Add support for log() arithmetic functional operator.

PiperOrigin-RevId: 695530002

interpreter/operator_arithmetic.go

@@ -162,6 +162,34 @@ func evalLn(_ model.IUnaryExpression, obj result.Value) (result.Value, error) {
 	return result.New(math.Log(val))
 }
 
+// Log(argument Decimal) Decimal
+// https://cql.hl7.org/09-b-cqlreference.html#log
+func evalLog(_ model.IBinaryExpression, lObj, rObj result.Value) (result.Value, error) {
+	if result.IsNull(lObj) || result.IsNull(rObj) {
+		return result.New(nil)
+	}
+	x, base, err := applyToValues(lObj, rObj, result.ToFloat64)
+	if err != nil {
+		return result.Value{}, err
+	}
+	val, err := log(x, base)
+	if err != nil {
+		return result.New(nil)
+	}
+	return result.New(val)
+}
+
+// log returns the logarithm of val with given base.
+func log(val, base float64) (float64, error) {
+	if val <= 0 || base <= 0 {
+		return 0.0, fmt.Errorf("internal error - log base %v for val %v, all values	must be greater than 0", base, val)
+	}
+	if base == 1 {
+		return 0.0, fmt.Errorf("internal error - log base %v is undefined", base)
+	}
+	return math.Log(val) / math.Log(base), nil
+}
+
 // op(left Integer, right Integer) Integer
 // https://cql.hl7.org/09-b-cqlreference.html#add
 // https://cql.hl7.org/09-b-cqlreference.html#subtract

interpreter/operator_dispatcher.go

@@ -671,6 +671,13 @@ func (i *interpreter) binaryOverloads(m model.IBinaryExpression) ([]convert.Over
 				Result:   evalArithmeticQuantity,
 			},
 		}, nil
+	case *model.Log:
+		return []convert.Overload[evalBinarySignature]{
+			{
+				Operands: []types.IType{types.Decimal, types.Decimal},
+				Result:   evalLog,
+			},
+		}, nil
 	case *model.And, *model.Or, *model.XOr, *model.Implies:
 		return []convert.Overload[evalBinarySignature]{
 			{

model/model.go

@@ -946,6 +946,9 @@ type Modulo struct{ *BinaryExpression }
 // Power ELM Expression https://cql.hl7.org/04-logicalspecification.html#power
 type Power struct{ *BinaryExpression }
 
+// Log ELM Expression https://cql.hl7.org/04-logicalspecification.html#log.
+type Log struct{ *BinaryExpression }
+
 // TruncatedDivide ELM Expression https://cql.hl7.org/04-logicalspecification.html#truncateddivide
 type TruncatedDivide struct{ *BinaryExpression }
 
@@ -1194,6 +1197,9 @@ func (a *Floor) GetName() string { return "Floor" }
 // GetName returns the name of the system operator.
 func (a *Ln) GetName() string { return "Ln" }
 
+// GetName returns the name of the system operator.
+func (a *Log) GetName() string { return "Log" }
+
 // GetName returns the name of the system operator.
 func (a *Precision) GetName() string { return "Precision" }
 

parser/operators.go

@@ -716,6 +716,17 @@ func (p *Parser) loadSystemOperators() error {
 				}
 			},
 		},
+		{
+			name:     "Log",
+			operands: [][]types.IType{{types.Decimal, types.Decimal}},
+			model: func() model.IExpression {
+				return &model.Log{
+					BinaryExpression: &model.BinaryExpression{
+						Expression: model.ResultType(types.Decimal),
+					},
+				}
+			},
+		},
 		{
 			name:     "Negate",
 			operands: [][]types.IType{{types.Integer}},

parser/operators_test.go

@@ -525,6 +525,19 @@ func TestBuiltInFunctions(t *testing.T) {
 				},
 			},
 		},
+		{
+			name: "Arithmetic Log",
+			cql:  "Log(1.0, 10.0)",
+			want: &model.Log{
+				BinaryExpression: &model.BinaryExpression{
+					Operands: []model.IExpression{
+						model.NewLiteral("1.0", types.Decimal),
+						model.NewLiteral("10.0", types.Decimal),
+					},
+					Expression: model.ResultType(types.Decimal),
+				},
+			},
+		},
 		{
 			name: "Arithmetic Precision",
 			cql:  "Precision(@2014)",

tests/enginetests/operator_arithmetic_test.go

@@ -520,6 +520,102 @@ func TestLn(t *testing.T) {
 	}
 }
 
+func TestLog(t *testing.T) {
+	tests := []struct {
+		name       string
+		cql        string
+		wantModel  model.IExpression
+		wantResult result.Value
+	}{
+		{
+			name: "Decimal",
+			cql:  "Log(1.0, 10.0)",
+			wantModel: &model.Log{
+				BinaryExpression: &model.BinaryExpression{
+					Operands: []model.IExpression{
+						model.NewLiteral("1.0", types.Decimal),
+						model.NewLiteral("10.0", types.Decimal),
+					},
+					Expression: model.ResultType(types.Decimal),
+				},
+			},
+			wantResult: newOrFatal(t, 0.0),
+		},
+		{
+			name:       "Negative value",
+			cql:        "Log(-2.1, 10.0)",
+			wantResult: newOrFatal(t, nil),
+		},
+		{
+			name:       "Negative base",
+			cql:        "Log(2.1, -10.0)",
+			wantResult: newOrFatal(t, nil),
+		},
+		{
+			name:       "Zero value",
+			cql:        "Log(0.0, 10.0)",
+			wantResult: newOrFatal(t, nil),
+		},
+		{
+			name:       "Zero base",
+			cql:        "Log(2.1, 0.0)",
+			wantResult: newOrFatal(t, nil),
+		},
+		{
+			name:       "Logarithm of 0.125 with base 2",
+			cql:        "Log(0.125, 2.0)",
+			wantResult: newOrFatal(t, -3.0),
+		},
+		{
+			name:       "Integer of 16 with base 2",
+			cql:        "Log(16, 2)",
+			wantResult: newOrFatal(t, 4.0),
+		},
+		{
+			name:       "Minimum Integer value",
+			cql:        "Log(-2147483648, 10)",
+			wantResult: newOrFatal(t, nil),
+		},
+		{
+			name:       "Maximum Integer value",
+			cql:        "Round(Log(2147483647, 10), 3)",
+			wantResult: newOrFatal(t, 9.332),
+		},
+		{
+			name:       "Null value",
+			cql:        "Log(null as Decimal, 10)",
+			wantResult: newOrFatal(t, nil),
+		},
+		{
+			name:       "Null base",
+			cql:        "Log(1.0, null as Decimal)",
+			wantResult: newOrFatal(t, nil),
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			p := newFHIRParser(t)
+			parsedLibs, err := p.Libraries(context.Background(), wrapInLib(t, tc.cql), parser.Config{})
+			if err != nil {
+				t.Fatalf("Parse returned unexpected error: %v", err)
+			}
+			if diff := cmp.Diff(tc.wantModel, getTESTRESULTModel(t, parsedLibs)); tc.wantModel != nil && diff != "" {
+				t.Errorf("Parse diff (-want +got):\n%s", diff)
+			}
+
+			results, err := interpreter.Eval(context.Background(), parsedLibs, defaultInterpreterConfig(t, p))
+			if err != nil {
+				t.Fatalf("Eval returned unexpected error: %v", err)
+			}
+
+			if diff := cmp.Diff(tc.wantResult, getTESTRESULT(t, results), protocmp.Transform()); diff != "" {
+				t.Errorf("Eval diff (-want +got)\n%v", diff)
+			}
+		})
+	}
+}
+
 func TestPrecision(t *testing.T) {
 	tests := []struct {
 		name       string

tests/spectests/exclusions/exclusions.go

@@ -59,7 +59,6 @@ func XMLTestFileExclusionDefinitions() map[string]XMLTestFileExclusions {
 			GroupExcludes: []string{
 				// TODO: b/342061715 - unsupported operators.
 				"HighBoundary",
-				"Log",
 				"LowBoundary",
 			},
 			NamesExcludes: []string{