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devel / comp.os.cpm / Re: Direct directory search algorithm for CP/M3

SubjectAuthor
* Direct directory search algorithm for CP/M3rwd...@gmail.com
`* Re: Direct directory search algorithm for CP/M3John Elliott
 `- Re: Direct directory search algorithm for CP/M3rwd...@gmail.com

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Direct directory search algorithm for CP/M3

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Subject: Direct directory search algorithm for CP/M3
From: rwde...@gmail.com (rwd...@gmail.com)
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 by: rwd...@gmail.com - Sun, 13 Mar 2022 17:44 UTC

Does anyone know a method under CP/M 3 of determining the first directory entry for files in a directory, based on only searching the directory block, and not needing to cross refer to other directory entries?

Under CP/M 2 the first directory entry of a file was identified as having extent number zero. This does not apply under CP/M 3.

This method is used in the old Andrew Johnson Laird "FIND" program.

Currently to write a program that shows files across all drives and users I have to use search-first, search-next and set-user bdos calls which is a much slower method.

Richard

Re: Direct directory search algorithm for CP/M3

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Subject: Re: Direct directory search algorithm for CP/M3
From: joh...@seasip.info (John Elliott)
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 by: John Elliott - Mon, 14 Mar 2022 15:08 UTC

On Sunday, March 13, 2022 at 5:44:18 PM UTC, rwd...@gmail.com wrote:
> Does anyone know a method under CP/M 3 of determining the first directory entry for files in a directory, based on only searching the directory block, and not needing to cross refer to other directory entries?
>
> Under CP/M 2 the first directory entry of a file was identified as having extent number zero. This does not apply under CP/M 3.
>
> This method is used in the old Andrew Johnson Laird "FIND" program.
>
> Currently to write a program that shows files across all drives and users I have to use search-first, search-next and set-user bdos calls which is a much slower method.

Under both CP/M 2 and 3, you should AND the extent number with the inverse of the extent mask from the DPB. You should also check that directory byte S2 (offset 0Eh) is zero.

--
John Elliott

Re: Direct directory search algorithm for CP/M3

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Subject: Re: Direct directory search algorithm for CP/M3
From: rwde...@gmail.com (rwd...@gmail.com)
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 by: rwd...@gmail.com - Mon, 14 Mar 2022 17:22 UTC

On Monday, 14 March 2022 at 15:08:54 UTC, John Elliott wrote:
> On Sunday, March 13, 2022 at 5:44:18 PM UTC, rwd...@gmail.com wrote:
> > Does anyone know a method under CP/M 3 of determining the first directory entry for files in a directory, based on only searching the directory block, and not needing to cross refer to other directory entries?
> >
> > Under CP/M 2 the first directory entry of a file was identified as having extent number zero. This does not apply under CP/M 3.
> >
> > This method is used in the old Andrew Johnson Laird "FIND" program.
> >
> > Currently to write a program that shows files across all drives and users I have to use search-first, search-next and set-user bdos calls which is a much slower method.
> Under both CP/M 2 and 3, you should AND the extent number with the inverse of the extent mask from the DPB. You should also check that directory byte S2 (offset 0Eh) is zero.
>
> --
> John Elliott

Thank you John , I shall give that a go.
Richard

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