operating with binary

[QQ]

Hi I have a unsigned char array, but I need to compress it in the bit
level.
for instance the array is 0x91,0x92,0x93. ...
I need to change it into a bit stream like 10010001 10010010 10010011
....
and operate this stream bit by bit and transform it into another bit
stream,
and convert that bit stream into an unsigned char array.
How can I do it?
Thanks a lot!

[Spiros Bousbouras]

QQ wrote:

Hi I have a unsigned char array, but I need to compress it in the bit
level.
for instance the array is 0x91,0x92,0x93. ...
I need to change it into a bit stream like 10010001 10010010 10010011
...
and operate this stream bit by bit and transform it into another bit
stream,
and convert that bit stream into an unsigned char array.
How can I do it?

What is the transformation you want to achieve between the
two bit streams ? Depending on that it may not be necessary
to turn it into a "bit stream" at all.

Having said that I'n not completely clear what you mean by
bit stream. Also why you are using the word compress.

[Nick Keighley]

QQ wrote:

like another poster I'm unclear what you want to do.

Hi I have a unsigned char array, but I need to compress it in the bit
level.
for instance the array is 0x91,0x92,0x93. ...
I need to change it into a bit stream like 10010001 10010010 10010011

you are aware that everything is already in binary? That 0x91 is just a

convenient notation for describing a binary number.

and operate this stream bit by bit and transform it into another bit
stream,

which you fail to specify...

and convert that bit stream into an unsigned char array.
How can I do it?

well if you want to take an array of unsigned char apply a
transformation
at the bit level to produce another array of unsigned char then you
probably
want to look at C's bit level operators. See &, |, ^, !, >and <<
(assuming
I didn't miss something).

If you want to print binary then you'll have to do something with
shifts and
masks to produce a sequence of '0' and '1' characters.

HTH

--
Nick Keighley

[Spiros Bousbouras]

Nick Keighley wrote:

well if you want to take an array of unsigned char apply a
transformation
at the bit level to produce another array of unsigned char then you
probably
want to look at C's bit level operators. See &, |, ^, !, >and <<
(assuming
I didn't miss something).

You probably meant ~ instead of !

[mospehraict]

for example, you can say

#define SIZE 8
#define BITS(n,x) ( ( (x) & (1<<(n)) ) >(n) )
#define GETBIT(n,x) (BITS((n)%SIZE, x[(n)/SIZE]))

and now you can say

unsigned int arr[3] = { 0x91, 0x92, 0x93 };

and say GETBIT(n,arr) to get/set n'th bit of arr.

QQ wrote:

Hi I have a unsigned char array, but I need to compress it in the bit
level.
for instance the array is 0x91,0x92,0x93. ...
I need to change it into a bit stream like 10010001 10010010 10010011
...
and operate this stream bit by bit and transform it into another bit
stream,
and convert that bit stream into an unsigned char array.
How can I do it?
Thanks a lot!

[mospehraict]

yup, the set will be a little different, though, but all the same old
way.

mospehra...@gma il.com wrote:

for example, you can say

#define SIZE 8
#define BITS(n,x) ( ( (x) & (1<<(n)) ) >(n) )
#define GETBIT(n,x) (BITS((n)%SIZE, x[(n)/SIZE]))

and now you can say

unsigned int arr[3] = { 0x91, 0x92, 0x93 };

and say GETBIT(n,arr) to get/set n'th bit of arr.

QQ wrote:

Hi I have a unsigned char array, but I need to compress it in the bit
level.
for instance the array is 0x91,0x92,0x93. ...
I need to change it into a bit stream like 10010001 10010010 10010011
...
and operate this stream bit by bit and transform it into another bit
stream,
and convert that bit stream into an unsigned char array.
How can I do it?
Thanks a lot!

[Frederick Gotham]

QQ posted:

Hi I have a unsigned char array, but I need to compress it in the bit
level.
for instance the array is 0x91,0x92,0x93. ...
I need to change it into a bit stream like 10010001 10010010 10010011
...
and operate this stream bit by bit and transform it into another bit
stream,
and convert that bit stream into an unsigned char array.
How can I do it?

This might get you started:

#include <stddef.h>
#include <assert.h>
#include <limits.h>
#include <stdio.h>

void PrintBits(void const *const mem,size_t amount_bytes,FI LE *const f)
{
int const assert_dummy =
(assert(!!mem), assert(!!amount _bytes),assert( !!f),0);

char static str[CHAR_BIT + 1] = {0};

char unsigned const *p = (char unsigned const*)mem;

do
{
unsigned const byte_val = *p++;
char *pos = str;

unsigned to_and_with = 1U << CHAR_BIT - 1;

do *pos++ = byte_val & to_and_with ? '1' : '0';
while(to_and_wi th >>= 1);

fprintf(f,str);
} while (--amount_bytes);
}

#define PrintObjBits(p, f) PrintBits((p),s izeof(*p),(f))

int main(void)
{
double long array[4] = {241.126, 632.225, 2662.2523, 23345.2352};

PrintObjBits(&a rray,stdout);

return 0;
}

--

Frederick Gotham

[CBFalconer]

mo*********@gma il.com wrote:

>
for example, you can say

#define SIZE 8
#define BITS(n,x) ( ( (x) & (1<<(n)) ) >(n) )
#define GETBIT(n,x) (BITS((n)%SIZE, x[(n)/SIZE]))

and now you can say

unsigned int arr[3] = { 0x91, 0x92, 0x93 };

and say GETBIT(n,arr) to get/set n'th bit of arr.

Don't top-post. It's rude, and we will not put up with it in this
newsgroup. See the links below.

--
Some informative links:
news:news.annou nce.newusers
http://www.geocities.com/nnqweb/
http://www.catb.org/~esr/faqs/smart-questions.html
http://www.caliburn.nl/topposting.html
http://www.netmeister.org/news/learn2quote.html

[Joe Wright]

QQ wrote:

Hi I have a unsigned char array, but I need to compress it in the bit
level.
for instance the array is 0x91,0x92,0x93. ...
I need to change it into a bit stream like 10010001 10010010 10010011
...
and operate this stream bit by bit and transform it into another bit
stream,
and convert that bit stream into an unsigned char array.
How can I do it?

First, you (or I) may misunderstand the problem. Let me change the
values of the array to printable ASCII for explanation purposes.

unsigned char array[] = {'a', 'b', 'c', '\0'};

In decimal this array is {97, 98, 99, 0}.
In hex, {0x01100001, 0x01100010, 0x01100011, 0x00000000}.

None of it is a 'stream' of anything (streams are to do with byte I/O
stuff, not with representations ). There is no 'bit stream'.

The finest granularity of memory objects in C is the byte, usually
unsigned char, and usually eight bits. A value of 0..255 decimal.

The *printf() utilities declared in stdio.h (provided in libc?) provide
means to 'print' (represent as text) the values you might present as
octal, decimal and hexadecimal. But not in Binary. We have to do it
ourselves. That's the bad news. The good news is that it's easy. Check
this out.

#define CHARBITS 8

typedef unsigned char uchar;

void bits(uchar b, int n) {
for (--n; n >= 0; --n)
putchar((b & 1 << n) ? '1' : '0');
putchar(' ');
}

void byte(uchar b) {
bits(b, CHARBITS);
}

If we call byte(x) we print 9 characters, eight of 0 or 1 and a trailing
space. Calling bits() prints the least significant n bits and a trailing
space. If you don't want to put all this to putchar(), direct it as you
will.

--
Joe Wright
"Everything should be made as simple as possible, but not simpler."
--- Albert Einstein ---

[Nick Keighley]

Joe Wright wrote:

QQ wrote:

In decimal this array is {97, 98, 99, 0}.
In hex, {0x01100001, 0x01100010, 0x01100011, 0x00000000}.

rather large hex numbers those...

--
Nick Keighley

Infinitely many bits doesn't give you "100% accuracy". You will
only be able to represent the algebraic numbers.

Sure, if you use one of those old-fashioned implementations that only
has aleph-null-bit floating-point. Any decent modern implementation
should provide at least aleph-one bits.
(Bill Pursell and Keith Thompson clc)