Momentum-Apps/g711.c

/*
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 * 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
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 *
 * Sun source code is provided with no support and without any obligation on
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 * 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.
 */
#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)));
}