DragonFly On-Line Manual Pages

DSP(3)                DragonFly Library Functions Manual                DSP(3)

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)