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synthesize the special case of compare with 0.

This commit is contained in:
steve 2001-08-31 22:59:48 +00:00
parent e79a371f76
commit 3fbbd4080a
1 changed files with 48 additions and 1 deletions
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49
expr_synth.cc
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@ -17,7 +17,7 @@
* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
*/
#if !defined(WINNT) && !defined(macintosh)
#ident "$Id: expr_synth.cc,v 1.25 2001/08/05 02:49:07 steve Exp $"
#ident "$Id: expr_synth.cc,v 1.26 2001/08/31 22:59:48 steve Exp $"
#endif
# include "config.h"
@ -139,6 +139,50 @@ NetNet* NetEBBits::synthesize(Design*des)
NetNet* NetEBComp::synthesize(Design*des)
{
NetEConst*lcon = reinterpret_cast<NetEConst*>(left_);
NetEConst*rcon = reinterpret_cast<NetEConst*>(right_);
/* Handle the special case where one of the inputs is constant
0. We can use an OR gate to do the comparison. Synthesize
the non-const side as normal, then or(nor) the signals
together to get result. */
if ((rcon && (rcon->value() == verinum(0UL,rcon->expr_width())))
|| (lcon && (lcon->value() == verinum(0UL,lcon->expr_width())))) {
NetNet*lsig = rcon
? left_->synthesize(des)
: right_->synthesize(des);
NetScope*scope = lsig->scope();
assert(scope);
string path = des->local_symbol(scope->name());
NetNet*osig = new NetNet(scope, path, NetNet::IMPLICIT, 1);
osig->local_flag(true);
NetLogic*gate;
switch (op_) {
case 'e':
case 'E':
gate = new NetLogic(scope, des->local_symbol(path),
lsig->pin_count()+1, NetLogic::NOR);
break;
case 'n':
case 'N':
gate = new NetLogic(scope, des->local_symbol(path),
lsig->pin_count()+1, NetLogic::OR);
break;
default:
assert(0);
}
connect(gate->pin(0), osig->pin(0));
for (unsigned idx = 0 ; idx < lsig->pin_count() ; idx += 1)
connect(gate->pin(idx+1), lsig->pin(idx));
des->add_node(gate);
return osig;
}
NetNet*lsig = left_->synthesize(des);
NetNet*rsig = right_->synthesize(des);
@ -509,6 +553,9 @@ NetNet* NetESignal::synthesize(Design*des)
/*
* $Log: expr_synth.cc,v $
* Revision 1.26 2001/08/31 22:59:48 steve
* synthesize the special case of compare with 0.
*
* Revision 1.25 2001/08/05 02:49:07 steve
* Properly synthesize part selects.
*