sco
is capable of handling different coding techniques that often used to implement
many of DSP algorithms.
For example the classical DSP kernel for "NTAPS"-tap FIR filter
processing "NPOINTS" points
void fir( int *input, /* pointer to input
sample array of NTAPS points*/
int *output, /* pointer to output array of NPOINTS
points */
int *coefficient /* pointer to coefficient array of NTAPS values */
)
{
int i, j;
int *data, *coef, *initial;
int sum;
int tmp1, tmp2;
initial = input;
for ( i = 0; i < NPOINTS; i++
)
{
data = input++;
coef = coefficient;
sum = 0;
for (j = 0; j <
NTAPS; j++)
{
tmp1 =
*data;
if ( data
== initial )
{
data = initial + ( NTAPS - 1 );
}
else
{
data--;
}
tmp2 =
*coef++;
sum +=
tmp1 * tmp2;
}
*output++ = sum;
}
}
may be coded with:
1. use of "pointers":
void fir( int *input, /* pointer to input sample
array of NTAPS points*/
int *output, /* pointer to output array of NPOINTS
points */
int *coefficient /* pointer to coefficient array of NTAPS values */
)
{
int i, j;
int *data, *coef, *initial;
int sum;
int tmp1, tmp2;
initial = input;
for ( i = 0; i < NPOINTS;
i++ )
{
data = input++;
coef = coefficient;
sum = 0;
for (j = 0; j <
NTAPS; j++)
{
tmp1
= *data;
if (
data == initial )
{
data = initial + ( NTAPS - 1 );
}
else
{
data--;
}
tmp2
= *coef++;
sum
+= tmp1 * tmp2;
}
*output++ = sum;
}
}
2. use of "pointers with a swap":
void fir( int *input, /* pointer
to input sample array of NTAPS points*/
int *output, /* pointer to output array of
NPOINTS points */
int *coefficient /* pointer to coefficient array of NTAPS values */
)
{
int i, j;
int *data, *coef, *initial;
int sum;
int tmp1, tmp2;
initial = input;
for ( i = 0; i < NPOINTS; i++
)
{
data = input++;
coef = coefficient;
sum = 0;
tmp1 = *data;
if ( data==initial )
{
data =
initial + ( NTAPS - 1 );
}
else
{
data--;
}
tmp2 = *coef++;
for ( j = 1; j < NTAPS;
j++ )
{
sum += tmp1 *
tmp2;
tmp1 = *data;
if ( data ==
initial )
{
data = initial + ( NTAPS - 1 );
}
else
{
data--;
}
tmp2 = *coef++;
}
sum += tmp1 *
tmp2;
*output++ = sum;
}
}
3. use of "arrays":
void fir( int input[], /* input sample array of NTAPS points */
int output[], /* output array of NPOINTS points */
int coefficient[] /* array of NTAPS coefficients */
)
{
int i;
int j;
int sum;
for ( i = 0; i < NPOINTS;
i++ )
{
sum = 0;
for ( j = 0; j <
NTAPS; j++ )
{
if (
( i - j ) < 0 )
{
sum += input[i-j+NTAPS] * coefficient[j];
}
else
{
sum += input[i-j] * coefficient[j];
}
}
output[i] = sum;
}
}
4. use of "arrays with a swap":
void fir( int input[], /* input sample array of
NTAPS points */
int output[], /* output array of NPOINTS points */
int coefficient[] /* array of NTAPS coefficients */
)
{
int i;
int j;
int sum, tmp1, tmp2;
for ( i = 0; i < NPOINTS; i++
)
{
sum = 0;
tmp1 = input[i];
tmp2 =
coefficient[0];
for (j = 1; j <
NTAPS; j++)
{
sum +=
tmp1 * tmp2;
if ( ( i
- j ) < 0 )
{
tmp1 = input[i-j+NTAPS];
}
else
{
tmp1 = input[i-j];
}
tmp2 =
coefficient[j];
}
sum += tmp1 * tmp2;
output[i] = sum;
}
}
The following table lists execution time
improvements achieved by sco over
different implementations of the
256-tap FIR filter processing 64 points
 256-tap FIR filter
processing 64 points |
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