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Index > Main > Do you use BCDs?


Do you use BCDs?
Yes
44%
 44%  [ 4 ]
No
55%
 55%  [ 5 ]
What is a BCD?
0%
 0%  [ 0 ]
Total Votes : 9

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Ciper



Joined: 01 Jan 2013
Posts: 27
Ciper
Just curious...

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Ciper
Post 05 Jan 2013, 18:44
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HaHaAnonymous



Joined: 02 Dec 2012
Posts: 1180
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HaHaAnonymous
[ Post removed by author. ]


Last edited by HaHaAnonymous on 28 Feb 2015, 22:05; edited 1 time in total
Post 05 Jan 2013, 19:27
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baldr



Joined: 19 Mar 2008
Posts: 1651
baldr
Ciper,

Packed BCDs are quite useful when "USAGE IS DISPLAY" (in COBOL-speak). FASM internally uses unpacked BCZ (radix 36 numbers in their ASCII representation) for macro-local symbols' trailer.

These (almost forgotten) aaa/aad/aam/aas/daa/das instructions provide compact, while slow, methods to handle them well. OTOH, das was made popular by famous 5-byte sequence to convert nibble to its hex ASCII representation.

There is fbstp instruction for quick'n'dirty conversion to decimal representation, too.
Post 05 Jan 2013, 19:55
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Ciper



Joined: 01 Jan 2013
Posts: 27
Ciper
baldr,

Thank you very much for these clarifications; I believe people and (more seriously) compilers have discarded them too soon; most run-time libraries are certainly slower than these instructions.

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Ciper
Post 05 Jan 2013, 20:22
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baldr



Joined: 19 Mar 2008
Posts: 1651
baldr
Ciper,

Those aren't clarifications of any sort, I'd just pointed out that data usage dictates its representation. For computation-heavy usage, binary can be optimal; if you intend to convert them to textual (or any other) representation often, BCD (or any other easily converted to ASCII/other) representation can give your program sensible boost.

Those instructions are invalid in 64-bit code anyway (except fbstp, naturally Wink).
Post 05 Jan 2013, 20:37
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Ciper



Joined: 01 Jan 2013
Posts: 27
Ciper
baldr,

Retracting the 'clarifications' qualification...

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Ciper
Post 05 Jan 2013, 20:45
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cod3b453



Joined: 25 Aug 2004
Posts: 619
cod3b453
Never found a suitable time to use it until recently when comparing lots of ASCII decimal output, switching to hex diff saved some space and time.
Post 06 Jan 2013, 02:19
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baldr



Joined: 19 Mar 2008
Posts: 1651
baldr
cod3b453,

Comparison is probably not a good example of decimal-oriented data representation usage. Exach matching of arbitary strings can be processed (with good hash function) efficiently; most scripting languages use that technique to compare strings in almost O(1) time.
Post 06 Jan 2013, 04:47
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pool



Joined: 08 Jan 2007
Posts: 97
Location: Philippines
pool
..


Last edited by pool on 17 Mar 2013, 12:20; edited 1 time in total
Post 06 Jan 2013, 11:32
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cod3b453



Joined: 25 Aug 2004
Posts: 619
cod3b453
@baldr: My example wasn't about the comparison as much as the space usage - moving from (n+2) ASCII digits to n BCD digits simply meant 2-3 times less data to be stored/loaded from disk; hence faster to compare and less of a dent in my disk quota Razz
Post 06 Jan 2013, 12:22
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