/*******************************************************************************
Copyright(c) 2000 - 2002 Analog Devices. All Rights Reserved.
Developed by Joint Development Software Application Team, IPDC, Bangalore, India
for Blackfin DSPs  ( Micro Signal Architecture 1.0 specification).

By using this module you agree to the terms of the Analog Devices License
Agreement for DSP Software. 
********************************************************************************
Module Name     : arith_decoder_JPEG2000.asm
Label Name      : __arith_decoder_JPEG2000
Version         :   2.0
Change History  :

                Version     Date          Author        Comments
                2.0	    01/09/2007    Arjun	        Tested with VDSP++4.5
							Compiler 7.2.3.2
		1.3         11/18/2002    Swarnalatha   Tested with VDSP++ 3.0
                                                        compiler 6.2.2 on 
                                                        ADSP-21535 Rev.0.2
                1.2         11/13/2002    Swarnalatha   Tested with VDSP++ 3.0
                                                        on ADSP-21535 Rev. 0.2
                1.1         03/20/2002    Raghavendra   Modified to match
                                                        silicon cycle count
                1.0         08/29/2001    Raghavendra   Original 

Description     : The compressed data CD and contexts are supplied to decoder 
                  and output will be a decision bit D either 0 or 1. The encoder
                  and decoder must use same set of contexts to get proper 
                  result.
                  Docoder decodes one binary decision at a time. After decoding 
                  the decision, decoder subtracts any amount from the compressed
                  data that the encoder added.

                  The  following structures are  used for arithmetic decoding. 
                  1.
                       struct  mqdec
                         {
                           int A;      -> interval register (range:0,75 <=A<1,5)
                           int C;      -> code register
                           int CT;     -> bit counter register
                           int B;      -> byte value
                           unsigned char *input;   -> array where compressed 
                                                      data to be read
                           unsigned char *out;     -> array where output is 
                                                      stored
                          }dec_reg;

                  2. struct contexts
                    {
                       int index;       -> index to probability estimation table
                       int mps;         -> MPS value for particular context.
                    } contexts[18];     -> array of contexts( 18 for JPEG 2000)

                  3. struct mqstates
                     {
                       int Qe;          -> value of probability of LPS
                       int NMPS;        -> Next index when MPS is coded
                       int NLPS;        -> Next index when LPS is coded
                       int SWITCH;      -> To change mps value when LPS is coded
                     }mqstates_s[47];

Assumptions     : 1. mqstate_s[47] table and   struct  mq_enc variable are in 
                     different banks.

                  2. mqstates_s[47] is initialized with probability values as 
                     specified in Table C-2 of Annex-C,ISO/IEC FCD15444-1:2000
                     (V1.0,16 March 2000)

                  3. Index and MPS values for each context is initialized before
                     starting encoder.

                  Note : Two 0xFF appended at the end of input bitstream for 
                  testing purpose(refer Annex D, section D.4.1 of ISO/IEC 
                  FCD15444-1:2000(V1.0,16 March 2000).

Prototypes      : void arith_decode_init(struct mqdec *, unsigned char *input , 
                                        unsigned char *output);

                  void  arith_decoder_JPEG2000(unsigned char CX,struct mqdec *, 
                                     struct mqstates *,struct contexts*);

                  void  arith_decode_renorme(struct mqdec*);

                  void  arith_decode_bytein(struct mqdec*);

Calling sequence : Arith_decode_init function is called for initialization. 
                   arith_decoder_JPEG2000 function is called for each context.
                   C implementation of calling sequence is explained below.

                   main() or func()
                   { 
                      int i;
                      struct enc_reg mq_enc;
                        .
                        .
                        .
                       arith_decode_init(&mq_enc,&arrayOut[0]);
                      for(i=0;i<NUMBER_OF_CONTEXT;i++)
                      {
                        CX=context_input[i];
                        arith_decoder_JPEG2000(CX, *mq_enc, mqstates,contexts);
                      }
                       
                      .
                      .
                   }

Performance     :
 
                Code Size :
                    arith_decode_init       : 68  bytes
                    arith_decode_bytein     : 104 bytes
                    arith_decode_renorme    : 64  bytes
                    arith_decoder_JPEG2000  : 228 bytes
                                       
                                                      Best case    Worst case
                  Cycle count : arith_decode_init      : 46           46  cycles
                                arith_decoder_JPEG2000 : 42           201 cycles

                  Cycle count mentioned is for a particular input sequence.
                  As the algorithm is data dependant, Cycle count may vary.

                  For e.g ,Cycle count for 5760 output symbols which take 
                  23 bytes as input is 288161 (i.e 46.61 cycles per output 
                  symbol).

Reference       : Annex - C Arithmetic entropy encoding (JPEG-2000)
                  ISO/IEC FCD15444-1:2000(V1.0,16 March 2000)

Registers used  : R0-R3, R6, R7, I0, M0, L0, P0-P2, P5.
*******************************************************************************/
.section    L1_code;
.global     __arith_decoder_JPEG2000;
.align      8;
    
__arith_decoder_JPEG2000:         
    R0 = R0 << 3; 
     P2 = [SP+12];
    P0 = R0;                // Offset to fetch current context
                           // Address of contexts 
    L0 = 0;
    I0 = R2;                // address of mqstates values
    [--SP] = P5;
    P5 = R1;                // address of structure mqdec
    P0 = P2+P0;             // Point to current context
    R2 = [P0++];            // get index value from current context
    R2 = R2 << 4;
    R3 = [P0--];
                            // get MPS value of current context 
    M0 = R2;
    [--SP] = (R7:6);        // Push R7:6
    P2 = R1;             
    [--SP] = RETS;          // Push RETS reg
    R2 = [P5];
    R0 = [I0++M0];
                            // fetch A register, dummy fetch to increment the 
                            // pointer 
    R1 = R2-R2(NS);
    R7 = [I0++];
                            // clear R1 and fetch Qe value 
    R2 = R2-R7(NS);
    R6 = [P5+4];
                            // do A-Qe and fetch C register 
    R1 = PACK(R1.H,R6.H);
    NOP;   // get C high register value
    CC = R1<R7;             // compare Chigh < Qe
    IF CC JUMP LPS_EXCHANGE;// if true code as LPS-EXCHANGE
    R1 = R1-R7(NS);         // Chigh = Chigh - Qe
    R1 = PACK(R1.L,R6.L);
    [P5] = R2;
                            // store A register value 
    [P5+4] = R1;            // store C register
    P1 = [P5+20];
    R0 = [I0++];
                            // address of output array 
    CC = BITTST(R2,15);     // check if a> 0x8000
    IF CC JUMP D_EQ_MPS;    // if true jump to D_EQ_MPS

/************** MPS_EXCHANGE ********************/
    CC = R2<R7;             // compare A< QE
    IF CC JUMP CHECK_SWITCH;// if true jump to CHECK_SWITCH
    B[P1++] = R3;           // store output D =  = mps(CX)
    [P5+20] = P1;           // get value NMPS index
    [P0++] = R0;            // store next index as NMPS value for present 
                            // context
    JUMP CALL_RENORME;
    
CHECK_SWITCH:
    R2 = R3 << 0;
    R0 = [I0++];
                            // dummy fetch to increment I0 
    BITTGL(R2,0);           // complement MPS value
    R1 = [I0++];
    [P0++] = R0;
                            // store NLPS and fetch SWITCH value 
    CC = R1 == 1;         // check if SWITCH flag is set
    R0 = CC;
    B[P1++] = R2;
    [P5+20] = P1;
    R3 = R0^R3;             // XOR the result to compliment MPS value if SWITCH
                            // flag is set
    [P0] = R3;              // store MPS value
    JUMP CALL_RENORME;
    
D_EQ_MPS:
    RETS = [SP++];          // pop RETS register 
    B[P1++] = R3;           // store output bit  = mps(CX)
    [P5+20] = P1;           // store address where next output to be stored
    (R7:6) = [SP++];
    P5 = [SP++];            // pop R7:6,P5
    RTS;
    NOP;                    // To remove stalls occurring on the board

/********************** LPS_EXCHANGE    ****************************/