Say I have this snippet of code....
{
var no_overlap = true;//( pd.algorithm == match_types.TwoGroupsNoOver )
//|| ( pd.algorithm == match_types.TwoGroupsPrimeNoOver );
//var prime = ( pd.algorithm == match_types.TwoGroupsPrime )
// || ( pd.algorithm == match_types.TwoGroupsPrimeNoOver );
var g;
var masks = []
var index = [];
var n = 0;
var m = 0;
for( g = 0; g < pd.groups.length; g++ ) {
simple_masks.push( ExpandMods( pd.groups[g].mode_mod, pd.groups[g].masks ) )
index.push(0);
}
do {
var composite = 0;
for( g = 0; g < pd.groups.length; g++ ) {
masks[g] = simple_masks[g][index[g]];
if( no_overlap )
if( composite & masks[g] ) {
break;
}
composite |= masks[g];
}
if( g < pd.groups.length ) {
g++; // add 1 to g... so 'this' gets incremented
// this faulted, so next iterate.
for( var h = g; h < pd.groups.length; h++ ){
index[h] = 0; // reset all the following counters
}
}
else
composite_masks.push(composite);
// iterate combination set.
index[g-1]++;
while( g > 0 && ( index[g-1] >= simple_masks[g-1].length ) ) {
if( g > 1 ) // don't reset 0.
index[g-1] = 0;
if( --g > 0 )
index[g-1]++;
}
if( !g ){
if( index[0] >= simple_masks[0].length )
break;
}
}while(1);
}
This is all algorithmic; no expression calls a function, so a lot of things
should be easiliy identifiable as unchanging.
pd.groups.length
for instance comes from 'pd.groups' which will never change during the
duration of the above code, and that array within it also would not change,
would the length for that be read once at the start?
I've seen compiled code from C (where many compilers apparently assume that
everything is at least somewhat volatile (apparently) and reload values of
partial expressions even though that same value was just computed in the
previous section. Especially where the number of available scratch
registers is plentiful (as opposed to only 4-6) ?
I would hope that I could write visually appealing code like the above and
have the guts of the actual code generation do all the clever work; maybe
it is a lot of work to do a pattern match in an AST and find all
sub-expressions that are exactly the same to coalesce into a single
access...
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