math/big: don't scan past a binary exponent if not accepted syntactically
TBR adonovan
Change-Id: I842cbc855dbd560f65e76c9a557dff1a22c5d610
Reviewed-on: https://go-review.googlesource.com/4882
Reviewed-by: Robert Griesemer <gri@golang.org>
diff --git a/src/math/big/floatconv.go b/src/math/big/floatconv.go
index 04f9a4e..a857fa65 100644
--- a/src/math/big/floatconv.go
+++ b/src/math/big/floatconv.go
@@ -46,11 +46,12 @@
// digits = digit { digit } .
// digit = "0" ... "9" | "a" ... "z" | "A" ... "Z" .
//
-// The base argument must be 0 or a value between 2 through MaxBase.
+// The base argument must be 0, 2, 10, or 16. Providing an invalid base
+// argument will lead to a run-time panic.
//
// For base 0, the number prefix determines the actual base: A prefix of
// ``0x'' or ``0X'' selects base 16, and a ``0b'' or ``0B'' prefix selects
-// base 2; otherwise, the actual base is 10 and no prefix is permitted.
+// base 2; otherwise, the actual base is 10 and no prefix is accepted.
// The octal prefix ``0'' is not supported.
//
// A "p" exponent indicates power of 2 for the exponent; for instance "1.2p3"
@@ -75,7 +76,7 @@
// exponent
var exp int64
var ebase int
- exp, ebase, err = scanExponent(r)
+ exp, ebase, err = scanExponent(r, true)
if err != nil {
return
}
diff --git a/src/math/big/ratconv.go b/src/math/big/ratconv.go
index da4915e..778077b 100644
--- a/src/math/big/ratconv.go
+++ b/src/math/big/ratconv.go
@@ -78,9 +78,8 @@
// exponent
var exp int64
- var ebase int
- exp, ebase, err = scanExponent(r)
- if ebase == 2 || err != nil {
+ exp, _, err = scanExponent(r, false)
+ if err != nil {
return nil, false
}
@@ -115,7 +114,17 @@
return z, true
}
-func scanExponent(r io.ByteScanner) (exp int64, base int, err error) {
+// scanExponent scans the longest possible prefix of r representing a decimal
+// ('e', 'E') or binary ('p') exponent, if any. It returns the exponent, the
+// exponent base (10 or 2), or a read or syntax error, if any.
+//
+// exponent = ( "E" | "e" | "p" ) [ sign ] digits .
+// sign = "+" | "-" .
+// digits = digit { digit } .
+// digit = "0" ... "9" .
+//
+// A binary exponent is only permitted if binExpOk is set.
+func scanExponent(r io.ByteScanner, binExpOk bool) (exp int64, base int, err error) {
base = 10
var ch byte
@@ -130,7 +139,11 @@
case 'e', 'E':
// ok
case 'p':
- base = 2
+ if binExpOk {
+ base = 2
+ break // ok
+ }
+ fallthrough // binary exponent not permitted
default:
r.UnreadByte()
return // no exponent; same as e0
