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Re: Conversion to unibyte, magic latin-1?

From: Stefan Monnier
Subject: Re: Conversion to unibyte, magic latin-1?
Date: Sat, 04 May 2019 18:53:46 -0400
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/27.0.50 (gnu/linux)

>     (secure-hash 'sha256 (concat [#x52 #xbc #xdd #x9e]))
>     "cfdc1612961dc873079178b92bf0aafaa6bd33731cbaa60841eef163f85074e8"

(concat [#x52 #xbc #xdd #x9e]) takes the character codes you specified
and interprets them as unicode chars rather than as bytes.  So that's
the origin of your problem.

You want to use (unibyte-string #x52 #xbc #xdd #x9e) instead.

> `string-make-unibyte':

Don't.  This will just paper over problems.

If you have a multibyte string (i.e. a sequence of characters) and you
need to convert it to a unibyte string (i.e. a sequence of bytes), then
you want to use `encode-coding-string` where the CODING-SYSTEM indicates
how to convert each char to a corresponding sequence of bytes.

> with a few obvious encodings, but no luck:

`raw-text` is not an obvious encoding.
Encoding with `raw-text` only works in a meaningful way on sequences of
chars where the chars are themselves bytes (these are the char codes
0-127 and #x3fff80-#x3fffff).

> This works, but I'm confused... why does latin-1 work but raw-text or
> binary doesn't?

latin-1 will work in some cases, but only by accident.
Better go back to the origin of the problem (why do you end up with
a multibyte string when what you wanted was a unibyte string).


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