Re: [Sbcl-devel] Re: Re: [Sbcl-help] MD5 Mysteries ....

[Nathan F. <fr...@cs...>]

On Sat, May 14, 2005 at 12:17:40AM +0200, R. Mattes wrote:
> How is that? Doesn't a base-string consist entirely of base-chars (with
> code-points <= 127)? How _can_ i construct an array of characters with
> code-point <= 127 that has a different internal representation?

(Assuming a SB-UNICODEd SBCL) You do this all the time, simply by
typing strings at the REPL:

CL-USER> (type-of "DAD")
(SIMPLE-ARRAY CHARACTER (3))

Such a string has a layout that looks roughly like:

[tag] [length] [00 00 00 44] [00 00 00 41] [00 00 00 44] [00 00 00 00]

where [...] is a 32-bit quantity, with values written in hexadecimal
when necessary.  If you instead said something like:

CL-USER (type-of (coerce "DAD" '(simple-array base-char (3)))
(SIMPLE-BASE-STRING (3))

The memory layout of such a string would look like:

[tag] [length] [44 41 44 00]

which is more like what you are expecting.  But that doesn't mean that
you get to pun such a string into being a sequence of bytes like C.

> I _hope_ i don't sound stubborn but i somehow miss to see the half-
> bakedness of this interface [1]. Somehow i expect 
> 
>  (sb-md5:md5sum-sequence "Blah") to act equivalent to
>  (sb:md5sum-sequence (string-to-octets "Blah" :encoding :default))
> 
> but i might be wrong.

Don't expect; read the documentation! :)

CL-USER> (documentation 'sb-md5:md5sum-sequence 'function)
"Calculate the MD5 message-digest of data bounded by START and END
in SEQUENCE , which must be a vector with element-type (UNSIGNED-BYTE
8)."
-- 
Nathan | From Man's effeminate slackness it begins.  --Paradise Lost

The last good thing written in C was Franz Schubert's Symphony Number 9.
                                               --Erwin Dieterich