ITU-g711程序源码

// ITU-g711程序源码
// 主要包括：
// 13比特线性码的U律编码解码。
// 13比特线性码的U律编码解码。
// U律和A律8位非线性吗之间的相互转换。

#define SIGN_BIT    (0x80)      /* A-law 符号位  */
#define QUANT_MASK  (0xf)       /* 段内量化值域  */
#define NSEGS       (8)         /* A-law 段落号. */
#define SEG_SHIFT   (4)         /* 段落左移位量  */
#define SEG_MASK    (0x70)      /* 段落码区域.   */

static short seg_aend[8] = {0x1F, 0x3F, 0x7F, 0xFF, 0x1FF, 0x3FF, 0x7FF, 0xFFF};  //A律编码解码预制表
static short seg_uend[8] = {0x3F, 0x7F, 0xFF, 0x1FF,0x3FF, 0x7FF, 0xFFF, 0x1FFF}; //U律编码解码预制表

unsigned char _u2a[128] = {         /* U律到A律转化编码表 */
    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,
    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律到U律转化编码表 */
    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, 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};
// 该子程序寻找段落码
static short search(    short       val,    short       *table, short       size)
{
    short       i;
    for (i = 0; i < size; i++)
    {
        if (val <= *table++)
        return (i);
    }
    return (size);
}

/*  输入与输出码型对应表
 *  线性码输入              非线性码输出
 *  ----------------      --------------
 *  0000000wxyza            000wxyz
 *  0000001wxyza            001wxyz
 *  000001wxyzab            010wxyz
 *  00001wxyzabc            011wxyz
 *  0001wxyzabcd            100wxyz
 *  001wxyzabcde            101wxyz
 *  01wxyzabcdef            110wxyz
 *  1wxyzabcdefg            111wxyz
 */
//16bit 线性码编码为8比特A律非线性码
//输入 pcm_val--16比特线性码，输出8比特A律非线性码
unsigned char linear2alaw(short pcm_val)    /* 2's complement (16-bit range) */
{
    short       mask;
    short       seg;
    unsigned char   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;
    }
    seg = search(pcm_val, seg_aend, 8);  /* 按照输入绝对值求取段落号. */
    // 将求取的符号位, 段落号, 段内量化值组成一个8比特数输出/
    if (seg >= 8)  return (unsigned char) (0x7F ^ mask);
    else {
        aval = (unsigned char) seg << SEG_SHIFT;
        if (seg < 2)aval |= (pcm_val >> 1) & QUANT_MASK;
        else
            aval |= (pcm_val >> seg) & QUANT_MASK;
        return (aval ^ mask);
    }
}

//8bitA律非线性码解码为16比特线性码编码
//输入8比特A律非线性码 ，输出pcm_val--16比特线性码
short alaw2linear(  unsigned char   a_val)
{
    short       t;
    short       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)      //   线性码偏移值
#define CLIP         8159       //   最大量化级数量

/*
//16bit 线性码编码为8比特u律非线性码
//输入 pcm_val--16比特线性码，输出8比特u律非线性码
 *  线性码输入              非线性码输出
 *  ----------------      --------------
 *  00000001wxyza           000wxyz
 *  0000001wxyzab           001wxyz
 *  000001wxyzabc           010wxyz
 *  00001wxyzabcd           011wxyz
 *  0001wxyzabcde           100wxyz
 *  001wxyzabcdef           101wxyz
 *  01wxyzabcdefg           110wxyz
 *  1wxyzabcdefgh           111wxyz
 */
unsigned char linear2ulaw(  short pcm_val)  /* 16比特线性码 */
{
    short       mask;
    short       seg;
    unsigned char   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;        /* 削波 */
    pcm_val += (BIAS >> 2);

    /* Convert the scaled magnitude to segment number. */
    seg = search(pcm_val, seg_uend, 8);
    // 将求取的符号位, 段落号, 段内量化值组成一个8比特数输出/
    if (seg >= 8)
        return (unsigned char) (0x7F ^ mask);
    else {  uval = (unsigned char) (seg << 4) | ((pcm_val >> (seg + 1)) & 0xF);
        return (uval ^ mask);
    }

}
//8bit u律非线性码解码为16bits 线性码编码
//输入u_val 8比特u律非线性码 ，输出pcm_val--16比特线性码
short ulaw2linear(  unsigned char   u_val)
{
    short       t;
    u_val = ~u_val;
    t = ((u_val & QUANT_MASK) << 3) + BIAS;
    t <<= ((unsigned)u_val & SEG_MASK) >> SEG_SHIFT;

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

/*按照A律到U律转化编码表进行A律到U律码型转换 */
unsigned char alaw2ulaw(    unsigned char   aval)
{
    aval &= 0xff;
    return (unsigned char) ((aval & 0x80) ? (0xFF ^ _a2u[aval ^ 0xD5]) :
        (0x7F ^ _a2u[aval ^ 0x55]));
}
/*按照U律到A律转化编码表进行U律到A律码型转换 */
unsigned char ulaw2alaw(    unsigned char   uval)
{
    uval &= 0xff;
    return (unsigned char) ((uval & 0x80) ? (0xD5 ^ (_u2a[0xFF ^ uval] - 1)) :
        (unsigned char) (0x55 ^ (_u2a[0x7F ^ uval] - 1)));
}