g711.java

结构非常清晰的SIP协议栈

package local.media;



/** G.711 codec.
  * This class provides methods for u-law, A-law and linear PCM conversions.
  */
public class G711
{
   static final int SIGN_BIT=0x80;    // Sign bit for a A-law byte.
   static final int QUANT_MASK=0xf;   // Quantization field mask.
   static final int NSEGS=8;          // Number of A-law segments.
   static final int SEG_SHIFT=4;      // Left shift for segment number.
   static final int SEG_MASK=0x70;    // Segment field mask.
  
   static final int[] seg_end={  0xFF, 0x1FF, 0x3FF, 0x7FF, 0xFFF, 0x1FFF, 0x3FFF, 0x7FFF  };
  
   // copy from CCITT G.711 specifications
   
   /** u- to A-law conversions */
   static final int[] _u2a={
     	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  };
     	
   /** A- to u-law conversions */
   static final int[] _a2u={
     	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,	int[] table)
   {  for (int i=0; i<table.length; i++) if (val<=table[i]) return i;
      return table.length;
   }

  
   /** Converts a 16-bit linear PCM value to 8-bit A-law.
     *
     * It 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.
     */
   public static int linear2alaw(int pcm_val) // 2's complement (16-bit range)
   {  int mask;
  	   int seg;
  	   //unsigned char aval;
      int 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);
     
     	// 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);
     	}
   }
  
   /** Converts an A-law value to 16-bit linear PCM
     */
   //public static int alaw2linear(unsigned char a_val)
   public static int alaw2linear(int a_val)
   {  int t;
      int seg;
  	   a_val^=0x55;   
     	t=(a_val&QUANT_MASK)<<4;
     	//seg=((unsigned)a_val&SEG_MASK)>>SEG_SHIFT;
      seg=(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)!=0)? t : -t;
   }
  
  
   /** Bias for linear code. */
   public static final int BIAS=0x84;


   /** Converts 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.
     */
   public static int linear2ulaw(int pcm_val)	// 2's complement (16-bit range)
   {  int mask;
      int seg;
      //unsigned char uval;
      int 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);
  
  	   // Combine the sign, segment, quantization bits; and complement the code word.

     	if (seg>=8) return (0x7F^mask); // out of range, return maximum value.
     	else
     	{  uval=(seg<<4) | ((pcm_val>>(seg+3)) & 0xF);
         return (uval^mask);
  	   }
   }
  
   /** ConvertS 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.
     */
   //public static int ulaw2linear(unsigned char u_val)
   public static 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<<=((unsigned)u_val&SEG_MASK)>>SEG_SHIFT;
      t<<=(u_val&SEG_MASK)>>SEG_SHIFT;
     
     	return ((u_val&SIGN_BIT)!=0)? (BIAS-t) : (t-BIAS);
  }

  
   /** A-law to u-law conversion.
     */
   //public static int alaw2ulaw(unsigned char aval)
   public static int alaw2ulaw(int aval)
   {  aval&=0xff;
  	   return ((aval & 0x80)!=0)? (0xFF^_a2u[aval^0xD5]) : (0x7F^_a2u[aval^0x55]);
   }

  
   /** u-law to A-law conversion.
     */
   //public static int ulaw2alaw(unsigned char uval)
   public static int ulaw2alaw(int uval)
   {  uval&=0xff;
  	   return ((uval&0x80)!=0)? (0xD5^(_u2a[0xFF^uval]-1)) : (0x55^(_u2a[0x7F^uval]-1));
   }

   
   /** PCM ecoder/decoder tests. */
   /*public static void main(String[] args)
   {
      for (int i=0; i<0xFF; i++)
      {  int pcmu,pcma,linear;
         pcmu=i;
         System.out.print("  pcmu:"+pcmu);
         pcma=ulaw2alaw(pcmu);
         System.out.print("  pcma:"+pcma);
         pcmu=alaw2ulaw(pcma);
         System.out.print("  pcmu:"+pcmu);
         linear=alaw2linear(pcma);
         System.out.print("  linear:"+linear);
         pcma=linear2alaw(linear);
         System.out.print("  pcma:"+pcma);
         linear=ulaw2linear(pcmu);
         System.out.print("  linear:"+linear);
         pcmu=linear2ulaw(linear);
         System.out.print("  pcmu:"+pcmu);
         System.out.println(" .");
         if (i%20==19)
         try {  System.in.read();  } catch (Exception e) {}
      }
   }*/
}