math/big: remove []byte/string conversions

This removes some of the []byte/string conversions currently
existing in the (un)marshaling methods of Int and Rat.

For Int we introduce a new function (*Int).setFromScanner() essentially
implementing the SetString method being given an io.ByteScanner instead
of a string. So we can handle the string case in (*Int).SetString with
a *strings.Reader and the []byte case in (*Int).UnmarshalText() with a
*bytes.Reader now avoiding the []byte/string conversion here.

For Rat we introduce a new function (*Rat).marshal() essentially
implementing the String method outputting []byte instead of string.
Using this new function and the same formatting rules as in
(*Rat).RatString we can implement (*Rat).MarshalText() without
the []byte/string conversion it used to have.

Change-Id: Ic5ef246c1582c428a40f214b95a16671ef0a06d9
Reviewed-on: https://go-review.googlesource.com/65950
Reviewed-by: Robert Griesemer <gri@golang.org>
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

1 files changed, 4 insertions, 2 deletions

diff --git a/src/math/big/ratmarsh.go b/src/math/big/ratmarsh.go
index b82e8d4ae8..fbc7b6002d 100644
--- a/src/math/big/ratmarsh.go
+++ b/src/math/big/ratmarsh.go
@@ -59,8 +59,10 @@ func (z *Rat) GobDecode(buf []byte) error {
 
 // MarshalText implements the encoding.TextMarshaler interface.
 func (x *Rat) MarshalText() (text []byte, err error) {
-	// TODO(gri): get rid of the []byte/string conversion
-	return []byte(x.RatString()), nil
+	if x.IsInt() {
+		return x.a.MarshalText()
+	}
+	return x.marshal(), nil
 }
 
 // UnmarshalText implements the encoding.TextUnmarshaler interface.