math/big: clearer semantics for Float.Scan
Change-Id: I72e8389ec080be8a0119f98df898de6f5510fa4d
Reviewed-on: https://go-review.googlesource.com/7693
Reviewed-by: Alan Donovan <adonovan@google.com>
diff --git a/src/math/big/floatconv.go b/src/math/big/floatconv.go
index f6a78b7..8905718 100644
--- a/src/math/big/floatconv.go
+++ b/src/math/big/floatconv.go
@@ -63,12 +63,21 @@
// be binary, if present (an "e" or "E" exponent indicator cannot be
// distinguished from a mantissa digit).
//
+// The returned *Float f is nil and the value of z is valid but not
+// defined if an error is reported.
+//
// BUG(gri) The Float.Scan signature conflicts with Scan(s fmt.ScanState, ch rune) error.
func (z *Float) Scan(r io.ByteScanner, base int) (f *Float, b int, err error) {
- if z.prec == 0 {
- z.prec = 64
+ prec := z.prec
+ if prec == 0 {
+ prec = 64
}
+ // NaNs ignore sign, mantissa, and exponent so we can set
+ // them below while having a valid value for z in case of
+ // errors.
+ z.SetNaN()
+
// sign
z.neg, err = scanSign(r)
if err != nil {
@@ -90,13 +99,12 @@
return
}
- // set result
- f = z
-
// special-case 0
if len(z.mant) == 0 {
+ z.prec = prec
z.acc = Exact
z.form = zero
+ f = z
return
}
// len(z.mant) > 0
@@ -141,10 +149,11 @@
// apply 2**exp2
if MinExp <= exp2 && exp2 <= MaxExp {
+ z.prec = prec
z.form = finite
z.exp = int32(exp2)
+ f = z
} else {
- f = nil
err = fmt.Errorf("exponent overflow")
return
}
@@ -175,8 +184,8 @@
}
// Parse is like z.Scan(r, base), but instead of reading from an
-// io.ByteScanner, it parses the string s. An error is returned if
-// the string contains invalid or trailing bytes not belonging to
+// io.ByteScanner, it parses the string s. An error is also returned
+// if the string contains invalid or trailing bytes not belonging to
// the number.
func (z *Float) Parse(s string, base int) (f *Float, b int, err error) {
r := strings.NewReader(s)
