reflect: implement Type.Overflow* functions

They're already implemented for the Value equivalents. But since Go
1.23, such methods also exist for reflect.Type.

2 files changed, 108 insertions, 1 deletions

diff --git a/src/reflect/all_test.go b/src/reflect/all_test.go
index 4c2fcc48b..436bc0034 100644
--- a/src/reflect/all_test.go
+++ b/src/reflect/all_test.go
@@ -4897,7 +4897,7 @@ func TestComparable(t *testing.T) {
 	}
 }
 
-func TestOverflow(t *testing.T) {
+func TestValueOverflow(t *testing.T) {
 	if ovf := V(float64(0)).OverflowFloat(1e300); ovf {
 		t.Errorf("%v wrongly overflows float64", 1e300)
 	}
@@ -4936,6 +4936,45 @@ func TestOverflow(t *testing.T) {
 	}
 }
 
+func TestTypeOverflow(t *testing.T) {
+	if ovf := TypeFor[float64]().OverflowFloat(1e300); ovf {
+		t.Errorf("%v wrongly overflows float64", 1e300)
+	}
+
+	maxFloat32 := float64((1<<24 - 1) << (127 - 23))
+	if ovf := TypeFor[float32]().OverflowFloat(maxFloat32); ovf {
+		t.Errorf("%v wrongly overflows float32", maxFloat32)
+	}
+	ovfFloat32 := float64((1<<24-1)<<(127-23) + 1<<(127-52))
+	if ovf := TypeFor[float32]().OverflowFloat(ovfFloat32); !ovf {
+		t.Errorf("%v should overflow float32", ovfFloat32)
+	}
+	if ovf := TypeFor[float32]().OverflowFloat(-ovfFloat32); !ovf {
+		t.Errorf("%v should overflow float32", -ovfFloat32)
+	}
+
+	maxInt32 := int64(0x7fffffff)
+	if ovf := TypeFor[int32]().OverflowInt(maxInt32); ovf {
+		t.Errorf("%v wrongly overflows int32", maxInt32)
+	}
+	if ovf := TypeFor[int32]().OverflowInt(-1 << 31); ovf {
+		t.Errorf("%v wrongly overflows int32", -int64(1)<<31)
+	}
+	ovfInt32 := int64(1 << 31)
+	if ovf := TypeFor[int32]().OverflowInt(ovfInt32); !ovf {
+		t.Errorf("%v should overflow int32", ovfInt32)
+	}
+
+	maxUint32 := uint64(0xffffffff)
+	if ovf := TypeFor[uint32]().OverflowUint(maxUint32); ovf {
+		t.Errorf("%v wrongly overflows uint32", maxUint32)
+	}
+	ovfUint32 := uint64(1 << 32)
+	if ovf := TypeFor[uint32]().OverflowUint(ovfUint32); !ovf {
+		t.Errorf("%v should overflow uint32", ovfUint32)
+	}
+}
+
 /*
 
 func checkSameType(t *testing.T, x Type, y any) {
diff --git a/src/reflect/type.go b/src/reflect/type.go
index aa84c77a2..5dd59b329 100644
--- a/src/reflect/type.go
+++ b/src/reflect/type.go
@@ -392,6 +392,22 @@ type Type interface {
 	// It panics if the type's Kind is not Func.
 	// It panics if i is not in the range [0, NumOut()).
 	Out(i int) Type
+
+	// OverflowComplex reports whether the complex128 x cannot be represented by type t.
+	// It panics if t's Kind is not Complex64 or Complex128.
+	OverflowComplex(x complex128) bool
+
+	// OverflowFloat reports whether the float64 x cannot be represented by type t.
+	// It panics if t's Kind is not Float32 or Float64.
+	OverflowFloat(x float64) bool
+
+	// OverflowInt reports whether the int64 x cannot be represented by type t.
+	// It panics if t's Kind is not Int, Int8, Int16, Int32, or Int64.
+	OverflowInt(x int64) bool
+
+	// OverflowUint reports whether the uint64 x cannot be represented by type t.
+	// It panics if t's Kind is not Uint, Uintptr, Uint8, Uint16, Uint32, or Uint64.
+	OverflowUint(x uint64) bool
 }
 
 // Constants for the 'meta' byte.
@@ -1081,6 +1097,58 @@ func (t rawType) Out(i int) Type {
 	panic("unimplemented: (reflect.Type).Out()")
 }
 
+// OverflowComplex reports whether the complex128 x cannot be represented by type t.
+// It panics if t's Kind is not Complex64 or Complex128.
+func (t rawType) OverflowComplex(x complex128) bool {
+	k := t.Kind()
+	switch k {
+	case Complex64:
+		return overflowFloat32(real(x)) || overflowFloat32(imag(x))
+	case Complex128:
+		return false
+	}
+	panic("reflect: OverflowComplex of non-complex type")
+}
+
+// OverflowFloat reports whether the float64 x cannot be represented by type t.
+// It panics if t's Kind is not Float32 or Float64.
+func (t rawType) OverflowFloat(x float64) bool {
+	k := t.Kind()
+	switch k {
+	case Float32:
+		return overflowFloat32(x)
+	case Float64:
+		return false
+	}
+	panic("reflect: OverflowFloat of non-float type")
+}
+
+// OverflowInt reports whether the int64 x cannot be represented by type t.
+// It panics if t's Kind is not Int, Int8, Int16, Int32, or Int64.
+func (t rawType) OverflowInt(x int64) bool {
+	k := t.Kind()
+	switch k {
+	case Int, Int8, Int16, Int32, Int64:
+		bitSize := t.Size() * 8
+		trunc := (x << (64 - bitSize)) >> (64 - bitSize)
+		return x != trunc
+	}
+	panic("reflect: OverflowInt of non-int type")
+}
+
+// OverflowUint reports whether the uint64 x cannot be represented by type t.
+// It panics if t's Kind is not Uint, Uintptr, Uint8, Uint16, Uint32, or Uint64.
+func (t rawType) OverflowUint(x uint64) bool {
+	k := t.Kind()
+	switch k {
+	case Uint, Uintptr, Uint8, Uint16, Uint32, Uint64:
+		bitSize := t.Size() * 8
+		trunc := (x << (64 - bitSize)) >> (64 - bitSize)
+		return x != trunc
+	}
+	panic("reflect: OverflowUint of non-uint type")
+}
+
 func (t rawType) Method(i int) Method {
 	panic("unimplemented: (reflect.Type).Method()")
 }