[racket-dev] hex decoding?

On 06/11/2013 04:33 PM, Matthias Felleisen wrote:
>
>   db/private/mysql/connection.rkt does not export the function, otherwise you could.
I don't understand this.  I'd like to make the function available to 
users somewhere - are you saying that's bad?
>
>
> On Jun 11, 2013, at 4:26 PM, David Vanderson wrote:
>
>> Thank you Stephen and Tony for your examples.  I found the following private function in db/private/mysql/connection.rkt:
>>
>> (define (hex-string->bytes s)
>>   (define (hex-digit->int c)
>>     (let ([c (char->integer c)])
>>       (cond [(<= (char->integer #\0) c (char->integer #\9))
>>              (- c (char->integer #\0))]
>>             [(<= (char->integer #\a) c (char->integer #\f))
>>              (+ 10 (- c (char->integer #\a)))]
>>             [(<= (char->integer #\A) c (char->integer #\F))
>>              (+ 10 (- c (char->integer #\A)))])))
>>   (unless (and (string? s) (even? (string-length s))
>>                (regexp-match? #rx"[0-9a-zA-Z]*" s))
>>     (raise-type-error 'hex-string->bytes
>>                       "string containing an even number of hexadecimal digits" s))
>>   (let* ([c (quotient (string-length s) 2)]
>>          [b (make-bytes c)])
>>     (for ([i (in-range c)])
>>       (let ([high (hex-digit->int (string-ref s (+ i i)))]
>>             [low  (hex-digit->int (string-ref s (+ i i 1)))])
>>         (bytes-set! b i (+ (arithmetic-shift high 4) low))))
>>     b))
>>
>>
>> Can this function be exported?  I'm willing to make a patch with docs and tests - is file/sha1 the right place?
>>
>> Thanks,
>> Dave
>>
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>