lattice-ladder filters for SHARC

Started by keith July 16, 2003
Anyone know where to find assembly routines for SHARC to perform lattice-ladder
filters?
E.g. analysis (decimate) section:

  input ------------ 2:1 ------ + --------------- + ------- .... ---> output1
          |                   X                 X
          T               *a0  *-a0         *a1  *-a1
          |               /       \         /       \
           -- *-1 -- 2:1 ---------- + -- T ---------- + --- .... ---> output2

                                       |    stage 1     |
                                        ----------------

    pstate=&state[0];
    pcoeff=&coeff[0];

    *Output1 = -(*Input)*(*pcoeff);
    *Output2 = -(*Input++);
    (*Output1) += *Input;
    (*Output2) -= (*Input++)*(*pcoeff++);

    LOOP(NumberOfCoefficients-1)
      temp = *Output2;
      *Output2 = (*pstate) - ((*Output1)*(*pcoeff));
      *Output1 += ((*pstate)*(*pcoeff++));
      *pstate++ = temp;
    ENDLOOP

    Output1++;
    Output2++;

synthesis section:

  input1 -------- + - T -- .... -------- + ------ 1:2 ----------
                X                      X                       |
            *-aj *aj              *-a0 *a0                 T
            /       \              /       \                   |
  input2 ------------ + -- .... ------------ + -- 1:2 -- *-1 -- + ---> output

         |    stage j    |
          ---------------

    pstate=&state[0];
    pcoeff=&coeff[NumberOfCoefficients-1];

    sum1 = (*Input1) - ((*Input2)*(*pcoeff));
    sum2 = (*Input2++) + ((*Input1++)*(*pcoeff--));

    LOOP(NumberOfCoefficients-1)
      temp = sum1;
      sum1 = (*pstate) - (sum2*(*pcoeff));
      sum2 += ((*pstate)*(*pcoeff--));
      *pstate++ = temp;
    ENDLOOP

    (*Output++) = -sum2;
    (*Output++) = sum1;

Thx.

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keith <keith> wrote:

> Anyone know where to find assembly routines for SHARC to perform > lattice-ladder filters? E.g. analysis (decimate) section: >
Hello Keith, I tried a modified SOS structure, at first in C (hand optimized), then in assembler (as good as I could), then after a discussion with compiler people from VDSP, I rewrote the C code so that it didn't contain any of my usual optimizations any more, and I compared the results: worst performance had the C code which I optimized before compilation. The non-optimized code passed the internal optimization stage of the compiler, and then performed pretty much the same as the assembly code. The overall behaviour of the C coded solution was even better in some situation. It should be easy to write C code out of what you posted here. Programme it straightforward, compile it with compiler optimization activated and check if it meets your requirements. If not, it should be very hard to solve this by translating it into the assembly language. just my 2c. Bernhard -- before sending to the above email-address: replace deadspam.com by foerstergroup.de