g711.cpp

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/*
 * 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)));
}