RE: Making the present code run faster

["Albertson, Chris" <CAlbertson@primeadvantage.com>]

Don't try to do FITS format file on your own.  There's no
point.  Except as an excercise if you have time to kill.  The
CFITSIO library is the only way to go.  It handles
the blocking for you.    The feature list is longer then your
arm and it runs on just about any kind of computer.  There is
no way you could duplicate CFITSIO in only a few months.
The library is in such common use that you could even say
the it _defines_ the FITS file format.

CFITSIO goes on step farther the what you did. It maintains a
block cache in RAM.  It writes out the bloks using random I/O
as required.  If you have enough RAM nothing really is commited
to disk until the file is closed.  The cache algorithum was
been tweeked and re-tweeked for years now an is about as good
as it is going to get.  As I said befor, I can write FITS
at the hardware "media speed" using only a P200.


> -----Original Message-----
> From: Andrew Bennett [mailto:andrew.bennett@ns.sympatico.ca]
> Sent: Tuesday, January 30, 2001 12:48 PM
> To: Tom Droege; tass@listserv.wwa.com
> Subject: Re: Making the present code run faster
> 
> 
> On Mon, 29 Jan 2001 13:34:04 -0600, Tom Droege 
> <tdroege@veriomail.com> or somebody wrote:
> 
> >   Then it is not a question of CPU speed, but rather disk
> >speed or some interaction between the BASIC code and disk
> >writing.
> 
> The biggest single factor in speeding up my Pascal
> code was to quit trying to write in 2880 Byte chunks
> (for FITS) and instead to block the data up in 2^n
> segments. The odd sizes really screwed up the system
> with or without SMARTDRV. With SMARTDRV, one could
> use relatively short 2^n blocks without penalty. I used
> 16384 Bytes.
> 
> I know nothing about Windows caching - I suspect it
> will also be badly affected by non-2^n blocks.
> 
> My Pascal code looked like this:
>   L := NAxis1*NAxis2 ; { Size in 16-bit words }
>   N := LBufW ; { 8192 = 16384/2 }
>   I := 0 ;
>   Repeat
>     B1 := InPortB(PortNo) ;
>     B2 := InPortB(PortNo) ;
>     BufA[I] := 256*Word(B1) + B2 ;
>     B1 := InPortB(PortNo) ;
>     B2 := InPortB(PortNo) ;
>     BufB[I] := 256*Word(B1) + B2 ;
>     Inc(I) ;
>     If (I >= N) Then Begin
>       BlockWrite(FileA, BufA, N) ;
>       BlockWrite(FileB, BufB, N) ;
>       Dec(L, N) ;
>       N := L ; If (N > LBufW) Then N := LBufW ;
>       I := 0 ;
>     End ;
>   Until (L <= 0) ;
> 
> I'm sorry, but I don't know enough BASIC to translate
> this back. Note that the last disk writes are a
> different size from the others so I could not
> use File Of BufType; I was effectively using
> File Of Word; N is the number of words to be
> written (record size of 2 Bytes).
> 
> Andrew Bennett, Avondale Vineyard
>