code review 4128049: fmt.Scan: scan binary-exponent floating format, 2.4p-3

fmt.Scan: scan binary-exponent floating format, 2.4p-3

[r, 2011-02-02 18:28:29]

Hello rsc (cc: golang-dev@googlegroups.com),

I'd like you to review this change.

[rog, 2011-02-02 18:34:30]

%b also does binary for integers.

On 2 February 2011 18:28,  <r@golang.org> wrote:
> Reviewers: rsc,
>
> Message:
> Hello rsc (cc: golang-dev@googlegroups.com),
>
> I'd like you to review this change.
>
>
> Description:
> fmt.Scan: scan binary-exponent floating format, 2.4p-3
>
> Please review this at http://codereview.appspot.com/4128049/
>
> Affected files:
>  M src/pkg/fmt/scan.go
>  M src/pkg/fmt/scan_test.go
>
>
> Index: src/pkg/fmt/scan.go
> ===================================================================
> --- a/src/pkg/fmt/scan.go
> +++ b/src/pkg/fmt/scan.go
> @@ -459,7 +459,7 @@
>        hexadecimalDigits = "0123456789aAbBcCdDeEfF"
>        sign              = "+-"
>        period            = "."
> -       exponent          = "eE"
> +       exponent          = "eEp"
>  )
>
>  // getBase returns the numeric base represented by the verb and its digit
> string.
> @@ -617,6 +617,27 @@
>
>  // convertFloat converts the string to a float64value.
>  func (s *ss) convertFloat(str string, n int) float64 {
> +       if p := strings.Index(str, "p"); p >= 0 {
> +               // Atof doesn't handle power-of-2 exponents,
> +               // but they're easy to evaluate.
> +               f, err := strconv.AtofN(str[:p], n)
> +               if err != nil {
> +                       s.error(nil)
> +               }
> +               n, err := strconv.Atoi64(str[p+1:])
> +               if err != nil {
> +                       s.error(nil)
> +               }
> +               for n > 0 {
> +                       f *= 2
> +                       n--
> +               }
> +               for n < 0 {
> +                       f /= 2
> +                       n++
> +               }
> +               return f
> +       }
>        f, err := strconv.AtofN(str, n)
>        if err != nil {
>                s.error(err)
> @@ -747,7 +768,7 @@
>        return s.buf.String()
>  }
>
> -const floatVerbs = "eEfFgGv"
> +const floatVerbs = "beEfFgGv"
>
>  // scanOne scans a single value, deriving the scanner from the type of the
> argument.
>  func (s *ss) scanOne(verb int, field interface{}) {
> Index: src/pkg/fmt/scan_test.go
> ===================================================================
> --- a/src/pkg/fmt/scan_test.go
> +++ b/src/pkg/fmt/scan_test.go
> @@ -160,6 +160,9 @@
>        {"2.3\n", &float64Val, 2.3},
>        {"2.3e1\n", &float32Val, float32(2.3e1)},
>        {"2.3e2\n", &float64Val, 2.3e2},
> +       {"2.3p2\n", &float64Val, 2.3*4},
> +       {"2.3p+2\n", &float64Val, 2.3*4},
> +       {"2.3p-2\n", &float64Val, 2.3/4},
>        {"2.35\n", &stringVal, "2.35"},
>        {"2345678\n", &bytesVal, []byte("2345678")},
>        {"(3.4e1-2i)\n", &complex128Val, 3.4e1 - 2i},
>
>
>

[r2, 2011-02-02 18:36:16]

On Feb 2, 2011, at 10:34 AM, roger peppe wrote:

> %b also does binary for integers.

yes it does.  what is your point?

-rob

[r, 2011-02-02 18:38:30]

Hello rsc, rog, r2 (cc: golang-dev@googlegroups.com),

Please take another look.

[rog, 2011-02-02 18:40:35]

sorry. i'd just assumed that you'd do both meanings of %b in the
same CL.

On 2 February 2011 18:36, Rob 'Commander' Pike <r@google.com> wrote:
>
> On Feb 2, 2011, at 10:34 AM, roger peppe wrote:
>
>> %b also does binary for integers.
>
> yes it does.  what is your point?
>
> -rob
>
>

[rsc, 2011-02-02 20:20:51]

LGTM

http://codereview.appspot.com/4128049/diff/14001/src/pkg/fmt/scan.go
File src/pkg/fmt/scan.go (right):

http://codereview.appspot.com/4128049/diff/14001/src/pkg/fmt/scan.go#newcode625
src/pkg/fmt/scan.go:625: s.error(err)
In this error and the next one, fill in the 
whole string instead of the half that got
passed to the strconv routine:

if e, ok := err.(*strconv.NumError); ok {
    e.Num = str
}
s.error(err)

http://codereview.appspot.com/4128049/diff/14001/src/pkg/fmt/scan.go#newcode627
src/pkg/fmt/scan.go:627: n, err := strconv.Atoi64(str[p+1:])
Use Atoi and then below call math.Ldexp.

[r, 2011-02-02 20:38:51]

*** Submitted as http://code.google.com/p/go/source/detail?r=e389f2d670be ***

fmt.Scan: scan binary-exponent floating format, 2.4p-3

R=rsc, rog, r2
CC=golang-dev
http://codereview.appspot.com/4128049