 *    0000001wxyza                  001wxyz
 *    000001wxyzab                  010wxyz
 *    00001wxyzabc                  011wxyz
 *    0001wxyzabcd                  100wxyz
 *    001wxyzabcde                  101wxyz
 *    01wxyzabcdef                  110wxyz
 *    1wxyzabcdefg                  111wxyz
 *
 * For further information see John C. Bellamy's Digital Telephony, 1982,
 * John Wiley & Sons, pps 98-111 and 472-476.
 */
unsigned char
linear2alaw(
      int         pcm_val)    /* 2's complement (16-bit range) */
{
      int         mask;
      int         seg;
      unsigned char     aval;

      if (pcm_val >= 0) {
            mask = 0xD5;            /* sign (7th) bit = 1 */
      } else {
            mask = 0x55;            /* sign bit = 0 */
            pcm_val = -pcm_val - 8;
      }

      /* Convert the scaled magnitude to segment number. */
      seg = search(pcm_val, seg_end, 8);

      /* Combine the sign, segment, and quantization bits. */

      if (seg >= 8)           /* out of range, return maximum value. */
            return (0x7F ^ mask);
      else {
            aval = seg << SEG_SHIFT;
            if (seg < 2)
                  aval |= (pcm_val >> 4) & QUANT_MASK;
            else
                  aval |= (pcm_val >> (seg + 3)) & QUANT_MASK;
            return (aval ^ mask);
      }
}

/*
 * alaw2linear() - Convert an A-law value to 16-bit linear PCM
 *
 */
int
alaw2linear(
      unsigned char     a_val)
{
      int         t;
      int         seg;

      a_val ^= 0x55;

      t = (a_val & QUANT_MASK) << 4;
      seg = ((unsigned)a_val & SEG_MASK) >> SEG_SHIFT;
      switch (seg) {
      case 0:
            t += 8;
            break;
      case 1:
            t += 0x108;
            break;
      default:
            t += 0x108;
            t <<= seg - 1;
      }
      return ((a_val & SIGN_BIT) ? t : -t);
}

#define     BIAS        (0x84)            /* Bias for linear code. */

/*
 * linear2ulaw() - Convert a linear PCM value to u-law
 *
 * In order to simplify the encoding process, the original linear magnitude
 * is biased by adding 33 which shifts the encoding range from (0 - 8158) to
 * (33 - 8191). The result can be seen in the following encoding table:
 *
 *    Biased Linear Input Code      Compressed Code
 *    ------------------------      ---------------
 *    00000001wxyza                 000wxyz
 *    0000001wxyzab                 001wxyz
 *    000001wxyzabc                 010wxyz
 *    00001wxyzabcd                 011wxyz
 *    0001wxyzabcde                 100wxyz
 *    001wxyzabcdef                 101wxyz
 *    01wxyzabcdefg                 110wxyz
 *    1wxyzabcdefgh                 111wxyz
 *
 * Each biased linear code has a leading 1 which identifies the segment
 * number. The value of the segment number is equal to 7 minus the number
 * of leading 0's. The quantization interval is directly available as the
 * four bits wxyz.  * The trailing bits (a - h) are ignored.
 *
 * Ordinarily the complement of the resulting code word is used for
 * transmission, and so the code word is complemented before it is returned.
 *
 * For further information see John C. Bellamy's Digital Telephony, 1982,
 * John Wiley & Sons, pps 98-111 and 472-476.
 */
unsigned char
linear2ulaw(
      int         pcm_val)    /* 2's complement (16-bit range) */
{
      int         mask;
      int         seg;
      unsigned char     uval;

      /* Get the sign and the magnitude of the value. */
      if (pcm_val < 0) {
            pcm_val = BIAS - pcm_val;
            mask = 0x7F;
      } else {
            pcm_val += BIAS;
            mask = 0xFF;
      }

      /* Convert the scaled magnitude to segment number. */
      seg = search(pcm_val, seg_end, 8);

      /*
       * Combine the sign, segment, quantization bits;
       * and complement the code word.
       */
      if (seg >= 8)           /* out of range, return maximum value. */
            return (0x7F ^ mask);
      else {
            uval = (seg << 4) | ((pcm_val >> (seg + 3)) & 0xF);
            return (uval ^ mask);
      }

}

/*
 * ulaw2linear() - Convert a u-law value to 16-bit linear PCM
 *
 * First, a biased linear code is derived from the code word. An unbiased
 * output can then be obtained by subtracting 33 from the biased code.
 *
 * Note that this function expects to be passed the complement of the
 * original code word. This is in keeping with ISDN conventions.
 */
int
ulaw2linear(
      unsigned char     u_val)
{
      int         t;

      /* Complement to obtain normal u-law value. */
      u_val = ~u_val;

      /*
       * Extract and bias the quantization bits. Then
       * shift up by the segment number and subtract out the bias.
       */
      t = ((u_val & QUANT_MASK) << 3) + BIAS;
      t <<= ((unsigned)u_val & SEG_MASK) >> SEG_SHIFT;

      return ((u_val & SIGN_BIT) ? (BIAS - t) : (t - BIAS));
}

/* A-law to u-law conversion */
unsigned char
alaw2ulaw(
      unsigned char     aval)
{
      aval &= 0xff;
      return ((aval & 0x80) ? (0xFF ^ _a2u[aval ^ 0xD5]) :
          (0x7F ^ _a2u[aval ^ 0x55]));
}

/* u-law to A-law conversion */
unsigned char
ulaw2alaw(
      unsigned char     uval)
{
      uval &= 0xff;
      return ((uval & 0x80) ? (0xD5 ^ (_u2a[0xFF ^ uval] - 1)) :
          (0x55 ^ (_u2a[0x7F ^ uval] - 1)));
}

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