math/big: only permit bases 2, 10, 16 when scanning number w/ "decimal" point
TBR adonovan
Change-Id: I4fd694101c2cf1c0c39bf73d16cab18502742dd9
Reviewed-on: https://go-review.googlesource.com/4881
Reviewed-by: Robert Griesemer <gri@golang.org>
diff --git a/src/math/big/natconv.go b/src/math/big/natconv.go
index e094d22..b5c3773 100644
--- a/src/math/big/natconv.go
+++ b/src/math/big/natconv.go
@@ -8,6 +8,7 @@
import (
"errors"
+ "fmt"
"io"
"math"
"sync"
@@ -50,7 +51,7 @@
// scan scans the number corresponding to the longest possible prefix
// from r representing an unsigned number in a given conversion base.
// It returns the corresponding natural number res, the actual base b,
-// a digit count, and an error err, if any.
+// a digit count, and a read or syntax error err, if any.
//
// number = [ prefix ] mantissa .
// prefix = "0" [ "x" | "X" | "b" | "B" ] .
@@ -58,12 +59,15 @@
// digits = digit { digit } .
// digit = "0" ... "9" | "a" ... "z" | "A" ... "Z" .
//
-// The base argument must be 0 or a value between 0 through MaxBase.
+// Unless fracOk is set, the base argument must be 0 or a value between
+// 2 through MaxBase. If fracOk is set, the base argument must be one of
+// 0, 2, 10, or 16. Providing an invalid base argument leads to a run-
+// time panic.
//
// For base 0, the number prefix determines the actual base: A prefix of
// ``0x'' or ``0X'' selects base 16; if fracOk is not set, the ``0'' prefix
// selects base 8, and a ``0b'' or ``0B'' prefix selects base 2. Otherwise
-// the selected base is 10 and no prefix is permitted.
+// the selected base is 10 and no prefix is accepted.
//
// If fracOk is set, an octal prefix is ignored (a leading ``0'' simply
// stands for a zero digit), and a period followed by a fractional part
@@ -73,13 +77,15 @@
// A result digit count > 0 corresponds to the number of (non-prefix) digits
// parsed. A digit count <= 0 indicates the presence of a period (if fracOk
// is set, only), and -count is the number of fractional digits found.
-// In this case, the value of the scanned number is res * 10**count.
+// In this case, the actual value of the scanned number is res * b**count.
//
func (z nat) scan(r io.ByteScanner, base int, fracOk bool) (res nat, b, count int, err error) {
// reject illegal bases
- if base != 0 && base < 2 || base > MaxBase {
- err = errors.New("illegal number base")
- return
+ baseOk := base == 0 ||
+ !fracOk && 2 <= base && base <= MaxBase ||
+ fracOk && (base == 2 || base == 10 || base == 16)
+ if !baseOk {
+ panic(fmt.Sprintf("illegal number base %d", base))
}
// one char look-ahead
diff --git a/src/math/big/natconv_test.go b/src/math/big/natconv_test.go
index d4c3fb4..f321fbc 100644
--- a/src/math/big/natconv_test.go
+++ b/src/math/big/natconv_test.go
@@ -98,10 +98,6 @@
ok bool // expected success
next rune // next character (or 0, if at EOF)
}{
- // error: illegal base
- {base: -1},
- {base: 37},
-
// error: no mantissa
{},
{s: "?"},
@@ -114,7 +110,7 @@
// error: incorrect use of decimal point
{s: ".0"},
{s: ".0", base: 10},
- {s: ".", base: 1},
+ {s: ".", base: 0},
{s: "0x.0"},
// no errors
