musicdsp.org source code archive - WSInf

Look ahead limiting (click this to go back to the index)
References : Posted by Wilfried Welti
Notes :
use add_value with all values which enter the look-ahead area,
and remove_value with all value which leave this area. to get
the maximum value in the look-ahead area, use get_max_value.
in the very beginning initialize the table with zeroes.
If you always want to know the maximum amplitude in
your look-ahead area, the thing becomes a sorting
problem. very primitive approach using a look-up table
Code :
void lookup_add(unsigned section, unsigned size, unsigned value)
{
if (section==value)
lookup[section]++;
else
{
size >>= 1;
if (value>section)
{
lookup[section]++;
lookup_add(section+size,size,value);
}
else
lookup_add(section-size,size,value);
}
}
void lookup_remove(unsigned section, unsigned size, unsigned value)
{
if (section==value)
lookup[section]--;
else
{
size >>= 1;
if (value>section)
{
lookup[section]--;
lookup_remove(section+size,size,value);
}
else
lookup_remove(section-size,size,value);
}
}
unsigned lookup_getmax(unsigned section, unsigned size)
{
unsigned max = lookup[section] ? section : 0;
size >>= 1;
if (size)
if (max)
{
max = lookup_getmax((section+size),size);
if (!max) max=section;
}
else
max = lookup_getmax((section-size),size);
return max;
}
void add_value(unsigned value)
{
lookup_add(LOOKUP_VALUES>>1, LOOKUP_VALUES>>1, value);
}
void remove_value(unsigned value)
{
lookup_remove(LOOKUP_VALUES>>1, LOOKUP_VALUES>>1, value);
}
unsigned get_max_value()
{
return lookup_getmax(LOOKUP_VALUES>>1, LOOKUP_VALUES>>1);
}