g711_pcm_convert.c

#include "g711_pcm_convert.h"


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


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

/** 
 * @brief 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(short pcm_val)    /* 2's complement (16-bit range) */  
{  
    short     mask;  
    short     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);  
    }  
}  

/**
 * @brief Convert an A-law value to 16-bit linear PCM 
 * 
 */  
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);  
}

/**
 * @brief 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) */  
{  
    short     mask;  
    short     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);  
    }
}  

/**
 * @brief 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)  
{  
    short     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));  
}

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

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

/**
 * @brief pcm data encode to g711 data
 * 
 *  user should be responsible for pCodecbit memmory
 * 
 * @param pCodecBits store g711 encoded data 
 * @param pBuffer pcm raw data
 * @param BufferSize pcm data len
 * @param type g711 data type
 * @return int encode data length
 */
int G711EnCode(char* pCodecBits, char* pBuffer, int BufferSize, enum g711type type)
{
    unsigned char* codecbits = (unsigned char*)pCodecBits;
    short* buffer = (short*)pBuffer;

    if(pCodecBits == 0 || pBuffer == 0 || BufferSize <= 0)
        return -1;

    if(type == G711ALAW){
        for(int i=0; i<BufferSize/2; i++)  {  
            codecbits[i] = linear2alaw(buffer[i]);  
        }  
    } else {
        for(int i=0; i<BufferSize/2; i++)  {  
            codecbits[i] = linear2ulaw(buffer[i]);  
        } 
    }
    
    return BufferSize/2;  
}   

/**
 * @brief g711 data decode to pcm data
 * 
 * user should be responsible for pRawData memmory
 * 
 * @param pRawData store uncoded pcm data
 * @param pBuffer g711 encoded data
 * @param BufferSize g711 data len
 * @param type g711 data type
 * @return int pcm data len
 */
int G711Decode(char* pRawData, char* pBuffer, int BufferSize, enum g711type type)
{
    short *out_data = (short*)pRawData;  
    unsigned char* buffer = (unsigned char*)pBuffer;

    if(pRawData == 0 || pBuffer == 0 || BufferSize <= 0)
        return -1;

    if(type == G711ALAW) {
        for(int i=0; i<BufferSize; i++){  
            out_data[i] = alaw2linear(buffer[i]);  
        }  
    } else {
        for(int i=0; i<BufferSize; i++){  
            out_data[i] = ulaw2linear(buffer[i]);  
        }
    }

    return BufferSize*2;  
}

/**
 * @brief g711 u-law data and a-law data convert
 * 
 * @param alawdata g711 a-law data
 * @param ulawdata g711 u-lwa data
 * @param datasize input data length
 * @param type target g711 data type
 * @return int sucess:1; failed:0
 */
int G711TypeChange(unsigned char* alawdata, unsigned char* ulawdata, int datasize, enum g711type type)
{
    if(alawdata == 0 || ulawdata == 0 || datasize <= 0)
        return 0;

    if(type == G711ALAW) {
        for(int i = 0; i < datasize; i++) {
            alawdata[i] = ulaw2alaw(ulawdata[i]);
        }
    } else {
        for(int i = 0; i < datasize; i++) {
            ulawdata[i] = alaw2ulaw(alawdata[i]);
        }
    }
    return 1;
}