// TODO(austin): Maybe add to bignum in more general form
func ratToString(rat *bignum.Rational) string {
n, dnat := rat.Value()
d := bignum.MakeInt(false, dnat)
w, frac := n.QuoRem(d)
out := w.String()
if frac.IsZero() {
return out
}
r := frac.Abs()
r = r.Mul(bignum.Nat(1e6))
dec, tail := r.DivMod(dnat)
// Round last digit
if tail.Cmp(dnat.Div(bignum.Nat(2))) >= 0 {
dec = dec.Add(bignum.Nat(1))
}
// Strip zeros
ten := bignum.Nat(10)
for !dec.IsZero() {
dec2, r2 := dec.DivMod(ten)
if !r2.IsZero() {
break
}
dec = dec2
}
out += "." + dec.String()
return out
}
// a.convertTo(t) converts the value of the analyzed expression a,
// which must be a constant, ideal number, to a new analyzed
// expression with a constant value of type t.
//
// TODO(austin) Rename to resolveIdeal or something?
func (a *expr) convertTo(t Type) *expr {
if !a.t.isIdeal() {
log.Crashf("attempted to convert from %v, expected ideal", a.t)
}
var rat *bignum.Rational
// XXX(Spec) The spec says "It is erroneous".
//
// It is an error to assign a value with a non-zero fractional
// part to an integer, or if the assignment would overflow or
// underflow, or in general if the value cannot be represented
// by the type of the variable.
switch a.t {
case IdealFloatType:
rat = a.asIdealFloat()()
if t.isInteger() && !rat.IsInt() {
a.diag("constant %v truncated to integer", ratToString(rat))
return nil
}
case IdealIntType:
i := a.asIdealInt()()
rat = bignum.MakeRat(i, bignum.Nat(1))
default:
log.Crashf("unexpected ideal type %v", a.t)
}
// Check bounds
if t, ok := t.lit().(BoundedType); ok {
if rat.Cmp(t.minVal()) < 0 {
a.diag("constant %v underflows %v", ratToString(rat), t)
return nil
}
if rat.Cmp(t.maxVal()) > 0 {
a.diag("constant %v overflows %v", ratToString(rat), t)
return nil
}
}
// Convert rat to type t.
res := a.newExpr(t, a.desc)
switch t := t.lit().(type) {
case *uintType:
n, d := rat.Value()
f := n.Quo(bignum.MakeInt(false, d))
v := f.Abs().Value()
res.eval = func(*Thread) uint64 { return v }
case *intType:
n, d := rat.Value()
f := n.Quo(bignum.MakeInt(false, d))
v := f.Value()
res.eval = func(*Thread) int64 { return v }
case *idealIntType:
n, d := rat.Value()
f := n.Quo(bignum.MakeInt(false, d))
res.eval = func() *bignum.Integer { return f }
case *floatType:
n, d := rat.Value()
v := float64(n.Value()) / float64(d.Value())
res.eval = func(*Thread) float64 { return v }
case *idealFloatType:
res.eval = func() *bignum.Rational { return rat }
default:
log.Crashf("cannot convert to type %T", t)
}
return res
}