src/pkg/exp/eval/util.go

// Copyright 2009 The Go Authors.  All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package eval

import (
	"bignum"
)

// 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
}