Re: [Help-smalltalk] Interesting Float to Fraction conversion

[J Pfersich]

Thanks, that works.

At 08:25 AM 10/27/2006 +0900, Paolo Bonzini wrote:
> With the included patch, I get:
>
> st> x := 1.14474205677314q-13.
> st> x asFraction printNl.
> st> (x asFraction - x) printNl!
> 2931673387916173/25609903738315777422401732608
> 1.40129846432481707092372958329q-45
>
> That's pretty good.
>
> Thanks,
>
> Paolo
>
>
> --- orig/kernel/Float.st
> +++ mod/kernel/Float.st
> @@ -221,7 +221,7 @@ asFraction
>      "Convert the receiver into a fraction with a good (but undefined)
>       approximation"
>
> -    | a x n2 d2 n1 d1 n0 d0 eps abs |
> +    | a x n2 d2 n1 d1 n0 d0 eps abs gcd |
>
>      self checkCoercion.
>
> @@ -232,8 +232,8 @@ asFraction
>
>      n1  := d0 := 0.
>      n0  := d1 := 1.
> -    abs := self abs.
> -    eps := self class epsilon * 1024.  "Number out of a hat"
> +    abs := self abs timesTwoPower: self exponent negated.
> +    eps := self class epsilon.
>      x   := abs.
>
>      [   a := x truncated.
> @@ -245,6 +245,14 @@ asFraction
>             ((self coerce: n0) / (self coerce: d0) - abs) abs < eps ]
>      ]   whileFalse.
>
> +    self abs < 1
> +       ifTrue: [ d0 := d0 * (2 raisedToInteger: self exponent negated) ]
> +       ifFalse: [ n0 := n0 * (2 raisedToInteger: self exponent) ].
> +
> +    gcd := n0 gcd: d0.
> +    n0 := n0 quo: gcd.
> +    d0 := d0 quo: gcd.
> +
>      ^Fraction
>         numerator: (self < 0 ifTrue: [ n0 negated ] ifFalse: [ n0 ])
>         denominator: d0