bug#34873: 27.0.50; Creating unibyte string in emacs modules

bug#34873: 27.0.50; Creating unibyte string in emacs modules

[Evgeny Zajcev]

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There is no possibility to create unibyte strings from emacs modules in
order to create some binary data representation

The only solution for now is to call `make_string` method and then apply
`encode-coding-string' with utf-8 encoding to the result.  But on large
data this became very slow

I used this patch to bypass the conversion steps and it works pretty nice

Ideally I would like to use user-ptr objects as `:data' in image
specification, but solution with `make_data' module method will be suitable
enough

Thanks

Here is the patch I'm currently using:

diff --git a/src/emacs-module.c b/src/emacs-module.c
index 4e2411cb29..500079c257 100644
--- a/src/emacs-module.c
+++ b/src/emacs-module.c
@@ -591,6 +591,19 @@ module_make_string (emacs_env *env, const char *str,
ptrdiff_t length)
                         code_convert_string_norecord (lstr, Qutf_8,
false));
 }

+static emacs_value
+module_make_data (emacs_env *env, const char *str, ptrdiff_t length)
+{
+  MODULE_FUNCTION_BEGIN (module_nil);
+  if (! (0 <= length && length <= STRING_BYTES_BOUND))
+    overflow_error ();
+
+  Lisp_Object lstr = make_uninit_string (length + 1);
+  memcpy (SDATA (lstr), str, length);
+  SDATA (lstr)[length] = 0;
+  return lisp_to_value (env, lstr);
+}
+
 static emacs_value
 module_make_user_ptr (emacs_env *env, emacs_finalizer_function fin, void
*ptr)
 {
@@ -1081,6 +1094,7 @@ initialize_environment (emacs_env *env, struct
emacs_env_private *priv)
   env->make_float = module_make_float;
   env->copy_string_contents = module_copy_string_contents;
   env->make_string = module_make_string;
+  env->make_data = module_make_data;
   env->make_user_ptr = module_make_user_ptr;
   env->get_user_ptr = module_get_user_ptr;
   env->set_user_ptr = module_set_user_ptr;


Configuration:

In GNU Emacs 27.0.50 (build 19, x86_64-pc-linux-gnu, GTK+ Version 3.22.30)
 of 2019-03-15 built on XPS
Repository revision: 020e69d992c98fd852e835c9bd707a8d137090f2
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.11906000
System Description: Ubuntu 18.04.1 LTS

Recent messages:
t
Mark set [2 times]
Auto-saving...
Mark set [2 times]
t
Saving file /home/lg/.emacs.d/*scratch-file*...
Wrote /home/lg/.emacs.d/*scratch-file*
Finding changes in /home/lg/dev/emacs/src/emacs-module.c...done
Saved text until "nv->set_user_ptr = module_set_user_ptr;
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-- 
lg


-- 
lg

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bug#34873: 27.0.50; Creating unibyte string in emacs modules

[Eli Zaretskii]

> From: Evgeny Zajcev <lg.zevlg@gmail.com>
> Date: Fri, 15 Mar 2019 23:52:17 +0300
> 
> There is no possibility to create unibyte strings from emacs modules in order to create some binary data
> representation
> 
> The only solution for now is to call `make_string` method and then apply `encode-coding-string' with utf-8
> encoding to the result.  But on large data this became very slow
> 
> I used this patch to bypass the conversion steps and it works pretty nice
> 
> Ideally I would like to use user-ptr objects as `:data' in image specification, but solution with `make_data'
> module method will be suitable enough

Please explain why you need to create a unibyte string for that.  I
guess what's missing is more details regarding what you are trying to
do (the single sentence above about :data wasn't enough for me), and
how is your module involved in that, in particular why do you need a
module to display an image in Emacs.

bug#34873: 27.0.50; Creating unibyte string in emacs modules

[lg.zevlg]

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16 марта 2019 г., в 8:30, Eli Zaretskii <eliz@gnu.org> написал(а):

>> From: Evgeny Zajcev <lg.zevlg@gmail.com>
>> Date: Fri, 15 Mar 2019 23:52:17 +0300
>> 
>> There is no possibility to create unibyte strings from emacs modules in order to create some binary data
>> representation
>> 
>> The only solution for now is to call `make_string` method and then apply `encode-coding-string' with utf-8
>> encoding to the result.  But on large data this became very slow
>> 
>> I used this patch to bypass the conversion steps and it works pretty nice
>> 
>> Ideally I would like to use user-ptr objects as `:data' in image specification, but solution with `make_data'
>> module method will be suitable enough
> 
> Please explain why you need to create a unibyte string for that.  I
> guess what's missing is more details regarding what you are trying to
> do (the single sentence above about :data wasn't enough for me), and
> how is your module involved in that, in particular why do you need a
> module to display an image in Emacs.

See this thread https://lists.gnu.org/archive/html/emacs-devel/2019-03/msg00465.html

I need this module, because all existing packages to manipulate images are not capable enough for me

—
lg


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bug#34873: 27.0.50; Creating unibyte string in emacs modules

[Eli Zaretskii]

> From: lg.zevlg@gmail.com
> Date: Sat, 16 Mar 2019 11:32:47 +0100
> Cc: 34873@debbugs.gnu.org
> 
>  Please explain why you need to create a unibyte string for that.  I
>  guess what's missing is more details regarding what you are trying to
>  do (the single sentence above about :data wasn't enough for me), and
>  how is your module involved in that, in particular why do you need a
>  module to display an image in Emacs.
> 
> See this thread https://lists.gnu.org/archive/html/emacs-devel/2019-03/msg00465.html

I've read that (I read everything on emacs-devel).  It still doesn't
tell me enough to answer my questions, unfortunately.

> I need this module, because all existing packages to manipulate images are not capable enough for me

Please tell more, if at all possible.  I don't think I understand the
context yet.

bug#34873: 27.0.50; Creating unibyte string in emacs modules

[lg.zevlg]

16 марта 2019 г., в 13:20, Eli Zaretskii <eliz@gnu.org> написал(а):

>> From: lg.zevlg@gmail.com
>> Date: Sat, 16 Mar 2019 11:32:47 +0100
>> Cc: 34873@debbugs.gnu.org
>> 
>> Please explain why you need to create a unibyte string for that.  I
>> guess what's missing is more details regarding what you are trying to
>> do (the single sentence above about :data wasn't enough for me), and
>> how is your module involved in that, in particular why do you need a
>> module to display an image in Emacs.
>> 
>> See this thread https://lists.gnu.org/archive/html/emacs-devel/2019-03/msg00465.html
> 
> I've read that (I read everything on emacs-devel).  It still doesn't
> tell me enough to answer my questions, unfortunately.

Ok, emacs-ffi is emacs module that implements FFI to shared libraries. wand-mode is package that implements ffi bindings (using emacs-ffi module) to libMagickWand and on top of them powerful image editor is written

wand-mode does many trickery on images in very fast fasion, and it needs method to display previews/results in Emacs buffer. Result of image manipulation is raw rgb(a) data that seats in user-ptr available from imagemagick without any copying. I want `create-image’ with :format ‘image/x-rgb to accept this user-ptr as data to make image creation fast

Method proposed by Stefan with make_string/encode-coding-string works, but its speed is far from being usable on big images.  There is no method just to use data as-is to make things fast


—
lg

bug#34873: 27.0.50; Creating unibyte string in emacs modules

[Eli Zaretskii]

> From: lg.zevlg@gmail.com
> Date: Sat, 16 Mar 2019 16:28:05 +0100
> Cc: 34873@debbugs.gnu.org
> 
> wand-mode does many trickery on images in very fast fasion, and it needs method to display previews/results in Emacs buffer. Result of image manipulation is raw rgb(a) data that seats in user-ptr available from imagemagick without any copying. I want `create-image’ with :format ‘image/x-rgb to accept this user-ptr as data to make image creation fast
> 
> Method proposed by Stefan with make_string/encode-coding-string works, but its speed is far from being usable on big images.  There is no method just to use data as-is to make things fast

I'd prefer to provide a way to use user-ptr objects for this purpose,
rather than allow unibyte strings to be created by modules.  The
latter is a slippery slope which I think we should rather avoid.

Can you propose a patch that uses user-ptr instead?

Thanks.

bug#34873: 27.0.50; Creating unibyte string in emacs modules

[Basil L. Contovounesios]

Eli Zaretskii <eliz@gnu.org> writes:

>> From: lg.zevlg@gmail.com
>> Date: Sat, 16 Mar 2019 16:28:05 +0100
>> Cc: 34873@debbugs.gnu.org
>> 
>> wand-mode does many trickery on images in very fast fasion, and it needs
>> method to display previews/results in Emacs buffer. Result of image
>> manipulation is raw rgb(a) data that seats in user-ptr available from
>> imagemagick without any copying. I want `create-image’ with :format
>> ‘image/x-rgb to accept this user-ptr as data to make image creation fast
>> 
>> Method proposed by Stefan with make_string/encode-coding-string works, but its
>> speed is far from being usable on big images.  There is no method just to use
>> data as-is to make things fast
>
> I'd prefer to provide a way to use user-ptr objects for this purpose,
> rather than allow unibyte strings to be created by modules.  The
> latter is a slippery slope which I think we should rather avoid.
>
> Can you propose a patch that uses user-ptr instead?

Sorry if this is a dumb question, but would the functions
unibyte-string, string-to-unibyte, string-as-unibyte et al. be of any
use here?

-- 
Basil

bug#34873: 27.0.50; Creating unibyte string in emacs modules

[Eli Zaretskii]

> From: "Basil L. Contovounesios" <contovob@tcd.ie>
> Cc: <lg.zevlg@gmail.com>,  <34873@debbugs.gnu.org>
> Date: Tue, 07 May 2019 17:55:56 +0100
> 
> Sorry if this is a dumb question, but would the functions
> unibyte-string, string-to-unibyte, string-as-unibyte et al. be of any
> use here?

I'm not sure I follow: how can these functions help writing code in a
module?  A module cannot be written in Lisp, and you cannot call these
functions on a C string, only on a Lisp string.

What am I missing?

bug#34873: 27.0.50; Creating unibyte string in emacs modules

[Basil L. Contovounesios]

Eli Zaretskii <eliz@gnu.org> writes:

>> From: "Basil L. Contovounesios" <contovob@tcd.ie>
>> Cc: <lg.zevlg@gmail.com>,  <34873@debbugs.gnu.org>
>> Date: Tue, 07 May 2019 17:55:56 +0100
>> 
>> Sorry if this is a dumb question, but would the functions
>> unibyte-string, string-to-unibyte, string-as-unibyte et al. be of any
>> use here?
>
> I'm not sure I follow: how can these functions help writing code in a
> module?  A module cannot be written in Lisp, and you cannot call these
> functions on a C string, only on a Lisp string.
>
> What am I missing?

It could be I that is missing something, but AIUI the module API already
provides module_make_string for creating a multibyte Lisp string from a
C string, which can then be passed to one of the aforementioned
functions via module_funcall, no?

In other words, I'm asking whether the aforementioned functions are in
any way a better alternative to the encode-coding-string approach
previously proposed.

Thanks,

-- 
Basil

bug#34873: 27.0.50; Creating unibyte string in emacs modules

[Eli Zaretskii]

> From: "Basil L. Contovounesios" <contovob@tcd.ie>
> Cc: <lg.zevlg@gmail.com>,  <34873@debbugs.gnu.org>
> Date: Tue, 07 May 2019 20:24:48 +0100
> 
> It could be I that is missing something, but AIUI the module API already
> provides module_make_string for creating a multibyte Lisp string from a
> C string, which can then be passed to one of the aforementioned
> functions via module_funcall, no?
> 
> In other words, I'm asking whether the aforementioned functions are in
> any way a better alternative to the encode-coding-string approach
> previously proposed.

Not sure how it would be better, but I don't think I understand the
use case in enough detail.

bug#34873: 27.0.50; Creating unibyte string in emacs modules

[Lars Ingebrigtsen]

Eli Zaretskii <eliz@gnu.org> writes:

> I'd prefer to provide a way to use user-ptr objects for this purpose,
> rather than allow unibyte strings to be created by modules.  The
> latter is a slippery slope which I think we should rather avoid.

In what way are unibyte strings slippery slopes?  They're a standard
part of the Emacs type vocabulary.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

bug#34873: 27.0.50; Creating unibyte string in emacs modules

[Eli Zaretskii]

> From: Lars Ingebrigtsen <larsi@gnus.org>
> Cc: lg.zevlg@gmail.com,  34873@debbugs.gnu.org
> Date: Wed, 26 Aug 2020 12:43:59 +0200
> 
> In what way are unibyte strings slippery slopes?  They're a standard
> part of the Emacs type vocabulary.

They produce incorrect display of non-ASCII characters, for starters.
They also produce unexpected effects when concatenated with multibyte
strings.  They are in general something to avoid because of these and
other subtleties, since many Lisp programmers are unaware of them, and
can easily fall into one of these pitfalls.

In this case AFAIR the request was to use unibyte strings for binary
data, i.e. stuff that is not a string at all, which is one more reason
not to base the implementation on unibyte strings.

bug#34873: 27.0.50; Creating unibyte string in emacs modules

[Lars Ingebrigtsen]

Eli Zaretskii <eliz@gnu.org> writes:

>> In what way are unibyte strings slippery slopes?  They're a standard
>> part of the Emacs type vocabulary.
>
> They produce incorrect display of non-ASCII characters, for starters.
> They also produce unexpected effects when concatenated with multibyte
> strings.  They are in general something to avoid because of these and
> other subtleties, since many Lisp programmers are unaware of them, and
> can easily fall into one of these pitfalls.
>
> In this case AFAIR the request was to use unibyte strings for binary
> data, i.e. stuff that is not a string at all, which is one more reason
> not to base the implementation on unibyte strings.

Yes, the only real reason to use unibyte strings is for binary data, I
thought?  That's the use case in the proposed patch, too.

Just like unibyte buffers are for data, not text, unibyte strings are
for data, not text.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

bug#34873: 27.0.50; Creating unibyte string in emacs modules

[Eli Zaretskii]

> From: Lars Ingebrigtsen <larsi@gnus.org>
> Cc: lg.zevlg@gmail.com,  34873@debbugs.gnu.org
> Date: Thu, 27 Aug 2020 15:04:32 +0200
> 
> > In this case AFAIR the request was to use unibyte strings for binary
> > data, i.e. stuff that is not a string at all, which is one more reason
> > not to base the implementation on unibyte strings.
> 
> Yes, the only real reason to use unibyte strings is for binary data, I
> thought?

No, that's not the use case for unibyte strings.  We have bindat.el
for that.  Unibyte strings is for handling text that was not yet
decoded into the internal representation, or which was encoded before
sending it to an external program or I/O port.

> Just like unibyte buffers are for data, not text, unibyte strings are
> for data, not text.

If that's what you really think, we disagree.  About the only use case
which comes close (though not close enough) to what you describe is
when we hold compressed data in a buffer.

bug#34873: 27.0.50; Creating unibyte string in emacs modules

[Noam Postavsky]

On Thu, 27 Aug 2020 at 09:43, Eli Zaretskii <eliz@gnu.org> wrote:

> > Yes, the only real reason to use unibyte strings is for binary data, I
> > thought?
>
> No, that's not the use case for unibyte strings.  We have bindat.el
> for that.

Quoting from bindat.el commentary: "Encoded (binary) data is stored in
a unibyte string or vector,"
Does that mean that you think binary data should be stored only in vectors?

bug#34873: 27.0.50; Creating unibyte string in emacs modules

[Eli Zaretskii]

> From: Noam Postavsky <npostavs@gmail.com>
> Date: Thu, 27 Aug 2020 10:33:31 -0400
> Cc: Lars Ingebrigtsen <larsi@gnus.org>, 34873@debbugs.gnu.org, lg.zevlg@gmail.com
> 
> Does that mean that you think binary data should be stored only in vectors?

Why would it mean that, I wonder?

bug#34873: 27.0.50; Creating unibyte string in emacs modules

[Noam Postavsky]

On Thu, 27 Aug 2020 at 12:57, Eli Zaretskii <eliz@gnu.org> wrote:

> > Does that mean that you think binary data should be stored only in vectors?
>
> Why would it mean that, I wonder?

You said binary data is not the use case for unibyte strings and
pointed to bindat.el instead. bindat.el uses unibyte strings or
vectors for binary data.

(NOT unibyte strings) AND (unibyte strings OR vectors) => vectors

bug#34873: 27.0.50; Creating unibyte string in emacs modules

[Eli Zaretskii]

> From: Noam Postavsky <npostavs@gmail.com>
> Date: Thu, 27 Aug 2020 13:13:36 -0400
> Cc: Lars Magne Ingebrigtsen <larsi@gnus.org>, 34873@debbugs.gnu.org, lg.zevlg@gmail.com
> 
> On Thu, 27 Aug 2020 at 12:57, Eli Zaretskii <eliz@gnu.org> wrote:
> 
> > > Does that mean that you think binary data should be stored only in vectors?
> >
> > Why would it mean that, I wonder?
> 
> You said binary data is not the use case for unibyte strings and
> pointed to bindat.el instead. bindat.el uses unibyte strings or
> vectors for binary data.
> 
> (NOT unibyte strings) AND (unibyte strings OR vectors) => vectors

I don't see how it follows.  You are reading into what I wrote
something I didn't mean.  The underlying implementation of bindat.el
doesn't matter much as long as bindat.el is used.

bug#34873: 27.0.50; Creating unibyte string in emacs modules

[Lars Ingebrigtsen]

Evgeny Zajcev <lg.zevlg@gmail.com> writes:

> There is no possibility to create unibyte strings from emacs modules
> in order to create some binary data representation

There was some discussion about what the meaning of "is" is that
followed, but the general idea seems sensible -- if modules are to be
able to pass binary data to Emacs efficiently, something like this is
needed, so I've now added this to Emacs 28 in the form of
make_unibyte_string.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

bug#34873: 27.0.50; Creating unibyte string in emacs modules

[Philipp Stephani]

Am Di., 13. Okt. 2020 um 06:53 Uhr schrieb Lars Ingebrigtsen <larsi@gnus.org>:
>
> Evgeny Zajcev <lg.zevlg@gmail.com> writes:
>
> > There is no possibility to create unibyte strings from emacs modules
> > in order to create some binary data representation
>
> There was some discussion about what the meaning of "is" is that
> followed, but the general idea seems sensible -- if modules are to be
> able to pass binary data to Emacs efficiently, something like this is
> needed, so I've now added this to Emacs 28 in the form of
> make_unibyte_string.
>


Thanks. However, you need to add it properly to maintain backward
compatibility; see the comments at the top of emacs-module.c.

bug#34873: 27.0.50; Creating unibyte string in emacs modules

[Lars Ingebrigtsen]

Philipp Stephani <p.stephani2@gmail.com> writes:

> Thanks. However, you need to add it properly to maintain backward
> compatibility; see the comments at the top of emacs-module.c.

OK; now moved to the right .h file.  (The comments referred to
emacs-env-27.h etc, which doesn't exist, so I assumed that it was
supposed to be module-env-27.h etc, and updated the comments.)

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no