MESSAGE
| DATE | 2016-12-08 |
| FROM | ruben safir
|
| SUBJECT | Subject: [Learn] Fwd: png data format
|
From learn-bounces-at-nylxs.com Thu Dec 8 21:50:58 2016
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From: ruben safir
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Subject: png data format
Date: Tue, 6 Dec 2016 09:05:41 -0500
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Xref: panix comp.lang.c++:1125854
Hello
I'm having trouble with this imput of data from a PNG image. The specification says that "chunks" have a 4 byte field that is the length of the attached data segment. I tried to read the length in for a chunk that has a length of 13, which was confirmed in a hexdump
0000000 211 120 116 107 015 012 032 012 -->>000 000 000 015<<-- 111 110 104 122
0000010 000 000 041 215 000 000 007 165 010 006 000 000 001 206 055 074
0000020 336 000 000 000 004 147 101 115 101 000 000 261 217 013 374 141
I am storing the data in a uint32_t variable using the following code, but the value keeps showing up with a huge number 218103808 which happens to be the number that is evaluated by iostream for the value of the whole chunk
done reading header
Sizeof Chunk 4
Raw Chunk Number 0: 218103808
***LENGTH****
Length value => 218103808
Sizeof Byte 1
Character 0::
^-at-
Byte 0::
0
Character 1::
^-at-
Byte 1::
0
Character 2::
^-at-
Byte 2::
0
Character 3::
Byte 3::
13
As yet, when I break it down by single bytes, it returns 0 0 0 13, which is correct.
ddd seems to say the same thing, and I don't know why. When evaluated as 4 bytes,
you get this large number, but when you evaluate them seperately, each byte, it
comes out right.
The code snippet I'm using looks like this
in the .h file
#ifndef PNGPRJ
#define PNGPRJ
#include
namespace png_proj{
typedef uint32_t CHUNK;
In the .cpp file
void Image::read_chunk()
{
char * cur = get_index();
CHUNK * tmp = reinterpret_cast(cur);
std::cout << std::endl << "Sizeof Chunk " << sizeof(*tmp) << std::endl;
for(int j = 0; j<4; j++){
std::cout << "Raw Chunk Number " << j << ": " << *tmp << std::endl;
switch ( j ) {
case 0:
std::cout << "***LENGTH****" << std::endl;
set_length(static_cast(*tmp));
std::cout << "Length value => " << static_cast(*tmp) << std::endl;
break;
case 1:
std::cout << "***TYPE****" << std::endl;
set_type(static_cast(*tmp));
break;
case 2:
{
std::cout << "***DATA****" << std::endl;
unsigned long int l = static_cast(get_length());
std::cout << "buffer size should be " << get_length() << std::endl;
int8_t * buffer = new int8_t[l];
std::cout << "buffer element size is " << *buffer << std::endl;
std::cout << "buffer size is " << l << std::endl;
for(unsigned int k = 0; k < get_length(); k++){
buffer[k] = static_cast(tmp[k]);
std::cout << "data " << *buffer << std::endl;
}
set_data(buffer);
}
break;
case 3:
std::cout << "***CRC****" << std::endl;
set_crc(static_cast(*tmp));
break;
default:
std::cout << "***NOMANDSLAND****" << std::endl;
break;
} /* ----- end switch ----- */
char * tmp2 = reinterpret_cast(tmp); //reading each byte
std::cout << "Sizeof Byte " << sizeof(*tmp2) << std::endl;
//std::cout << "Mark ==>>" << __LINE__ << std::endl;
for(int i=0; i<4; i++){
std::cout << "Character " << i << "::" << std::endl << "\t" << *tmp2 << std::endl;
std::cout << "Byte " << i << "::" << std::endl << "\t" << static_cast(*tmp2) << std::endl;
tmp2++;
}
std::cout< std::cout< tmp++;
cur = ( reinterpret_cast(tmp) );
}
set_index(cur);
}
I dug through libpng since this seems to not being doing what I expected. They seem to set it up as 4 byte array
void /* PRIVATE */
png_push_read_chunk(png_structrp png_ptr, png_inforp info_ptr)
{
png_uint_32 chunk_name;
#ifdef PNG_HANDLE_AS_UNKNOWN_SUPPORTED
int keep; /* unknown handling method */
#endif
/* First we make sure we have enough data for the 4-byte chunk name
* and the 4-byte chunk length before proceeding with decoding the
* chunk data. To fully decode each of these chunks, we also make
* sure we have enough data in the buffer for the 4-byte CRC at the
* end of every chunk (except IDAT, which is handled separately).
*/
if ((png_ptr->mode & PNG_HAVE_CHUNK_HEADER) == 0)
{
png_byte chunk_length[4];
png_byte chunk_tag[4];
PNG_PUSH_SAVE_BUFFER_IF_LT(8)
png_push_fill_buffer(png_ptr, chunk_length, 4);
png_ptr->push_length = png_get_uint_31(png_ptr, chunk_length);
png_reset_crc(png_ptr);
png_crc_read(png_ptr, chunk_tag, 4);
png_ptr->chunk_name = PNG_CHUNK_FROM_STRING(chunk_tag);
png_check_chunk_name(png_ptr, png_ptr->chunk_name);
png_ptr->mode |= PNG_HAVE_CHUNK_HEADER;
}
I'm obviously not understanding something I'm evaluation here. So I'm wondering if anyone can shed light on this.
http://www.nylxs.com/docs/grad_school/parallel/src/png/png_proj.h
http://www.nylxs.com/docs/grad_school/parallel/src/png/png_proj.cpp
http://www.nylxs.com/docs/grad_school/parallel/src/png/main_png.cpp
http://www.nylxs.com/docs/grad_school/parallel/src/png/makefile
ruben
let.me.in
Ruben
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Xref: panix comp.lang.c++:1125858
ruben safir writes:
>Hello
>
>I'm having trouble with this imput of data from a PNG image. The specification says that "chunks" have a 4 byte field that is the length of the attached data segment. I tried to read the length in for a chunk that has a length of 13, which was confirmed in a hexdump
>
>0000000 211 120 116 107 015 012 032 012 -->>000 000 000 015<<-- 111 110 104 122
>0000010 000 000 041 215 000 000 007 165 010 006 000 000 001 206 055 074
>0000020 336 000 000 000 004 147 101 115 101 000 000 261 217 013 374 141
>
>I am storing the data in a uint32_t variable using the following code, but the value keeps showing up with a huge number 218103808 which happens to be the number that is evaluated by iostream for the value of the whole chunk
>
https://en.wikipedia.org/wiki/Endianness
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From: ruben safir
Newsgroups: comp.lang.c++
Subject: Re: png data format
Date: Tue, 6 Dec 2016 13:42:12 -0500
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Xref: panix comp.lang.c++:1125865
On 12/06/2016 10:10 AM, Scott Lurndal wrote:
> ruben safir writes:
>> Hello
>>
>> I'm having trouble with this imput of data from a PNG image. The specification says that "chunks" have a 4 byte field that is the length of the attached data segment. I tried to read the length in for a chunk that has a length of 13, which was confirmed in a hexdump
>>
>> 0000000 211 120 116 107 015 012 032 012 -->>000 000 000 015<<-- 111 110 104 122
>> 0000010 000 000 041 215 000 000 007 165 010 006 000 000 001 206 055 074
>> 0000020 336 000 000 000 004 147 101 115 101 000 000 261 217 013 374 141
>>
>> I am storing the data in a uint32_t variable using the following code, but the value keeps showing up with a huge number 218103808 which happens to be the number that is evaluated by iostream for the value of the whole chunk
>>
>
> https://en.wikipedia.org/wiki/Endianness
>
that doesn't help
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Xref: panix comp.lang.c++:1125868
ruben safir writes:
>On 12/06/2016 10:10 AM, Scott Lurndal wrote:
>> ruben safir writes:
>>> Hello
>>>
>>> I'm having trouble with this imput of data from a PNG image. The specification says that "chunks" have a 4 byte field that is the length of the attached data segment. I tried to read the length in for a chunk that has a length of 13, which was confirmed in a hexdump
>>>
>>> 0000000 211 120 116 107 015 012 032 012 -->>000 000 000 015<<-- 111 110 104 122
>>> 0000010 000 000 041 215 000 000 007 165 010 006 000 000 001 206 055 074
>>> 0000020 336 000 000 000 004 147 101 115 101 000 000 261 217 013 374 141
>>>
>>> I am storing the data in a uint32_t variable using the following code, but the value keeps showing up with a huge number 218103808 which happens to be the number that is evaluated by iostream for the value of the whole chunk
>>>
>>
>> https://en.wikipedia.org/wiki/Endianness
>>
>
>
>that doesn't help
And nobody here is obligated to help you - you should learn to
help yourself, and the link referenced above should be your starting
point.
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From: ruben safir
Newsgroups: comp.lang.c++
Subject: Re: png data format
Date: Tue, 6 Dec 2016 14:33:37 -0500
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Xref: panix comp.lang.c++:1125869
On 12/06/2016 02:05 PM, Scott Lurndal wrote:
> ruben safir writes:
>> On 12/06/2016 10:10 AM, Scott Lurndal wrote:
>>> ruben safir writes:
>>>> Hello
>>>>
>>>> I'm having trouble with this imput of data from a PNG image. The specification says that "chunks" have a 4 byte field that is the length of the attached data segment. I tried to read the length in for a chunk that has a length of 13, which was confirmed in a hexdump
>>>>
>>>> 0000000 211 120 116 107 015 012 032 012 -->>000 000 000 015<<-- 111 110 104 122
>>>> 0000010 000 000 041 215 000 000 007 165 010 006 000 000 001 206 055 074
>>>> 0000020 336 000 000 000 004 147 101 115 101 000 000 261 217 013 374 141
>>>>
>>>> I am storing the data in a uint32_t variable using the following code, but the value keeps showing up with a huge number 218103808 which happens to be the number that is evaluated by iostream for the value of the whole chunk
>>>>
>>>
>>> https://en.wikipedia.org/wiki/Endianness
>>>
>>
>>
>> that doesn't help
>
> And nobody here is obligated to help you - you should learn to
> help yourself, and the link referenced above should be your starting
> point.
>
no it is not really. Like most wikipedia articles it is written poorly
and leaves of coherent details. Your under no obligation to post, if
you don't want to contribute. Being an ass isn't helpful though and
treating me like I'm stupid makes me resentful
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Subject: Re: png data format
Newsgroups: comp.lang.c++
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From: Luuk
Date: Tue, 6 Dec 2016 20:51:07 +0100
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Xref: panix comp.lang.c++:1125870
On 06-12-16 20:33, ruben safir wrote:
> On 12/06/2016 02:05 PM, Scott Lurndal wrote:
>> ruben safir writes:
>>> On 12/06/2016 10:10 AM, Scott Lurndal wrote:
>>>> ruben safir writes:
>>>>> Hello
>>>>>
>>>>> I'm having trouble with this imput of data from a PNG image. The specification says that "chunks" have a 4 byte field that is the length of the attached data segment. I tried to read the length in for a chunk that has a length of 13, which was confirmed in a hexdump
>>>>>
>>>>> 0000000 211 120 116 107 015 012 032 012 -->>000 000 000 015<<-- 111 110 104 122
>>>>> 0000010 000 000 041 215 000 000 007 165 010 006 000 000 001 206 055 074
>>>>> 0000020 336 000 000 000 004 147 101 115 101 000 000 261 217 013 374 141
>>>>>
>>>>> I am storing the data in a uint32_t variable using the following code, but the value keeps showing up with a huge number 218103808 which happens to be the number that is evaluated by iostream for the value of the whole chunk
>>>>>
>>>>
>>>> https://en.wikipedia.org/wiki/Endianness
>>>>
>>>
>>>
>>> that doesn't help
>>
>> And nobody here is obligated to help you - you should learn to
>> help yourself, and the link referenced above should be your starting
>> point.
>>
>
> no it is not really. Like most wikipedia articles it is written poorly
> and leaves of coherent details. Your under no obligation to post, if
> you don't want to contribute. Being an ass isn't helpful though and
> treating me like I'm stupid makes me resentful
>
Basically the wikipeadia page explains what is stated in the docs here:
http://www.libpng.org/pub/png/spec/1.2/PNG-DataRep.html#DR.Integers-and-byte-order
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From: David Brown
Newsgroups: comp.lang.c++
Subject: Re: png data format
Date: Tue, 6 Dec 2016 21:41:26 +0100
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Xref: panix comp.lang.c++:1125871
On 06/12/16 20:33, ruben safir wrote:
> On 12/06/2016 02:05 PM, Scott Lurndal wrote:
>> ruben safir writes:
>>> On 12/06/2016 10:10 AM, Scott Lurndal wrote:
>>>> ruben safir writes:
>>>>> Hello
>>>>>
>>>>> I'm having trouble with this imput of data from a PNG image. The specification says that "chunks" have a 4 byte field that is the length of the attached data segment. I tried to read the length in for a chunk that has a length of 13, which was confirmed in a hexdump
>>>>>
>>>>> 0000000 211 120 116 107 015 012 032 012 -->>000 000 000 015<<-- 111 110 104 122
>>>>> 0000010 000 000 041 215 000 000 007 165 010 006 000 000 001 206 055 074
>>>>> 0000020 336 000 000 000 004 147 101 115 101 000 000 261 217 013 374 141
>>>>>
>>>>> I am storing the data in a uint32_t variable using the following code, but the value keeps showing up with a huge number 218103808 which happens to be the number that is evaluated by iostream for the value of the whole chunk
>>>>>
>>>>
>>>> https://en.wikipedia.org/wiki/Endianness
>>>>
>>>
>>>
>>> that doesn't help
>>
>> And nobody here is obligated to help you - you should learn to
>> help yourself, and the link referenced above should be your starting
>> point.
>>
>
> no it is not really. Like most wikipedia articles it is written poorly
> and leaves of coherent details. Your under no obligation to post, if
> you don't want to contribute. Being an ass isn't helpful though and
> treating me like I'm stupid makes me resentful
>
The Wikipedia article there is reasonably written, and full of useful
information. But you may not have made the connection as to why it is
relevant to your problem.
Numbers bigger than single bytes in computing can be stored in two basic
formats - big endian with the most significant byte first, and little
endian with the least significant byte first. Some processors use one
format, other processors use the other. Some file formats and protocols
use one format, others use the other. If the processor and the file
format do not match, then you need to convert when reading or writing
the format.
x86 uses little endian format, so 13 is stored as 0b 00 00 00 as a
32-bit integer. PNG, like many network-related formats, uses big
endian. So it stores 32-bit 13 as 00 00 00 0b. (Incidentally, use hex
for this sort of thing - octal had no place in computing outside of
"chmod" since the 1970's.)
Assuming you are trying to learn and understand this, rather than
copy-and-paste working code, then this should be enough to get you going.
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Subject: Re: png data format
Date: Tue, 6 Dec 2016 17:12:21 -0500
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Xref: panix comp.lang.c++:1125872
On 12/06/2016 03:41 PM, David Brown wrote:
> The Wikipedia article there is reasonably written
no it isn't. But I'll show you a means of properly answering a question
like this
http://www.nylxs.com/messages.html?id=543540&archive_learn=2016-12-01
All it takes is a basic assumption that your not talking to an idiot.
Specifically that wikipedea article, and really they all suck, don't
explain how the intel hardware is set up and who to evaluate the and
learn the problem solving mechanism, so that one can learn to evaluate
these kinds of problems in the future.
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From: David Brown
Newsgroups: comp.lang.c++
Subject: Re: png data format
Date: Wed, 7 Dec 2016 23:59:24 +0100
Organization: A noiseless patient Spider
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Xref: panix comp.lang.c++:1125901
On 06/12/16 23:12, ruben safir wrote:
> On 12/06/2016 03:41 PM, David Brown wrote:
>> The Wikipedia article there is reasonably written
>
> no it isn't. But I'll show you a means of properly answering a question
> like this
>
> http://www.nylxs.com/messages.html?id=543540&archive_learn=2016-12-01
>
>
> All it takes is a basic assumption that your not talking to an idiot.
I don't assume you are an idiot (though your posting style does not do
wonders for the impression you give). I assume you want to learn and
understand what you are doing - otherwise you would simply use a
pre-written png library.
>
> Specifically that wikipedea article, and really they all suck, don't
> explain how the intel hardware is set up and who to evaluate the and
> learn the problem solving mechanism, so that one can learn to evaluate
> these kinds of problems in the future.
>
The Wikipedia article is about Endianness, not Intel hardware, or png
file formats. It has a clear enough explanation about what endianness
means, a bit of history and examples, some reasons for choosing one
endianness type over another, and example code of a way to swap
endianness. What more do you want? A special section entitled "why
your png decoder is not working on an Intel cpu"?
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From: ruben safir
Newsgroups: comp.lang.c++
Subject: Re: png data format
Date: Wed, 7 Dec 2016 23:23:58 -0500
Organization: PANIX Public Access Internet and UNIX, NYC
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Xref: panix comp.lang.c++:1125905
On 12/07/2016 05:59 PM, David Brown wrote:
> would simply use a pre-written png library.
thats 100% true. But along with that means I would do a huge research
first through the dozen C++ and PNG texts I have and a duckduckgo
search, BEFORE posting.
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From: ruben safir
Newsgroups: comp.lang.c++
Subject: Re: png data format
Date: Wed, 7 Dec 2016 23:24:35 -0500
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Xref: panix comp.lang.c++:1125906
On 12/07/2016 05:59 PM, David Brown wrote:
> clear enough explanation about what endianness means,
no, it doesn't. Maybe you can reedit it.
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From: Robert Wessel
Newsgroups: comp.lang.c++
Subject: Re: png data format
Message-ID: <81th4ctdjpud70gbud62m567f3f1djvfi1-at-4ax.com>
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Xref: panix comp.lang.c++:1125907
On Wed, 7 Dec 2016 23:24:35 -0500, ruben safir
wrote:
>On 12/07/2016 05:59 PM, David Brown wrote:
>> clear enough explanation about what endianness means,
>
>
>no, it doesn't. Maybe you can reedit it.
As a regular WP editor (although I don't believe I've ever edited that
particular article), I may be biased, but it looks like a pretty good
article to me. Clear, concise, complete and well referenced - you
really can't ask for much more (the article's "B" class rating
suggests that I'm not the only one with that opinion). The basic
concept is explained in the first introductory paragraph, and then
nicely illustrated in two illustrations in the immediately following
"Illustration" section.
OTOH, I do know what endianness is, which may be leading me to making
incorrect assumptions about the context in which someone without that
knowledge would be reading the article, leading to some significant
omitted information. If you have some constructive criticism
regarding how the article failed you, I can certainly take a look at
improving it.
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NNTP-Posting-Date: Thu, 08 Dec 2016 01:26:02 -0600
From: Gareth Owen
Newsgroups: comp.lang.c++
Subject: Re: png data format
References:
Date: Thu, 08 Dec 2016 07:26:02 +0000
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Xref: panix comp.lang.c++:1125909
ruben safir writes:
> On 12/07/2016 05:59 PM, David Brown wrote:
>> clear enough explanation about what endianness means,
>
>
> no, it doesn't. Maybe you can reedit it.
Maybe the problem is not with the article? Try this one.
https://simple.wikipedia.org/wiki/Endianness
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Date: Thu, 08 Dec 2016 10:08:37 +0200
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Xref: panix comp.lang.c++:1125910
On 8.12.2016 9:26, Gareth Owen wrote:
> ruben safir writes:
>
>> On 12/07/2016 05:59 PM, David Brown wrote:
>>> clear enough explanation about what endianness means,
>>
>>
>> no, it doesn't. Maybe you can reedit it.
>
> Maybe the problem is not with the article? Try this one.
> https://simple.wikipedia.org/wiki/Endianness
"For each hard question there is a simple, easily understandable wrong
answer" - except that this article is IMO wrong, but still not easily
understandable. What is "hexadecimal data"? Is AB12 really encoded in 4
bits?
Why they want to couple endianness with some binary data representation?
In a "simple pedia" like that I would stick to our common decimal
representation and just say that the number ten is written by two
digits: 0 and 1, which can be ordered either as 01 or 10. I also would
talk something about Gulliver and about the egg-eater wars and who has won.
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From: "Alf P. Steinbach"
Newsgroups: comp.lang.c++
Subject: Re: png data format
Date: Thu, 8 Dec 2016 09:32:13 +0100
Organization: A noiseless patient Spider
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Xref: panix comp.lang.c++:1125911
On 08.12.2016 09:08, Paavo Helde wrote:
> On 8.12.2016 9:26, Gareth Owen wrote:
>> ruben safir writes:
>>
>>> On 12/07/2016 05:59 PM, David Brown wrote:
>>>> clear enough explanation about what endianness means,
>>>
>>>
>>> no, it doesn't. Maybe you can reedit it.
>>
>> Maybe the problem is not with the article? Try this one.
>> https://simple.wikipedia.org/wiki/Endianness
>
> "For each hard question there is a simple, easily understandable wrong
> answer" - except that this article is IMO wrong, but still not easily
> understandable. What is "hexadecimal data"? Is AB12 really encoded in 4
> bits?
>
> Why they want to couple endianness with some binary data representation?
> In a "simple pedia" like that I would stick to our common decimal
> representation and just say that the number ten is written by two
> digits: 0 and 1, which can be ordered either as 01 or 10. I also would
> talk something about Gulliver and about the egg-eater wars and who has won.
Not everybody knows that Jonathan Swift wrote the original
recursion-poem, that Augustus De Morgan based his more well-known
variant on. So, first of all, Jonathan Swift ? Augustus De Morgan.
Then there's the connection George Boole ? (friendly
article/book-publishing competitor with) Augustus DeMorgan ? (private
math tutor to) Lady Augusta Ada ? (coder and sort of secretary for)
Charles Babbage ? first general programmable computer.
I remember getting almost angry when some American professor wrote an
article about the history of computers in Scientific American, and
managed to omit all that crucial English history. He started with
something about Napoleon, skipped the German/English part entirely, and
ended with the US developments after WWII. I think he even managed to
omit that John von Neumann was Hungarian, like, he was an American.
Not sure how much of this to include in an article about endianness, though.
But it would be nice with a discussion of the endianness of Babbage's
analytical engine.
Cheers!,
- Alf
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From: legalize+jeeves-at-mail.xmission.com (Richard)
Newsgroups: comp.lang.c++
Subject: Re: png data format
Date: Thu, 8 Dec 2016 18:02:12 +0000 (UTC)
Organization: multi-cellular, biological
Sender: legalize+jeeves-at-mail.xmission.com
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Xref: panix comp.lang.c++:1125921
[Please do not mail me a copy of your followup]
Paavo Helde spake the secret code
thusly:
>"For each hard question there is a simple, easily understandable wrong
>answer" - except that this article is IMO wrong, but still not easily
>understandable. What is "hexadecimal data"? Is AB12 really encoded in 4
>bits?
What is hexadecimal data? Seriously? Are you unable to google or
use WP's search box?
Never mind that "hexadecimal" is linked right in the article.
Nowhere in that article could I find the data 0xAB12.
>Why they want to couple endianness with some binary data representation?
Because the discussion of endianness is meaningless without
discussing how things are stored as binary values in memory or on a
communication stream.
If you don't care how things are stored or transmitted in some binary
form, then you don't care about endianness.
--
"The Direct3D Graphics Pipeline" free book
The Terminals Wiki
The Computer Graphics Museum
Legalize Adulthood! (my blog)
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Xref: panix comp.lang.c++:1125924
On 8.12.2016 20:02, Richard wrote:
> [Please do not mail me a copy of your followup]
>
> Paavo Helde spake the secret code
> thusly:
>
>> "For each hard question there is a simple, easily understandable wrong
>> answer" - except that this article is IMO wrong, but still not easily
>> understandable. What is "hexadecimal data"? Is AB12 really encoded in 4
>> bits?
>
> What is hexadecimal data? Seriously? Are you unable to google or
> use WP's search box?
Tell me, what is "hexadecimal data"? I can understand what is
"hexadecimal representation of data", but "hexadecimal data"? If a
weather station reports temperature 25?C, is this "hexadecimal data" or not?
>
> Nowhere in that article could I find the data 0xAB12.
Are you sure you looked at the same article?
https://simple.wikipedia.org/wiki/Endianness
It appears user Dearingj has changed 'bits' to 'pieces' today, so maybe
all my nitpicking is not in vain ;-)
Cheers
Paavo
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NNTP-Posting-Date: Thu, 08 Dec 2016 14:00:41 -0600
From: Gareth Owen
Newsgroups: comp.lang.c++
Subject: Re: png data format
References:
<87eg1ivq45.fsf-at-gmail.com>
Date: Thu, 08 Dec 2016 20:00:40 +0000
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Xref: panix comp.lang.c++:1125925
Paavo Helde writes:
> On 8.12.2016 20:02, Richard wrote:
>> [Please do not mail me a copy of your followup]
>>
>> Paavo Helde spake the secret code
>> thusly:
>>
>>> "For each hard question there is a simple, easily understandable wrong
>>> answer" - except that this article is IMO wrong, but still not easily
>>> understandable. What is "hexadecimal data"? Is AB12 really encoded in 4
>>> bits?
>>
>> What is hexadecimal data? Seriously? Are you unable to google or
>> use WP's search box?
>
> Tell me, what is "hexadecimal data"? I can understand what is
> "hexadecimal representation of data", but "hexadecimal data"? If a
> weather station reports temperature 25°C, is this "hexadecimal data"
> or not?
You are technically correct, the best sort of correct.
However, you *don't* really not understand what "hexadecimal data"
means, you're just being an annoying pedant.
Pedantry and simplicity are often at odds. Can you guess which way
Simple Wikipedia tends to lean?
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From: Christian Gollwitzer
Newsgroups: comp.lang.c++
Subject: Re: png data format
Date: Thu, 8 Dec 2016 21:36:57 +0100
Organization: A noiseless patient Spider
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Xref: panix comp.lang.c++:1125926
Am 08.12.2016 um 21:00 schrieb Gareth Owen:
> Pedantry and simplicity are often at odds. Can you guess which way
> Simple Wikipedia tends to lean?
Maybe, but that particular article is both not simple and incorrect.
A) Not simple: The second sentence has nested parataxes (indicated by
brackets)
"In computer coding, certain numbers, [usually two bytes long (1 byte
= 8 bits) [ that are called "words",] ] can be written or input in two ways"
B) Incorrect: It says that the number 0x12AB in big endian is 12|AB,
because "the bigger number comes at the end", explaining the hexadecimal
digits 0..9A..F. So it is big endian, because AB > 12 ? I can't seem to
understand the sentence in the correct way, it is definitely incorrect
Christian
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Date: Thu, 08 Dec 2016 22:40:30 +0200
From: Paavo Helde
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Subject: Re: png data format
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Xref: panix comp.lang.c++:1125927
On 8.12.2016 22:00, Gareth Owen wrote:
> Paavo Helde writes:
>
>> On 8.12.2016 20:02, Richard wrote:
>>> [Please do not mail me a copy of your followup]
>>>
>>> Paavo Helde spake the secret code
>>> thusly:
>>>
>>>> "For each hard question there is a simple, easily understandable wrong
>>>> answer" - except that this article is IMO wrong, but still not easily
>>>> understandable. What is "hexadecimal data"? Is AB12 really encoded in 4
>>>> bits?
>>>
>>> What is hexadecimal data? Seriously? Are you unable to google or
>>> use WP's search box?
>>
>> Tell me, what is "hexadecimal data"? I can understand what is
>> "hexadecimal representation of data", but "hexadecimal data"? If a
>> weather station reports temperature 25°C, is this "hexadecimal data"
>> or not?
>
> You are technically correct, the best sort of correct.
>
> However, you *don't* really not understand what "hexadecimal data"
> means, you're just being an annoying pedant.
>
> Pedantry and simplicity are often at odds. Can you guess which way
> Simple Wikipedia tends to lean?
That's what I said, "simple and wrong". The notion of 'endianness' and
the notion of 'data' have nothing whatsoever to do with 'hexadecimal',
so why the Wikipedia article starts with "Endianness refers to how
hexadecimal data is ordered ..."?
I can understand that people like simple and wrong explanations. I just
don't approve it. But in this case, I feel that 'hexadecimal' is
actually complicating the things, instead of making them simpler. This
article should not contain 'hexadecimal' at all.
Cheers
Paavo
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