/*---------------------------------------------------------------------------
polyeval.asm:   N-Order Polynomial Evaluation of two values
-----------------------------------------------------------------------------
Description:

Evaluates the N-order polynomial
                 N
                ___         i
        f(x) =  \     c  * x             ( contains N+1 terms )
                /__    i
                i=0

which can be factored as


        f(x) = ( ( ... ( ( c   * x  + c    ) * x + c    ) * x ... + c
                            N          N-1          N-2              0

To evaluate a single value requires two instructions in the inner loop, since
the multiply-add operations cannot be pipelined for this algorithm.  Because
of the ADSP-21020's multifunction instructions, two values can be evaluated
simultaneously in the inner loop in just two instructions.

-----------------------------------------------------------------------------
Program Characteristics:

Calling Values:

    REGISTER FILE:
    f0 = input datum #1
    f1 = input datum #2
    r2 = N-2 = polynomial order minus two

    DAG1 (Data Memory):
    i0 = index to coefficients ( ordered c   --> c  )
    l0 = N+1                              N       0
    m0 = +0
    m1 = +1

Computation Time = 2N+9 cycles FOR TWO EVALUATIONS
                 = N+4.5 cycles per evaluation
                 = 380ns per 5th order evaluation @ 25MHz
                 = 2.6 million 5th order evaluations/sec @ 25MHz

-----------------------------------------------------------------------------
Note:
    For order < 3, use straight-line code (no loops)

-----------------------------------------------------------------------------
Author:     Jim Donahue, Analog Devices DSP Division
Revised:    14-AUG-91
----------------------------------------------------------------------------*/
.GLOBAL polyeval;

#define N_M2    r2
#define CN      f12

#define X1      f0
#define SUM1    f4
#define PROD1   f8

#define X2      f1
#define SUM2    f5
#define PROD2   f9

.SEGMENT /pm    pm_code;
polyeval:
        SUM1  = dm(i0,m0);
        SUM2 = SUM1;
        PROD1 = X1 * SUM1, CN = dm(i0,m0);
        PROD2 = X2 * SUM2, SUM1  = PROD1 + CN;

        lcntr = N_M2, do plp until lce;
            PROD1 = X1 * SUM1, SUM2  = PROD2 + CN, CN = dm(i0,m0);
plp:        PROD2 = X2 * SUM2, SUM1  = PROD1 + CN;

        PROD1 = X1 * SUM1, SUM2  = PROD2 + CN, CN = dm(i0,m0);
        rts(db);
            PROD2 = X2 * SUM2, f0  = PROD1 + CN;
            f1  = PROD2 + CN;

.ENDSEG;