fix: constants involving exponents

This puts through a simple fix for constant values involving exponents.
Again, this was a simple aliasing bug.

pkg/corset/expression.go

@@ -270,7 +270,11 @@ func (e *Exp) AsConstant() *big.Int {
 	pow := e.Pow.AsConstant()
 	// Check if can evaluate
 	if arg != nil && pow != nil {
-		return arg.Exp(arg, pow, nil)
+		var res big.Int
+		// Compute exponent
+		res.Exp(arg, pow, nil)
+		// Done
+		return &res
 	}
 	//
 	return nil
@@ -605,7 +609,14 @@ type Normalise struct{ Arg Expr }
 // AsConstant attempts to evaluate this expression as a constant (signed) value.
 // If this expression is not constant, then nil is returned.
 func (e *Normalise) AsConstant() *big.Int {
-	// FIXME: we could do better here.
+	if arg := e.Arg.AsConstant(); arg != nil {
+		if arg.Cmp(big.NewInt(0)) != 0 {
+			return big.NewInt(1)
+		}
+		// zero
+		return arg
+	}
+	//
 	return nil
 }
 

pkg/corset/translator.go

@@ -449,7 +449,7 @@ func (t *translator) translateExpressionInModule(expr Expr, module string, shift
 	case *Shift:
 		return t.translateShiftInModule(e, module, shift)
 	case *VariableAccess:
-		return t.translateVariableAccessInModule(e, module, shift)
+		return t.translateVariableAccessInModule(e, shift)
 	default:
 		return nil, t.srcmap.SyntaxErrors(expr, "unknown expression encountered during translation")
 	}
@@ -519,16 +519,19 @@ func (t *translator) translateShiftInModule(expr *Shift, module string, shift in
 	return t.translateExpressionInModule(expr.Arg, module, shift+int(constant.Int64()))
 }
 
-func (t *translator) translateVariableAccessInModule(expr *VariableAccess, module string,
-	shift int) (hir.Expr, []SyntaxError) {
+func (t *translator) translateVariableAccessInModule(expr *VariableAccess, shift int) (hir.Expr, []SyntaxError) {
 	if binding, ok := expr.Binding().(*ColumnBinding); ok {
 		// Lookup column binding
 		cinfo := t.env.Column(binding.module, expr.Name())
 		// Done
 		return &hir.ColumnAccess{Column: cinfo.ColumnId(), Shift: shift}, nil
 	} else if binding, ok := expr.Binding().(*ConstantBinding); ok {
 		// Just fill in the constant.
-		return t.translateExpressionInModule(binding.value, module, shift)
+		var constant fr.Element
+		// Initialise field from bigint
+		constant.SetBigInt(binding.value.AsConstant())
+		//
+		return &hir.Constant{Val: constant}, nil
 	}
 	// error
 	return nil, t.srcmap.SyntaxErrors(expr, "unbound variable")

pkg/test/valid_corset_test.go

@@ -103,6 +103,10 @@ func Test_Constant_09(t *testing.T) {
 	Check(t, false, "constant_09")
 }
 
+func Test_Constant_10(t *testing.T) {
+	Check(t, false, "constant_10")
+}
+
 // ===================================================================
 // Alias Tests
 // ===================================================================
@@ -818,9 +822,9 @@ func TestSlow_Stp(t *testing.T) {
 	Check(t, true, "stp")
 }
 
-/* func TestSlow_Mmio(t *testing.T) {
+func TestSlow_Mmio(t *testing.T) {
 	Check(t, true, "mmio")
-} */
+}
 
 // ===================================================================
 // Test Helpers

testdata/constant_10.accepts

@@ -0,0 +1,5 @@
+{ "X": [], "Y": [] }
+{ "X": [0], "Y": [0] }
+{ "X": [16], "Y": [1] }
+{ "X": [32], "Y": [2] }
+{ "X": [64], "Y": [4] }

testdata/constant_10.lisp

@@ -0,0 +1,7 @@
+(defcolumns (X :@loob) Y)
+(defconst
+  N 4
+  TWO_N (^ 2 N))
+
+;; X == Y * 2^n
+(defconstraint c1 () (- X (* Y TWO_N)))

testdata/constant_10.rejects

@@ -0,0 +1,18 @@
+{ "X": [1], "Y": [0] }
+{ "X": [1], "Y": [1] }
+{ "X": [2], "Y": [1] }
+{ "X": [3], "Y": [1] }
+{ "X": [4], "Y": [1] }
+{ "X": [5], "Y": [1] }
+{ "X": [6], "Y": [1] }
+{ "X": [7], "Y": [1] }
+{ "X": [8], "Y": [1] }
+{ "X": [9], "Y": [1] }
+{ "X": [10], "Y": [1] }
+{ "X": [11], "Y": [1] }
+{ "X": [12], "Y": [1] }
+{ "X": [13], "Y": [1] }
+{ "X": [14], "Y": [1] }
+{ "X": [15], "Y": [1] }
+{ "X": [17], "Y": [1] }
+{ "X": [18], "Y": [1] }