feat: add log2 builtin

builtin/builtin.go

@@ -141,6 +141,13 @@ var Builtins = []*Function{
 			return anyType, fmt.Errorf("invalid argument for abs (type %s)", args[0])
 		},
 	},
+	{
+		Name: "log2",
+		Fast: Log2,
+		Validate: func(args []reflect.Type) (reflect.Type, error) {
+			return validateRoundFunc("log2", args)
+		},
+	},
 	{
 		Name: "ceil",
 		Fast: Ceil,

builtin/builtin_test.go

@@ -46,6 +46,8 @@ func TestBuiltin(t *testing.T) {
 		{`abs(-5)`, 5},
 		{`abs(.5)`, .5},
 		{`abs(-.5)`, .5},
+		{`log2(8)`, 3.0},
+		{`log2(0.5)`, -1.0},
 		{`ceil(5.5)`, 6.0},
 		{`ceil(5)`, 5.0},
 		{`floor(5.5)`, 5.0},
@@ -253,6 +255,8 @@ func TestBuiltin_errors(t *testing.T) {
 		{`abs()`, `invalid number of arguments (expected 1, got 0)`},
 		{`abs(1, 2)`, `invalid number of arguments (expected 1, got 2)`},
 		{`abs("foo")`, `invalid argument for abs (type string)`},
+		{`log2()`, `invalid number of arguments (expected 1, got 0)`},
+		{`log2("foo")`, `invalid argument for log2 (type string)`},
 		{`int()`, `invalid number of arguments (expected 1, got 0)`},
 		{`int(1, 2)`, `invalid number of arguments (expected 1, got 2)`},
 		{`float()`, `invalid number of arguments (expected 1, got 0)`},

builtin/lib.go

@@ -115,6 +115,10 @@ func Abs(x any) any {
 	panic(fmt.Sprintf("invalid argument for abs (type %T)", x))
 }
 
+func Log2(x any) any {
+	return math.Log2(Float(x).(float64))
+}
+
 func Ceil(x any) any {
 	switch x := x.(type) {
 	case float32:

docs/language-definition.md

@@ -580,6 +580,14 @@ Returns the absolute value of a number.
 abs(-5) == 5
 ```
 
+### log2(n) {#log2}
+
+Returns the binary logarithm of a number.
+
+```expr
+log2(8) == 3.0
+```
+
 ### ceil(n) {#ceil}
 
 Returns the least integer value greater than or equal to x.