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/********************* */
/*! \file BitVectorsAndArrays.java
** \verbatim
** Top contributors (to current version):
** Pat Hawks, Andres Noetzli
** This file is part of the CVC4 project.
** Copyright (c) 2009-2020 by the authors listed in the file AUTHORS
** in the top-level source directory) and their institutional affiliations.
** All rights reserved. See the file COPYING in the top-level source
** directory for licensing information.\endverbatim
**
** \brief [[ Add one-line brief description here ]]
**
** [[ Add lengthier description here ]]
** \todo document this file
**/
import static org.junit.Assert.assertEquals;
import edu.stanford.CVC4.*;
import org.junit.Before;
import org.junit.Test;
public class BitVectorsAndArrays {
static {
System.loadLibrary("cvc4jni");
}
ExprManager em;
SmtEngine smt;
@Before
public void initialize() {
em = new ExprManager();
smt = new SmtEngine(em);
}
@Test
public void evaluatesExpression() {
smt.setOption("produce-models", new SExpr(true)); // Produce Models
smt.setOption("output-language", new SExpr("smtlib")); // output-language
smt.setLogic("QF_AUFBV"); // Set the logic
// Consider the following code (where size is some previously defined constant):
//
// Assert (current_array[0] > 0);
// for (unsigned i = 1; i < k; ++i) {
// current_array[i] = 2 * current_array[i - 1];
// Assert (current_array[i-1] < current_array[i]);
// }
//
// We want to check whether the assertion in the body of the for loop holds
// throughout the loop.
// Setting up the problem parameters
int k = 4; // number of unrollings (should be a power of 2)
int index_size = log2(k); // size of the index
// Types
Type elementType = em.mkBitVectorType(32);
Type indexType = em.mkBitVectorType(index_size);
Type arrayType = em.mkArrayType(indexType, elementType);
// Variables
Expr current_array = em.mkVar("current_array", arrayType);
// Making a bit-vector constant
Expr zero = em.mkConst(new BitVector(index_size, 0));
// Asserting that current_array[0] > 0
Expr current_array0 = em.mkExpr(Kind.SELECT, current_array, zero);
Expr current_array0_gt_0 = em.mkExpr(Kind.BITVECTOR_SGT, current_array0, em.mkConst(new BitVector(32, 0)));
smt.assertFormula(current_array0_gt_0);
// Building the assertions in the loop unrolling
Expr index = em.mkConst(new BitVector(index_size, 0));
Expr old_current = em.mkExpr(Kind.SELECT, current_array, index);
Expr two = em.mkConst(new BitVector(32, 2));
vectorExpr assertions = new vectorExpr(em);
for (int i = 1; i < k; ++i) {
index = em.mkConst(
new BitVector(index_size, new edu.stanford.CVC4.Integer(i)));
Expr new_current = em.mkExpr(Kind.BITVECTOR_MULT, two, old_current);
// current[i] = 2 * current[i-1]
current_array = em.mkExpr(Kind.STORE, current_array, index, new_current);
// current[i-1] < current [i]
Expr current_slt_new_current = em.mkExpr(Kind.BITVECTOR_SLT, old_current, new_current);
assertions.add(current_slt_new_current);
old_current = em.mkExpr(Kind.SELECT, current_array, index);
}
Expr query = em.mkExpr(Kind.NOT, em.mkExpr(Kind.AND, assertions));
smt.assertFormula(query);
Result.Sat expect = Result.Sat.SAT;
Result.Sat actual = smt.checkSat(em.mkConst(true)).isSat();
assertEquals(expect, actual);
}
private static int log2(int n) {
return (int) Math.round(Math.log(n) / Math.log(2));
}
}
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