From: trevor_hansen <trevor_hansen@e59a4935-1847-0410-ae03-e826735625c1>
Date: Fri, 11 Jun 2010 01:01:39 +0000 (+0000)
Subject: Adds a simplification rule to replace BVANDS with zeroes at the front with a CONCAT.
X-Git-Url: https://git.unchartedbackwaters.co.uk/w/?a=commitdiff_plain;h=77655ad2b2a3a01c9cd0ed80180d8b23b9c8615e;p=francis%2Fstp.git

Adds a simplification rule to replace BVANDS with zeroes at the front with a CONCAT.


git-svn-id: https://stp-fast-prover.svn.sourceforge.net/svnroot/stp-fast-prover/trunk/stp@829 e59a4935-1847-0410-ae03-e826735625c1
---

diff --git a/src/simplifier/simplifier.cpp b/src/simplifier/simplifier.cpp
index 838c0f7..100fef0 100644
--- a/src/simplifier/simplifier.cpp
+++ b/src/simplifier/simplifier.cpp
@@ -469,6 +469,7 @@ namespace BEEV
     return output;
   } //end of SimplifyAtomicFormula()
 
+
   // number of constant bits in the most significant places.
   int mostSignificantConstants(const ASTNode& n)
   {
@@ -524,6 +525,18 @@ namespace BEEV
     	return false;
     }
 
+    int numberOfLeadingZeroes(const ASTNode& n)
+    {
+  	  int c = mostSignificantConstants( n);
+  	  if (c<=0)
+  		  return 0;
+
+  	  for (int i =0; i < c;i++)
+  		  if (getConstantBit(n,i)!=0)
+  			  return i;
+  	  return c;
+    }
+
 
     bool unsignedGreaterThan(const ASTNode& n1, const ASTNode& n2)
     {
@@ -2392,6 +2405,32 @@ namespace BEEV
           						zero);
           				assert(BVTypeCheck(output));
           			}
+
+
+          			// If the leading bits are zero. Replace it by a concat with zero.
+          			int i;
+          			if (output.GetKind() == BVAND && output.Degree() ==2 && ((i=numberOfLeadingZeroes(output[0])) > 0) )
+          			{
+					// i contains the number of leading zeroes.
+						output = nf->CreateTerm(BVCONCAT,
+								output.GetValueWidth(),
+								_bm->CreateZeroConst(i),
+								nf->CreateTerm(BVAND, output.GetValueWidth() - i,
+								nf->CreateTerm(BVEXTRACT,
+										output.GetValueWidth() - i,
+										output[0],
+										_bm->CreateBVConst(32,output.GetValueWidth() - i-1),
+										_bm->CreateBVConst(32,0)
+										),
+								nf->CreateTerm(BVEXTRACT,
+										output.GetValueWidth() - i,
+										output[1],
+										_bm->CreateBVConst(32,output.GetValueWidth() - i-1),
+										_bm->CreateBVConst(32,0)
+										))
+								);
+						assert(BVTypeCheck(output));
+          			}
           		}
           break;
         }