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DSP(3)			   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 sig-
       nal 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 ar-
       ray 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  coeffi-
       cients 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	 inte-
       gers, 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)

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