D:/Storage/CVS_Head/h323plus/src/g711.c

/*
 * 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
 */

/*
 * g711.c
 *
 * u-law, A-law and linear PCM conversions.
 */

/*
 * December 30, 1994:
 * Functions linear2alaw, linear2ulaw have been updated to correctly
 * convert unquantized 16 bit values.
 * Tables for direct u- to A-law and A- to u-law conversions have been
 * corrected.
 * Borge Lindberg, Center for PersonKommunikation, Aalborg University.
 * bli@cpk.auc.dk
 *
 */
 
#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 int seg_aend[8] = {0x1F, 0x3F, 0x7F, 0xFF,
                            0x1FF, 0x3FF, 0x7FF, 0xFFF};
static int seg_uend[8] = {0x3F, 0x7F, 0xFF, 0x1FF,
                            0x3FF, 0x7FF, 0xFFF, 0x1FFF};

/* 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,
/* corrected:
        81,     82,     83,     84,     85,     86,     87,     88, 
   should be: */
        80,     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,
/* corrected:
        73,     74,     75,     76,     77,     78,     79,     79,
   should be: */
        73,     74,     75,     76,     77,     78,     79,     80,

        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,    /* changed from "short" *drago* */
        int *   table,
        int             size)   /* changed from "short" *drago* */
{
        int             i;              /* changed from "short" *drago* */

        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.
 */
int linear2alaw(int     pcm_val)        /* 2's complement (16-bit range) */
                                        /* changed from "short" *drago* */
{
        int             mask;   /* changed from "short" *drago* */
        int             seg;    /* changed from "short" *drago* */
        int             aval;

        pcm_val = pcm_val >> 3;

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

        /* Convert the scaled magnitude to segment number. */
        seg = search(pcm_val, seg_aend, 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 >> 1) & QUANT_MASK;
                else
                        aval |= (pcm_val >> seg) & QUANT_MASK;
                return (aval ^ mask);
        }
}

/*
 * alaw2linear() - Convert an A-law value to 16-bit linear PCM
 *
 */
int alaw2linear(int     a_val)          
{
        int             t;      /* changed from "short" *drago* */
        int             seg;    /* changed from "short" *drago* */

        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. */
#define CLIP            8159

/*
 * 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.
 */
int linear2ulaw( int    pcm_val)        /* 2's complement (16-bit range) */
{
        int             mask;
        int             seg;
        int             uval;

        /* Get the sign and the magnitude of the value. */
        pcm_val = pcm_val >> 2;
        if (pcm_val < 0) {
                pcm_val = -pcm_val;
                mask = 0x7F;
        } else {
                mask = 0xFF;
        }
        if ( pcm_val > CLIP ) pcm_val = CLIP;           /* clip the magnitude */
        pcm_val += (BIAS >> 2);

        /* Convert the scaled magnitude to segment number. */
        seg = search(pcm_val, seg_uend, 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 + 1)) & 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( int    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 <<= (u_val & SEG_MASK) >> SEG_SHIFT;

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

#if 0

/* A-law to u-law conversion */
static int alaw2ulaw (int       aval)
{
        aval &= 0xff;
        return ((aval & 0x80) ? (0xFF ^ a2u[aval ^ 0xD5]) :
            (0x7F ^ a2u[aval ^ 0x55]));
}

/* u-law to A-law conversion */
static int ulaw2alaw (int       uval)
{
        uval &= 0xff;
        return ((uval & 0x80) ? (0xD5 ^ (u2a[0xFF ^ uval] - 1)) :
            (0x55 ^ (u2a[0x7F ^ uval] - 1)));
}

#endif

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