[racket] Best typed/racket representation for bitfield of width 125?

If you type check the file on a 64-bit system like yours, but then ran it
on a 32-bit system, the fixnum range would change, making that number into
a bignum.

Sam
On Sep 6, 2014 8:37 AM, "John Clements" <johnbclements at gmail.com> wrote:

> Is this a bug, or just a known limitation of typed racket? It looks like a
> fixnum can be up to 2^61, but the type checker for integer literals doesn't
> like them. This program:
>
> #lang typed/racket
>
> (require racket/fixnum)
>
> (define (ensure-fixnum i)
>   (cond [(fixnum? i) i]
>         [else (error 'ensure-fixnum)]))
>
> (fixnum? 281474976710656) ;; -> #t
> (: i Fixnum)
> (define i (ensure-fixnum 281474976710656))
>
> works fine, but requires the ensure-fixnum, because the type checker does
> not believe that the literal 281474976710656 lives in fixnum.
>
> You can also see this at the top level, using (:print-type 281474976710656)
>
> Is this a bug, or is this just a known compromise to simplify the
> type-checker's portability and numeric tower?
>
> John
>
>
>
>
> On Thu, Sep 4, 2014 at 12:35 PM, Vincent St-Amour <stamourv at ccs.neu.edu>
> wrote:
>
>> Would an fxvector of length 5 (to account for the tag bits) work?
>>
>> If all you're doing is bitwise ops and comparisons, it should be easy to
>> convince TR that you're staying within fixnum range.
>>
>> Vincent
>>
>>
>>
>>
>> At Thu, 4 Sep 2014 10:45:48 -0700,
>> John Clements wrote:
>> >
>> > [1  <multipart/alternative (7bit)>]
>> > [1.1  <text/plain; UTF-8 (quoted-printable)>]
>> > I want to represent a bitfield of 125 bits, using typed racket. I’ll be
>> > combining them using bitwise operations, and checking for zero-ness. I
>> > think that’s about it.
>> >
>> > I could just use type Integer, but it seems like that would impose
>> > additional checking, since the type system doesn’t know the size.  In
>> > untyped racket I used a vector of four integers in the range 0-2^32, but
>> > those don’t fit in typed Racket’s “Fixnum” because it uses a signed
>> > representation (and indeed, untyped racket may have been falling prey to
>> > the same problem. Perhaps I should break it up into four integers in the
>> > range 0-2^31? That seems weird, but maybe that’s my best choice? Or… I
>> > could use a byte string.
>> >
>> > Apologies if I’m missing something in the docs, here; I’ve spent a few
>> > minutes searching, without turning anything up.
>> >
>> > Thanks for any advice,
>> >
>> > John
>> > [1.2  <text/html; UTF-8 (quoted-printable)>]
>> >
>> > [2  <text/plain; us-ascii (7bit)>]
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>
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