sacode.cpp

这是G.723和G.729的音频编解码的源代码

#include "stdafx.h"
#include "sactable.h"
#include "color.h"
#include "Cbitstream.h"
#include "sac.h"

SAC::SAC(CBitStream *OutStream)
{	
	low=0;
	high=top;
	opposite_bits=0;
	SAClength=0;
	zerorun=0;
	OutputStream=OutStream;
}

int SAC::AR_Encode(int index, const int *cumul_freq)
{	int bitcount=0;

	if (index<0) return -1; /* Escape Code */

	CodeWord=0;
	CodeLength=0;
	SAClength = high - low + 1;
	high = low - 1 + (SAClength * cumul_freq[index]) / cumul_freq[0];
	low += (SAClength * cumul_freq[index+1]) / cumul_freq[0];

	for ( ; ; )
		{if (high < q2)
			 bitcount+=bit_opp_bits(0);
         else if (low >= q2) 
			{bitcount+=bit_opp_bits(1);	
			 low -= q2; 
			 high -= q2;
			}
		 else if (low >= q1 && high < q3) 
			{opposite_bits += 1; 
			 low -= q1; 
			 high -= q1;
			}
		 else break;
		 low *= 2; 
		 high = 2*high+1;
		}
	if (CodeLength)
		OutputStream->PutVarible(CodeWord>>1,CodeLength);
	return bitcount;
}

int SAC::CodeTCoef(int mod_index, int position, int intra)
{	int length;
	switch (position)
		{case 1:
	        if (intra)
				length = AR_Encode(mod_index, cumf_TCOEF1_intra);
			else
				length = AR_Encode(mod_index, cumf_TCOEF1);
			break;
		 case 2:
            if (intra)
				length = AR_Encode(mod_index, cumf_TCOEF2_intra);
			else
				length = AR_Encode(mod_index, cumf_TCOEF2);
			break;
         case 3:
            if (intra)
				length = AR_Encode(mod_index, cumf_TCOEF3_intra);
			else
				length = AR_Encode(mod_index, cumf_TCOEF3);
			break;
         default:
            if (intra)
				length = AR_Encode(mod_index, cumf_TCOEFr_intra);
			else
				length = AR_Encode(mod_index, cumf_TCOEFr);
			break;
		}
	return length;
}

int SAC::bit_opp_bits(BOOL bit) // Output a bit and the following opposite bits
{	int bitcount=0;

	if (zerorun>13)
		{CodeWord|=1;
		 CodeWord<<=1;
		 bitcount++;
		 CodeLength++;
		 if (CodeLength>=31)
			{OutputStream->PutVarible(CodeWord>>1,CodeLength);
			 CodeWord=0;
			 CodeLength=0;
			}
		 zerorun=0;
		}
	if (bit)
		zerorun=0;
	else
		zerorun++;
	CodeWord|=bit;
	CodeWord<<=1;
	bitcount++;
	CodeLength++;
	if (CodeLength>=31)
		{OutputStream->PutVarible(CodeWord>>1,CodeLength);
		 CodeWord=0;
		 CodeLength=0;
		}
	while(opposite_bits > 0)
		{if (zerorun>13)
			{CodeWord|=1;
			 CodeWord<<=1;
			 bitcount++;
			 CodeLength++;
			 if (CodeLength>=31)
				{OutputStream->PutVarible(CodeWord>>1,CodeLength);
				 CodeWord=0;
				 CodeLength=0;
				}
			 zerorun=0;
			}
		 if (!bit)
			 zerorun=0;
		 else
			 zerorun++;
		 CodeWord|=!bit;
		 CodeWord<<=1;
		 bitcount++;
		 CodeLength++;
		 if (CodeLength>=31)
			{OutputStream->PutVarible(CodeWord>>1,CodeLength);
			 CodeWord=0;
			 CodeLength=0;
			}
		 opposite_bits--;
		}
	return bitcount;
}

int SAC::encode_flush()
{	int bitcount = 0;

	CodeWord=0;
	CodeLength=0;
	opposite_bits++;
	if (low < q1)
		bitcount+=bit_opp_bits(0);
    else 
		bitcount+=bit_opp_bits(1);

	low = 0; 
	high = top;
	zerorun=0;
	if (CodeLength)
		OutputStream->PutVarible(CodeWord>>1,CodeLength);
	return bitcount;
}

int SAC::IndexFN(int value, const int *table, int max)
{	int n=0;

	while(1)
		{if (table[n++]==value) 
			return n-1;
		 if (n>max) 
			return -1;
		}
}