Q59255: C 5.10 Has a Default Threshold of 32,767 Bytes

Article: Q59255
Product(s): See article
Version(s): 5.10 6.00 | 5.10 6.00
Operating System(s): MS-DOS | OS/2
Keyword(s): ENDUSER | | mspl13_c
Last Modified: 15-MAY-1990

Question:

I am developing a real-time, 3-D graphics application in large model
that uses a rather large static array of structures. I expand the size
of my array by one element, and my program runs significantly slower.
I restore the size of my array to its original value, and the program
runs at normal speed. What is the cause of this problem?

Response:

The C version 5.10 compiler has a default data threshold value of
32,767 bytes. The size of your static array is probably close to that
of the default data threshold and when you add another element, it
puts you over the limit. In that case, your data is moved to a far
data segment, thus causing the speed hit on your program.

To work around this problem, you could set /Gt to a value greater than
the size of your static array, or you could explicitly declare the
array as being near.

For more information on the /Gt switch, refer to the "Microsoft C
Optimizing Compiler User's Guide."

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