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Groups > comp.os.linux.development.apps > #630

Re: memory use

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On Wed, 2 Feb 2011 20:50:45 +0000 (UTC), James Waldby wrote:
 > On Wed, 02 Feb 2011 18:02:31 +0000, Bob Tennent wrote:
 >
 >> A C program called musixflx is used as the second pass of a three-pass
 >> TeX-based system called musixtex.  The program was the first C program
 >> written by a Fortran programmer.  It has definitions as follows:
 >> 
 >>   # define MAX_BARS    2048  /* max number of bars */
 >> 
 >>   int zbar[MAX_BARS], lr_repeat[MAX_BARS], raggedline[MAX_BARS],
 >>       l_repeat[MAX_BARS], barno[MAX_BARS], ...
 >> 
 >>   double hardbarlength[MAX_BARS], softbarlength[MAX_BARS],
 >>          width_leftrightrepeat[MAX_BARS], width_leftrepeat[MAX_BARS],
 >>          ...
 >> Typically the number of bars in a piece is much smaller than MAX_BARS.
 >> 
 >> Would it be best to
 >> 
 >>  + leave the code alone and let the virtual-memory functions of the
 >>    operating system manage the memory
 >
 > Trying to reduce the 26KB used by those arrays probably is not 
 > worthwhile.
 >
 >>  + use "extensible" arrays (i.e., use realloc to copy small arrays to
 >>    larger ones when necessary)
 >
 > If scores are running up against the 2048-bar limit, just double or
 > quadruple MAX_BARS.[1]  The simplicity of fixed-size allocation is a
 > positive feature.  However, if these arrays were fixed at megabyte 
 > sizes and performance problems were occurring, allocating and 
 > reallocating might be worth considering, to reduce cache line refilling.
 >  
 >> And would there be any benefit to using a single array of structures
 >> instead of many parallel arrays?
 >
 > It looks like the code should have used structs when 
 > it was written, but unless for some reason you want to rewrite the whole
 > program it probably would not make sense to change from using parallel 
 > arrays to using structs.  

Thanks.

Bob T.

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Re: memory use James Waldby <not@valid.invalid> - 2011-02-02 20:50 +0000
  Re: memory use Bob Tennent <BobT@cs.queensu.ca> - 2011-02-02 21:16 +0000

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