// Uint64 returns the numeric value of this literal truncated to fit
// an unsigned 64-bit integer.
//
func (l *Literal) Uint64() uint64 {
switch x := l.Value; x.Kind() {
case exact.Int:
if u, ok := exact.Uint64Val(x); ok {
return u
}
return 0
case exact.Float:
f, _ := exact.Float64Val(x)
return uint64(f)
}
panic(fmt.Sprintf("unexpected literal value: %T", l.Value))
}
func (check *checker) shift(x, y *operand, op token.Token) {
untypedx := isUntyped(x.typ)
// The lhs must be of integer type or be representable
// as an integer; otherwise the shift has no chance.
if !isInteger(x.typ) && (!untypedx || !isRepresentableConst(x.val, nil, UntypedInt)) {
check.invalidOp(x.pos(), "shifted operand %s must be integer", x)
x.mode = invalid
return
}
// spec: "The right operand in a shift expression must have unsigned
// integer type or be an untyped constant that can be converted to
// unsigned integer type."
switch {
case isInteger(y.typ) && isUnsigned(y.typ):
// nothing to do
case isUntyped(y.typ):
check.convertUntyped(y, Typ[UntypedInt])
if y.mode == invalid {
x.mode = invalid
return
}
default:
check.invalidOp(y.pos(), "shift count %s must be unsigned integer", y)
x.mode = invalid
return
}
if x.mode == constant {
if y.mode == constant {
if untypedx {
x.typ = Typ[UntypedInt]
}
// rhs must be within reasonable bounds
const stupidShift = 1024
s, ok := exact.Uint64Val(y.val)
if !ok || s >= stupidShift {
check.invalidOp(y.pos(), "%s: stupid shift", y)
x.mode = invalid
return
}
// everything's ok
x.val = exact.Shift(x.val, op, uint(s))
return
}
// non-constant shift with constant lhs
if untypedx {
// spec: "If the left operand of a non-constant shift expression is
// an untyped constant, the type of the constant is what it would be
// if the shift expression were replaced by its left operand alone;
// the type is int if it cannot be determined from the context (for
// instance, if the shift expression is an operand in a comparison
// against an untyped constant)".
// Delay operand checking until we know the final type:
// The lhs expression must be in the untyped map, mark
// the entry as lhs shift operand.
if info, ok := check.untyped[x.expr]; ok {
info.isLhs = true
check.untyped[x.expr] = info
} else {
unreachable()
}
// keep x's type
x.mode = value
return
}
}
// non-constant shift - lhs must be an integer
if !isInteger(x.typ) {
check.invalidOp(x.pos(), "shifted operand %s must be integer", x)
x.mode = invalid
return
}
// non-constant shift
x.mode = value
}