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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>
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@ -46,11 +46,12 @@ func (z *Float) SetString(s string) (*Float, bool) {
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// digits = digit { digit } .
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// digit = "0" ... "9" | "a" ... "z" | "A" ... "Z" .
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//
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// The base argument must be 0 or a value between 2 through MaxBase.
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// The base argument must be 0, 2, 10, or 16. Providing an invalid base
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// argument will lead to a run-time panic.
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//
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// For base 0, the number prefix determines the actual base: A prefix of
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// ``0x'' or ``0X'' selects base 16, and a ``0b'' or ``0B'' prefix selects
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// base 2; otherwise, the actual base is 10 and no prefix is permitted.
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// base 2; otherwise, the actual base is 10 and no prefix is accepted.
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// The octal prefix ``0'' is not supported.
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//
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// A "p" exponent indicates power of 2 for the exponent; for instance "1.2p3"
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@ -75,7 +76,7 @@ func (z *Float) Scan(r io.ByteScanner, base int) (f *Float, b int, err error) {
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// exponent
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var exp int64
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var ebase int
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exp, ebase, err = scanExponent(r)
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exp, ebase, err = scanExponent(r, true)
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if err != nil {
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return
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}
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@ -78,9 +78,8 @@ func (z *Rat) SetString(s string) (*Rat, bool) {
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// exponent
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var exp int64
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var ebase int
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exp, ebase, err = scanExponent(r)
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if ebase == 2 || err != nil {
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exp, _, err = scanExponent(r, false)
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if err != nil {
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return nil, false
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}
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@ -115,7 +114,17 @@ func (z *Rat) SetString(s string) (*Rat, bool) {
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return z, true
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}
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func scanExponent(r io.ByteScanner) (exp int64, base int, err error) {
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// scanExponent scans the longest possible prefix of r representing a decimal
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// ('e', 'E') or binary ('p') exponent, if any. It returns the exponent, the
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// exponent base (10 or 2), or a read or syntax error, if any.
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//
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// exponent = ( "E" | "e" | "p" ) [ sign ] digits .
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// sign = "+" | "-" .
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// digits = digit { digit } .
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// digit = "0" ... "9" .
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//
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// A binary exponent is only permitted if binExpOk is set.
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func scanExponent(r io.ByteScanner, binExpOk bool) (exp int64, base int, err error) {
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base = 10
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var ch byte
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@ -130,7 +139,11 @@ func scanExponent(r io.ByteScanner) (exp int64, base int, err error) {
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case 'e', 'E':
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// ok
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case 'p':
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base = 2
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if binExpOk {
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base = 2
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break // ok
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}
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fallthrough // binary exponent not permitted
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default:
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r.UnreadByte()
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return // no exponent; same as e0
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