in reply to Re^26: Interleaving bytes in a string quickly
in thread Interleaving bytes in a string quickly

Sorry, but I'm still gonna disagree with you.

An overflow isn't a change in meaning, it's a change in value.

No. The value (bitpattern) hasn't changed one iota. Only the meaning assigned to that value: 

#! perl -slw
use 5.010;
use strict;
use Inline C => Config => BUILD_NOISY => 1;
use Inline C => <<'END_C',  NAME => '_junk', CLEAN_AFTER_BUILD => 0;

void doit( SV *dummy ) {
    int i = -1;
    unsigned int j = i;

    printf( "i: %d : %4x\n", i, i );
    printf( "j: %u : %4x\n", j, j );
}
END_C

doit( 1 );
__END__
C:\test>junk
...
i: -1 : ffffffff
j: 4294967295 : ffffffff

[download]

And there is no "overflow" involved, as the full build log below dmonstrates. No warnings. Which makes it the perfect analogy for two identical strings of bytes, with differing setting of the SVf_UTF8 flag. Same value, different meaning. To Perl.

something I have agreed with.

Where? I've looked at the whole thread again and this:

It doesn't actually do the encoding,.

is the first time I can see.

but it's the only way you'll get the encoded version implicitly.

I've been pointing out right from the very beginning, that I'm not interested in getting "the encoded version", because there will never be an encoded version. Because I'm never going to call encode() on binary data that can never be safely or logically treated as any form of unicode. 

C:\test>junk
Starting Build Preprocess Stage
Finished Build Preprocess Stage

Starting Build Parse Stage
Finished Build Parse Stage

Starting Build Glue 1 Stage
Finished Build Glue 1 Stage

Starting Build Glue 2 Stage
Finished Build Glue 2 Stage

Starting Build Glue 3 Stage
Finished Build Glue 3 Stage

Starting Build Compile Stage
  Starting "perl Makefile.PL" Stage
Writing Makefile for _junk
  Finished "perl Makefile.PL" Stage

  Starting "make" Stage

Microsoft (R) Program Maintenance Utility Version 9.00.21022.08
Copyright (C) Microsoft Corporation.  All rights reserved.

        C:\Perl64\bin\perl.exe C:\Perl64\lib\ExtUtils\xsubpp  -typemap
+ C:\Perl64\lib\ExtUtils\typemap  _junk
        cl -c  -IC:/test  -nologo -GF -W3 -MD -Zi -DNDEBUG -Ox -GL -Wp
+64 -fp:precise -DWIN32 -D_CONSOLE -DNO
cl : Command line warning D9035 : option 'Wp64' has been deprecated an
+d will be removed in a future release
cl : Command line warning D9035 : option 'Wp64' has been deprecated an
+d will be removed in a future release
_junk.c
Running Mkbootstrap for _junk ()
        C:\Perl64\bin\perl.exe -MExtUtils::Command -e "chmod" -- 644 _
+junk.bs
        C:\Perl64\bin\perl.exe -MExtUtils::Mksymlists  -e "Mksymlists(
+'NAME'=>\"_junk\", 'DLBASE' => '_junk'
        link -out:blib\arch\auto\_junk\_junk.dll -dll -nologo -nodefau
+ltlib -debug -opt:ref,icf -ltcg  -libp
   Creating library blib\arch\auto\_junk\_junk.lib and object blib\arc
+h\auto\_junk\_junk.exp
Generating code
Finished generating code
        if exist blib\arch\auto\_junk\_junk.dll.manifest mt -nologo -m
+anifest blib\arch\auto\_junk\_junk.dll
        if exist blib\arch\auto\_junk\_junk.dll.manifest del blib\arch
+\auto\_junk\_junk.dll.manifest
        C:\Perl64\bin\perl.exe -MExtUtils::Command -e "chmod" -- 755 b
+lib\arch\auto\_junk\_junk.dll
        C:\Perl64\bin\perl.exe -MExtUtils::Command -e "cp" -- _junk.bs
+ blib\arch\auto\_junk\_junk.bs
        C:\Perl64\bin\perl.exe -MExtUtils::Command -e "chmod" -- 644 b
+lib\arch\auto\_junk\_junk.bs
  Finished "make" Stage

  Starting "make install" Stage

Microsoft (R) Program Maintenance Utility Version 9.00.21022.08
Copyright (C) Microsoft Corporation.  All rights reserved.

Files found in blib\arch: installing files in blib\lib into architectu
+re dependent library tree
Installing C:\test\_Inline\lib\auto\_junk\_junk.dll
Installing C:\test\_Inline\lib\auto\_junk\_junk.exp
Installing C:\test\_Inline\lib\auto\_junk\_junk.lib
Installing C:\test\_Inline\lib\auto\_junk\_junk.pdb
  Finished "make install" Stage

  Starting Cleaning Up Stage
  Finished Cleaning Up Stage

Finished Build Compile Stage

i: -1 : ffffffff
j: 4294967295 : ffffffff

[download]
Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
"Science is about questioning the status quo. Questioning authority".
In the absence of evidence, opinion is indistinguishable from prejudice.
"I'd rather go naked than blow up my ass"

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Re^28: Interleaving bytes in a string quickly
by ikegami (Patriarch) on Mar 01, 2010 at 17:14 UTC

    Only the meaning assigned to that value:

    Your demo actually shows that there is no change in meaning. It's %d or %u that controls what gets displayed, so %d and %u is what gives the value meaning.

    I will grant you that there is no change in value for some purposes. i==j is true, so the value is the same as far as == is concerned. However, i<5 == j<5 is false, so the value isn't different as far as < is concerned.

    It's still moot, though, since 8-bit strings are a proper subset of 32/64-bit strings.

    I've been pointing out right from the very beginning, that I'm not interested in getting "the encoded version"

    Exactly, and SvPVX can return the encoded version. At least without the limitation you added a couple of posts ago.

    that can never be safely or logically treated as any form of unicode.

    I don't know why you keep bringing up unicode.

[reply]
      <iand SvPVX can return the encoded version.

      Gaaaaaaaaah! No it can't. It just returns a pointer to some memory. It places no interpretation upon what it is that memory. And neither does my code.

      I don't know why you keep bringing up unicode.

      Look again. Prior to the quoted post, I mentioned it once, and you mentioned it once.

      That aside, isn't utf-8 a "form of unicode."?

      Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
      "Science is about questioning the status quo. Questioning authority".
      In the absence of evidence, opinion is indistinguishable from prejudice.
[reply]

        It places no interpretation upon what it is that memory.

        I know! You've said this a dozen times already. And what format is that pointed memory in? You only guaranteed the format in a node 20 deep or so.

        It places no interpretation upon what it is that memory.

        That aside, isn't utf-8 a "form of unicode."?

        Look again.

        Ah yes, you only said "codepoint", not "unicode". That usually mean "unicode codepoints", but you didn't imply any character semantics.

        That aside, isn't utf-8 a "form of unicode."?

        Unicode is a character set. You're clearly not dealing with characters.

        UTF-8 is a storage format. Typically, it's used to encode unicode characters, but Perl uses it internally to encode 32-bit or 64-bit integers (depending on your build). Those integers may be codepoints, but that applies to UTF8=0 strings too.

[reply]

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