crc and Ada

crc and Ada

[Bartłomiej Ś.]

Hello,
I'm starting in Ada, and I can't use same operators (like xor, and) in
my programs. I need to count crc. In Java I was writting:
#v+
...
crc=(crctable[((crc>>8)^bufor[start+i++]) & 0xFF]^(crc<<8))&0xFFFF;
...
#v-
What I should use instand of 'xor' and 'and' oparator (becouse in Ada
they are logical oparator, not binary). For example, I replace crc<<8 by
crc*256, and crc>>8 crc/256, but what about xor?

-- 
Best regards,         PGP: http://wilk.wpk.p.lodz.pl/swierczu/pgp
Bartek.               http://sknauk.wpk.p.lodz.pl  

Re: crc and Ada

[John R. Strohm]

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"Bart�omiej �." <swierczu@wpk.p.lodz.pl> wrote in message
news:slrnbcec3j.rh.swierczu@staticline881.toya.net.pl...
> Hello,
> I'm starting in Ada, and I can't use same operators (like xor, and) in
> my programs. I need to count crc. In Java I was writting:
> #v+
> ...
> crc=(crctable[((crc>>8)^bufor[start+i++]) & 0xFF]^(crc<<8))&0xFFFF;
> ...
> #v-
> What I should use instand of 'xor' and 'and' oparator (becouse in Ada
> they are logical oparator, not binary). For example, I replace crc<<8 by
> crc*256, and crc>>8 crc/256, but what about xor?

Check your compiler documentation.  They MAY export a machine intrinsics
package, which contains bitwise AND, OR, XOR, and such.

Check your compiler documentation.  Look for assembly language interfacing.
You certainly could write a little routine in assembly language that XOR'ed
two arguments and returned the result, and then hook it up to the Ada.

Also check your compiler documentation, for information about machine code
insertions.  CAUTION: Machine code insertions in Ada are NOT something a
novice should be tackling, but, occasionally, for political reasons, you can
get management approval for a machine code insertion where you couldn't get
approval for an assembly language subroutine.  (Been there, done that,
didn't WANT the T-shirt.)

Re: crc and Ada

[Martin Krischik]

Bart?omiej ?. wrote:

> Hello,

> What I should use instand of 'xor' and 'and' oparator (becouse in Ada
> they are logical oparator, not binary).

"xor" and "and" are not only boolean  operators. They can be used with
several datatypes. Also you can also define your own "xor" and "and"
operators.

> For example, I replace crc<<8 by
> crc*256, and crc>>8 crc/256, but what about xor?

I belive that in your case (crc calculation) a modular datatype (which have
predefined "xor", "and", "or" and "not" operators) might be alternative.
i.E.

type Unsigned_Byte is mod 2**8;
type Unsigned_Short is mod 2**16;
type Unsigned_Long is mod 2**32;

you might want to add a representation clause (if you don't trust the
compiler to make the right choice):

for Unsigned_Byte'Size use 8;
for Unsigned_Short'Size use 16;
for Unsigned_Long'Size use 32;

Remember that for a modular type wrap arount arithmetic (which for a CRC
calculation is probably what you want) is used. i.E.

Zero_Byte : Unsigned_Byte := 255 + 1;

Disclainer: This might not compile, it's just to show the general idea.

With Regarda

Martin

 
> --
> Best regards,         PGP: http://wilk.wpk.p.lodz.pl/swierczu/pgp
> Bartek.               http://sknauk.wpk.p.lodz.pl

-- 
--
mailto://krischik@users.sourceforge.net
http://www.ada.krischik.com

Re: crc and Ada

[Martin Dowie]

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"Bart�omiej �." <swierczu@wpk.p.lodz.pl> wrote in message
news:slrnbcec3j.rh.swierczu@staticline881.toya.net.pl...
> Hello,
> I'm starting in Ada, and I can't use same operators (like xor, and) in
> my programs. I need to count crc. In Java I was writting:
> #v+
> ...
> crc=(crctable[((crc>>8)^bufor[start+i++]) & 0xFF]^(crc<<8))&0xFFFF;
> ...
> #v-
> What I should use instand of 'xor' and 'and' oparator (becouse in Ada
> they are logical oparator, not binary). For example, I replace crc<<8 by
> crc*256, and crc>>8 crc/256, but what about xor?

You should check out 'modular types' and the standard package 'Interfaces'.

What compiler are you using? If the typical GNAT/AdaGIDE combo these
can be found under the Help->Language RM drop-down menu.

Also, check out www.adapower.com and the 'Learn Ada' option will take
you to link to a few free Ada95 books.

Good luck!

Re: crc and Ada

[tmoran]

> I'm starting in Ada, and I can't use same operators (like xor, and) in
Take another look at your Ada text.  There are indeed "and", "xor" etc
operators for modular (unsigned) types.

> crc=(crctable[((crc>>8)^bufor[start+i++]) & 0xFF]^(crc<<8))&0xFFFF;

type crc_type is mod 2**16;
crc : crc_type := initial value
type byte is mod 256;
crc_table : array(byte) of crc_type;

for i in start .. finish loop
  crc:=crc_table(byte(crc/256) xor bufor(i)) xor ((crc mod 256)*256);
end loop;

Re: crc and Ada

[Tarjei T. Jensen]

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"Bart�omiej �." wrote:
> crc=(crctable[((crc>>8)^bufor[start+i++]) & 0xFF]^(crc<<8))&0xFFFF;
> ...
> #v-
> What I should use instand of 'xor' and 'and' oparator (becouse in Ada
> they are logical oparator, not binary). For example, I replace crc<<8 by
> crc*256, and crc>>8 crc/256, but what about xor?

Read section 4.5.1 of the Ada 95 Reference Manual.

and, or and xor is defined for every bolean and modular type. In addtion
also single dimentioned arrays of boolean.

Also have a look Appendix B.2.


greetings,,

Re: crc and Ada

[Bartłomiej Ś.]

W artykule <M0Hxa.878367$3D1.501024@sccrnsc01> tmoran@acm.org napisaďż˝(a):
>> I'm starting in Ada, and I can't use same operators (like xor, and) in
> Take another look at your Ada text.  There are indeed "and", "xor" etc
> operators for modular (unsigned) types.
> 
>> crc=(crctable[((crc>>8)^bufor[start+i++]) & 0xFF]^(crc<<8))&0xFFFF;
> 
> type crc_type is mod 2**16;
> crc : crc_type := initial value
> type byte is mod 256;
> crc_table : array(byte) of crc_type;
> 
> for i in start .. finish loop
>   crc:=crc_table(byte(crc/256) xor bufor(i)) xor ((crc mod 256)*256);
> end loop;
I was made:
#v-

    function makeCrc (buffor : Stream_Element_Array; start : Stream_Element_Offset;
			len : Stream_Element_Offset) return Natural 
    is 

	package Output_Integers is new Ada.Text_IO.Modular_IO  (Unsigned_32);
	use Output_Integers;
	type CRC_Array is array (Unsigned_8) of Unsigned_32;

	crctable : CRC_Array := (	
	 16#0000#, 16#C0C1#, 16#C181#, 16#0140#, 16#C301#, 16#03C0#, 16#0280#, 16#C241#,	
	 16#C601#, 16#06C0#, 16#0780#, 16#C741#, 16#0500#, 16#C5C1#, 16#C481#, 16#0440#,
	 16#CC01#, 16#0CC0#, 16#0D80#, 16#CD41#, 16#0F00#, 16#CFC1#, 16#CE81#, 16#0E40#,
	 16#0A00#, 16#CAC1#, 16#CB81#, 16#0B40#, 16#C901#, 16#09C0#, 16#0880#, 16#C841#,
	 16#D801#, 16#18C0#, 16#1980#, 16#D941#, 16#1B00#, 16#DBC1#, 16#DA81#, 16#1A40#,
	 16#1E00#, 16#DEC1#, 16#DF81#, 16#1F40#, 16#DD01#, 16#1DC0#, 16#1C80#, 16#DC41#,
	 16#1400#, 16#D4C1#, 16#D581#, 16#1540#, 16#D701#, 16#17C0#, 16#1680#, 16#D641#,
	 16#D201#, 16#12C0#, 16#1380#, 16#D341#, 16#1100#, 16#D1C1#, 16#D081#, 16#1040#,
	 16#F001#, 16#30C0#, 16#3180#, 16#F141#, 16#3300#, 16#F3C1#, 16#F281#, 16#3240#,
	 16#3600#, 16#F6C1#, 16#F781#, 16#3740#, 16#F501#, 16#35C0#, 16#3480#, 16#F441#,
	 16#3C00#, 16#FCC1#, 16#FD81#, 16#3D40#, 16#FF01#, 16#3FC0#, 16#3E80#, 16#FE41#,
	 16#FA01#, 16#3AC0#, 16#3B80#, 16#FB41#, 16#3900#, 16#F9C1#, 16#F881#, 16#3840#,
	 16#2800#, 16#E8C1#, 16#E981#, 16#2940#, 16#EB01#, 16#2BC0#, 16#2A80#, 16#EA41#,
	 16#EE01#, 16#2EC0#, 16#2F80#, 16#EF41#, 16#2D00#, 16#EDC1#, 16#EC81#, 16#2C40#,	
	 16#E401#, 16#24C0#, 16#2580#, 16#E541#, 16#2700#, 16#E7C1#, 16#E681#, 16#2640#,
	 16#2200#, 16#E2C1#, 16#E381#, 16#2340#, 16#E101#, 16#21C0#, 16#2080#, 16#E041#,
	 16#A001#, 16#60C0#, 16#6180#, 16#A141#, 16#6300#, 16#A3C1#, 16#A281#, 16#6240#,
	 16#6600#, 16#A6C1#, 16#A781#, 16#6740#, 16#A501#, 16#65C0#, 16#6480#, 16#A441#,
	 16#6C00#, 16#ACC1#, 16#AD81#, 16#6D40#, 16#AF01#, 16#6FC0#, 16#6E80#, 16#AE41#,
	 16#AA01#, 16#6AC0#, 16#6B80#, 16#AB41#, 16#6900#, 16#A9C1#, 16#A881#, 16#6840#,
	 16#7800#, 16#B8C1#, 16#B981#, 16#7940#, 16#BB01#, 16#7BC0#, 16#7A80#, 16#BA41#,
	 16#BE01#, 16#7EC0#, 16#7F80#, 16#BF41#, 16#7D00#, 16#BDC1#, 16#BC81#, 16#7C40#,
	 16#B401#, 16#74C0#, 16#7580#, 16#B541#, 16#7700#, 16#B7C1#, 16#B681#, 16#7640#,
	 16#7200#, 16#B2C1#, 16#B381#, 16#7340#, 16#B101#, 16#71C0#, 16#7080#, 16#B041#,
	 16#5000#, 16#90C1#, 16#9181#, 16#5140#, 16#9301#, 16#53C0#, 16#5280#, 16#9241#,
	 16#9601#, 16#56C0#, 16#5780#, 16#9741#, 16#5500#, 16#95C1#, 16#9481#, 16#5440#,
	 16#9C01#, 16#5CC0#, 16#5D80#, 16#9D41#, 16#5F00#, 16#9FC1#, 16#9E81#, 16#5E40#,
	 16#5A00#, 16#9AC1#, 16#9B81#, 16#5B40#, 16#9901#, 16#59C0#, 16#5880#, 16#9841#,
	 16#8801#, 16#48C0#, 16#4980#, 16#8941#, 16#4B00#, 16#8BC1#, 16#8A81#, 16#4A40#,
	 16#4E00#, 16#8EC1#, 16#8F81#, 16#4F40#, 16#8D01#, 16#4DC0#, 16#4C80#, 16#8C41#,
	 16#4400#, 16#84C1#, 16#8581#, 16#4540#, 16#8701#, 16#47C0#, 16#4680#, 16#8641#,
	 16#8201#, 16#42C0#, 16#4380#, 16#8341#, 16#4100#, 16#81C1#, 16#8081#, 16#4040# );

	crc : Unsigned_32 := 0;
	i : Unsigned_8 := 0;

    begin
	while (i<Unsigned_8(len)) loop
	    crc := (crctable( Unsigned_8((crc/256) xor Unsigned_32 (buffor(start+Stream_Element_Offset(i)))) and 16#ff#) xor (crc*256)) and 16#ffff#;  
	    i := i + 1;
	end loop;
	return Natural(crc);
    end makeCrc;
#v-
Thank's for yours opinion and sugestion.
-- 
Pozdrowienia,         PGP: http://wilk.wpk.p.lodz.pl/swierczu/pgp
Bartek.               http://sknauk.wpk.p.lodz.pl  

Re: crc and Ada

[Ludovic Brenta]

Bart�omiej �. <swierczu@wpk.p.lodz.pl> writes:

> Hello,
> I'm starting in Ada, and I can't use same operators (like xor, and) in
> my programs. I need to count crc. In Java I was writting:

If your compiler is GNAT, there is the package System.CRC32.  Look at
the sources in lib/gcc-lib/.../.../adainclude/s-crc32.ad{b,s}.

There is also an older version of this file at:

http://korea.gnu.org/gcc/src/gcc-3.1/gcc/ada/s-crc32.adb
http://korea.gnu.org/gcc/src/gcc-3.1/gcc/ada/s-crc32.ads

FWIW, consider the following code:

type CRC32 is new Interfaces.Unsigned_32;
--  Used to represent CRC32 values, which are 32 bit bit-strings


procedure Update (C : in out CRC32; Value : Character) is
   V : constant CRC32 := CRC32 (Character'Pos (Value));
begin
   C := Shift_Right (C, 8) xor Table (V xor (C and 16#0000_00FF#));
end Update;

HTH

--
Ludovic Brenta.