reflect: add support for Type.Bits()

src/reflect/type.go

@@ -164,8 +164,15 @@ func (t Type) Field(i int) StructField {
 	panic("unimplemented: (reflect.Type).Field()")
 }
 
+// Bits returns the number of bits that this type uses. It is only valid for
+// arithmetic types (integers, floats, and complex numbers). For other types, it
+// will panic.
 func (t Type) Bits() int {
-	panic("unimplemented: (reflect.Type).Bits()")
+	kind := t.Kind()
+	if kind >= Int && kind <= Complex128 {
+		return int(t.Size()) * 8
+	}
+	panic(TypeError{"Bits"})
 }
 
 func (t Type) Len() int {
@@ -213,3 +220,17 @@ type StructField struct {
 	Name string
 	Type Type
 }
+
+// TypeError is the error that is used in a panic when invoking a method on a
+// type that is not applicable to that type.
+type TypeError struct {
+	Method string
+}
+
+func (e *TypeError) Error() string {
+	return "reflect: call of reflect.Type." + e.Method + " on invalid type"
+}
+
+func align(offset uintptr, alignment uintptr) uintptr {
+	return (offset + alignment - 1) &^ (alignment - 1)
+}

testdata/reflect.go

@@ -92,18 +92,25 @@ func main() {
 
 	// test sizes
 	println("\nsizes:")
-	println("int8", int(reflect.TypeOf(int8(0)).Size()))
-	println("int16", int(reflect.TypeOf(int16(0)).Size()))
-	println("int32", int(reflect.TypeOf(int32(0)).Size()))
-	println("int64", int(reflect.TypeOf(int64(0)).Size()))
-	println("uint8", int(reflect.TypeOf(uint8(0)).Size()))
-	println("uint16", int(reflect.TypeOf(uint16(0)).Size()))
-	println("uint32", int(reflect.TypeOf(uint32(0)).Size()))
-	println("uint64", int(reflect.TypeOf(uint64(0)).Size()))
-	println("float32", int(reflect.TypeOf(float32(0)).Size()))
-	println("float64", int(reflect.TypeOf(float64(0)).Size()))
-	println("complex64", int(reflect.TypeOf(complex64(0)).Size()))
-	println("complex128", int(reflect.TypeOf(complex128(0)).Size()))
+	for _, tc := range []struct {
+		name string
+		rt   reflect.Type
+	}{
+		{"int8", reflect.TypeOf(int8(0))},
+		{"int16", reflect.TypeOf(int16(0))},
+		{"int32", reflect.TypeOf(int32(0))},
+		{"int64", reflect.TypeOf(int64(0))},
+		{"uint8", reflect.TypeOf(uint8(0))},
+		{"uint16", reflect.TypeOf(uint16(0))},
+		{"uint32", reflect.TypeOf(uint32(0))},
+		{"uint64", reflect.TypeOf(uint64(0))},
+		{"float32", reflect.TypeOf(float32(0))},
+		{"float64", reflect.TypeOf(float64(0))},
+		{"complex64", reflect.TypeOf(complex64(0))},
+		{"complex128", reflect.TypeOf(complex128(0))},
+	} {
+		println(tc.name, int(tc.rt.Size()), tc.rt.Bits())
+	}
 	assertSize(reflect.TypeOf(uintptr(0)).Size() == unsafe.Sizeof(uintptr(0)), "uintptr")
 	assertSize(reflect.TypeOf("").Size() == unsafe.Sizeof(""), "string")
 	assertSize(reflect.TypeOf(new(int)).Size() == unsafe.Sizeof(new(int)), "*int")

testdata/reflect.txt

@@ -222,15 +222,15 @@ reflect type: struct
   struct
 
 sizes:
-int8 1
-int16 2
-int32 4
-int64 8
-uint8 1
-uint16 2
-uint32 4
-uint64 8
-float32 4
-float64 8
-complex64 8
-complex128 16
+int8 1 8
+int16 2 16
+int32 4 32
+int64 8 64
+uint8 1 8
+uint16 2 16
+uint32 4 32
+uint64 8 64
+float32 4 32
+float64 8 64
+complex64 8 64
+complex128 16 128