arith_decoder_mpeg4.asm

ADI公司出品的blackfin533芯片

    
__arith_decoder_mpeg4:

    P0 = R1;                // Address of structure decoder
    [--SP] = (R7:5);        // Push R7:5
    R2 = R0-R0(NS)||R6 = [P0];
                            // fetch value of lower range register 
    BITSET(R2,16);          // set r2 = 0x8000
    R2 = R2-R0(NS)||R7 = [P0+4];
                            // R0 = probability of '0'.R2 = probability of'1' 
                            // and get Range value 
    R5 = R7>>16;            // Higher 16 bits of range register
    CC = R2<R0;             // check if  probability of '0' is greater then 
                            // probability of '1'
    IF CC R0 = R2;          // probability of LPS (CLPS)
    R3 = CC;                // R3 == Least probable symbol
    R5 = R5.L*R0.L(FU);     // Range LPS(rLPS) ==  R * CLPS
    R7 = R7-R5(NS);         // Range == Range -range of LPS
    R2 = R6+R7(NS);         // Lower value  +=  Range -range of LPS
    R0 = R3<<0||R1 = [P0+8];// fetch decoder->V register
    R1 = R1-R6(NS);         // decoder->V - decoder->L
    BITTGL(R0,0);           // opposite of LPS
    CC = R7 <= R1(IU);      // check if (decoder->R-rLPS) < = 
                            // (decoder->V-decoder->L)
    IF CC R7 = R5;          // if true Range ==  range of LPS
    IF !CC R3 = R0;
    IF !CC R2 = R6;         // if false lower range  ==  previous lower range
    [P0+4] = R7;            // store Range value in decoder->R register
    R7 = R3<<0||[P0] = R2;  // store decoder->L register
    [--SP] = RETS;          // Push RETS register before calling a function
    R0 = P0;                // argument to function decode_renormlise
    CALL __decode_renormlise;
    RETS = [SP++];          // Pop RETS register
    R0 = R7;
    (R7:5) = [SP++];        // Pop R7:5
    RTS;  
    NOP;

__arith_decoder_mpeg4.end:    
/*******************************************************************************
Prototype  : void decode_renormlise(Arcoder *decoder);

As long as decoder->R is smaller than QUATER(0x40000000), renormalization is 
performed.
If the interval(L,L+R) is within [0,HALF], the interval is scaled to [2L,2(L+R)]
and V is scald to 2V. If the interval(L,L+R) is within [HALF,1], the interval is
scaled to [2(L-HALF),2(L-HALF+R)] and V is scald to 2(V-HALF). Otherwise the 
interval is scaled to 2(L-QUATER),2(L-QUATER+R) and V is scaled to 2(V-QUATER).
After each scaling, a bit is read and copied into the least significant bit of 
register decoder->V.

Registers used : R0-R3, R6, R7, P0-P2, P5.
*******************************************************************************/
.section                       program;
.global            __decode_renormlise;
.align                               8;
__decode_renormlise:

    P0 = R0;                // Address of structure decoder 
    [--SP] = (R7:6);        // Push R7:6,P5
    [--SP] = P5;
    [--SP] = RETS;
    P5 = R0;                // Duplicate the address of coder
    R7 = R1-R1(NS)||R0 = [P0];
                            // fetch coder->L 
    R6 = R0-R0(NS)||R1 = [P0+4];
                            // fetch coder->R 
    BITSET(R7,31);          // set r7 == 0x80000000
    BITSET(R6,30);          // set r6 == 0x40000000
CHK_WHILE:
    CC = R1<R6(IU);
                            // check if code->R <0x40000000 
    IF !CC JUMP NORME_END;  // if false jump to NORME_END
    CC = R7 <= R0(IU);      // check if coder->L >0x80000000
    IF !CC JUMP CHK_ELSE_IF;
    R0 = R0-R7(NS)||R1 = [P0+8];
                            // coder->L -= 0x80000000 
    R1 = R1-R7(NS)||[P0] = R0;
                            // store coder->L value 
    [P0+8] = R1;            // decoder->V -= HALF
    JUMP END_WHILE;
CHK_ELSE_IF:
    R2 = R0+R1;   // Add decoder->L and decoder->R
    CC = R2 <= R7(IU);      // check if coder->L+coder->R < = 0x80000000
    IF CC JUMP END_WHILE;
    R0 = R0-R6(NS)||R1 = [P0+8];
                            // decrement coder->L by 0x40000000 
    R1 = R1-R6(NS)||[P0] = R0;
                            // store modified coder->L value 
    [P0+8] = R1;            // decoder->V -= QUATER
END_WHILE:
    R0 = [P0];
    R0 = R0<<1||R1 = [P0+4];// double coder->L
    R1 = R1<<1||[P0] = R0;  // double coder->R
    [P0+4] = R1;            // and store updated values
    R0 = P5;

    CALL __AddNextInputBit; // get next bit and copy to LSB of 
                            // decoder->V register
    R0 = [P5];
    R1 = [P5+4];            // fetch updated value of decoder->L ,R registers
    JUMP CHK_WHILE;         // repeat the procedure till coder->R < 0x40000000
    
NORME_END:
    RETS = [SP++];
    P5 = [SP++];
    (R7:6) = [SP++];        // POP RETS and R7:6,P5 register
    RTS;
    NOP;
__decode_renormlise.end:    
/******************************************************************************
Prototype : void  AddNextInputBit(ArDecoder *decoder);
In this procedure any stuffed bits are removed. One bit is read from input array
and copied to LSB of V register.

Registers used : R0-R3, P0-P2.
*******************************************************************************/
.section                 program;
.global               __AddNextInputBit;
.align                        8;
    
__AddNextInputBit:

    P0 = R0;                // address of structure decoder
    R1 = 1; 
    R3 = [P0+12];           // fetch decoder->arpipe
    R2 = R3>>30||P1 = [P0+52];
                            // fetch address of input array 
    CC = BITTST(R2,0);      // check input bit  == 1
    IF CC JUMP ELSE_CONDITION;
    R2 = [P0+24];
    R2 += -1;
    [P0+24] = R2;           // decrement decoder->nzeors by 1
    CC = R2 == 0;
    IF !CC JUMP COND_OVER;
    R0 = [P0+36];           // fetch decoder->extrabits
    R0 = R0-R1(NS)||R2 = B[P1++](Z);
                            // flush a stuffed bit 
    [P0+36] = R0;           // store decoder->extrabits  += -1
ELSE_CONDITION:
    R2 = [P0+44];           // fetch decoder->mm
    [P0+28] = R1;           // store decoder->nonzero
    [P0+24] = R2;           // store decoder->nzerof  = decoder->mm
COND_OVER:
    R0 = 31; 
    R3 = R3<<1||R1 = [P0+36];  
    R0 = R0+R1(NS)||R2 = B[P1++](Z);
                            // flush a bit 
    P2 = R0;                // offset to fetch current bit
    R2 = [P0+8];            // fetch decoder->V
    R2 = R2<<1;             // shift left decoder->nzerof by 1 and fetch nzerof
    R0 = 1;
    P2 = P2+P1;
    R1 = B[P2](Z);          // fetch a bit
    R1 = R1&R0;
    R2 = R2+R1(NS)||R0 = [P0+32];
                            // add bit to LSB of decoder->V 
    R3 = R3+R1(NS)||[P0+8] = R2;
                            // add bit to LSB of decoder->arpipe 
    CC = R1 == 0;             
    IF !CC JUMP NO_DECREMENT;
    R0 += -1;
    [P0+32] = R0;           // decrement decoder->nzerof
    CC = R0 == 0;
    IF !CC JUMP OVER;
    R0 = [P0+36];
    R0 += 1;
    [P0+36] = R0;
NO_DECREMENT:
    R0 = [P0+44];           // fetch decoder->mm
    [P0+32] = R0;           // store decoder-> nzerof as decoder->mm
OVER:
    [P0+12] = R3;           // store decoder-> arpipe
    [P0+52] = P1;           // store the current pointer of input array
    RTS;
    NOP;
__AddNextInputBit.end:    
/*******************************************************************************
Prototype : void StopArDecoder( ArDecoder *decoder);

After the last symbol has been decoded,additional bits need to be consumed which
are introduced by the encoder for proper decodability. In general 3 further bits
need to be read. However in some cases, only 2 bits need to be read. These cases
are defined by
i)  if the current interval covers entirely[QUATER-1,HALF]
ii) if the current interval covers entirely [ HALF-1, 3*QUATER].

Registers used : R0-R3, R5-R7, P0-P2, P5.
*******************************************************************************/
.section             program;
.global             __StopArDecoder;
.align                      8;
    
__StopArDecoder:
    P0 = R0;                // Address of decoder
    [--SP] = (R7:5,P5:5);   // Push R7:5,P5 and RETS register
    P5 = R0;                // store the address in P5
    R0 = [P0];              // get value of coder->L
    R3 = 8;    
    R7 = R0>>29||R2 = [P0+4];
                            // fetch value of coder->R 
    R6 = R0+R2;            
    R6 = R6>>29;             
    CC = R6 == 0;
    IF CC R6 = R3;
    R6 = R6-R7;
    CC = R6 == 3;
    R2 = CC;
    CC = BITTST(R7,0);      // conditional check to find how many bits to read
    R1 = CC;
    [--SP] = RETS;       
    R0 = P5;
    R7 = R2&R1;
    
    CALL __AddNextInputBit; // fetch next bits and copy to LSB of 
                            // decoder->V reg.
    CC = R6 <= 3;
    IF !CC JUMP CALL_END;
    CC = R7 == 1;
    IF CC JUMP CALL_END;
    R0 = P5;
    CALL __AddNextInputBit; // fetch next bits and copy to LSB of 
                            // decoder->V reg.
    
CALL_END:
    R0 = [P5+28];            
    CC = R0 == 0;           // check if nzeros == 0
    IF CC JUMP FLUSH_BITPLUS;
                            // if true flush a bit 
    R1 = [P5+44];
    R2 = [P5+48];           // get difference of decoder->mm-decoder->mt
    R1 = R1-R2(NS)||R0 = [P5+24];
    CC = R0<R1;
    IF !CC JUMP NO_CALL;
FLUSH_BITPLUS:
    P1 = [P5+52];          
    R0 = B[P1++](Z);
    [P5+52] = P1;           // flush the final bit
NO_CALL:
    RETS = [SP++];
    (R7:5,P5:5) = [SP++];
    RTS;
    NOP;                    //to avoid one stall if LINK or UNLINK happens to be
                            //the next instruction after RTS in the memory.    
__StopArDecoder.end: