NAME

       initdp,   freedp,  dotprod,  sumsq,  peakval  - SIMD-assisted  digital  signal  processing
       primitives

SYNOPSIS

       #include "fec.h"

       void *initdp(signed short *coeffs,int len);
       long dotprod(void *p,signed short *a);
       void freedp(void *p);

       unsigned long long sumsq(signed short *in,int cnt);

       int peakval(signed short *b,int cnt);

DESCRIPTION

       These functions provide several basic  primitives  useful  in  digital  signal  processing
       (DSP),  especially  in  modems.   The  initdp,  dotprod  and freedp functions implement an
       integer dot product useful in  correlation  and  filtering  operations  on  signed  16-bit
       integers.  sumsq  computes  the  sum of the squares of an array of signed 16-bit integers,
       useful for measuring the energy of a signal. peakval returns the  absolute  value  of  the
       largest magitude element in the input array, useful for scaling a signal's amplitude.

       Each  function  uses  IA32  or  PowerPC  Altivec instructions when available; otherwise, a
       portable C version is used.

USAGE

       To create a FIR filter or correlator, call initdp with the coefficients in coeff and their
       number in len.  This creates the appropriate data structures and returns a handle.

       To  compute  a dot product, pass the handle from initdp and the input array to dotprod. No
       length field is needed as the number of samples will  be  taken  from  the  len  parameter
       originally  given  to initdp. There must be at least as many samples in the input array as
       there were coefficients passed to initdp.

       When the filter or correlator is no longer needed, the data structures  may  be  freed  by
       passing the handle to freedp.

       The user is responsible for scaling the inputs to initdp and dotprod, as the 32-bit result
       from dotprod will silently wrap around in the event of overflow.

       To compute the sum of the squares of an array of signed 16-bit integers, use  sumsq.  This
       returns a 64 bit sum.

       peakval  computes the absolute value of each 16-bit element in the input array and returns
       the largest.

RETURN VALUES

       initdp returns a handle that points to a control block, or NULL in the event of  an  error
       (such as a memory allocation failure). sumsq and peakval have no error returns.

AUTHOR and COPYRIGHT

       Phil Karn, KA9Q (karn@ka9q.net)

                                                                                           DSP(3)