Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!asuvax!ncar!gatech!prism!bb16
From: bb16@prism.gatech.EDU (Scott Bostater)
Newsgroups: comp.lang.pascal
Subject: Re: Sorting with 80x87
Message-ID: <28671@hydra.gatech.EDU>
Date: 10 May 91 15:20:46 GMT
References: <14826@ccncsu.ColoState.EDU>
Organization: Georgia Institute of Technology
Lines: 41

In article <14826@ccncsu.ColoState.EDU> mglacy@lamar.ColoState.EDU writes:
>
>I revised a program to take advantage of my 80287 co-processor.
>The program generates some 10,000 values of a random variable, then sorts
>them and outputs a frequency distribution for the variable. I find
>that, in the {$N+} mode, the program is only marginally faster in overall
>exec. time.  Everything except the sort seems to run MUCH faster, but
>the sort is now a real dog.  Sorting in {N+} mode is so slow that it negates 
>the time saved elsewhere in the program.
>

Are you still using REAL as your data type?   If so, change to either SINGLE
or DOUBLE.  What happens when you use REAL with {$N+} is as follows:

    1)  convert 1st 6 byte real to 8 byte double
    2)  load 8087 with double
    3)  convert 2nd 6 byte real to 8 byte double
    4)  load 8087 with double
    5)  have 8087 to compare function
    6)  *If* swap necessary
        6.1) Pop 8 byte double off 8087
        6.2) convert 8 byte double to 6 byte real
        6.3) Pop 8 byte double off 8087
        6.4) convert 8 byte double to 6 byte real

Needless to say there's a whole lot of converting going on and slowing you down

If you want a quick test just put the following at the begining of your program
(for purposes of readability and maintainabiliy I don't recommend this as a
permanent fix!)

type
  Real = Double;

This will change all your REAL's to DOUBLEs and you should notice a signifigant
speed up.
-- 
Scott Bostater      Georgia Tech Research Institute - Radar Systems Analysis
"My soul finds rest in God alone; my salvation comes from Him"  -Ps 62.1
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