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This noncompliant example first provides a constant value $BufferSize, set to 512. This constant can later be used to buffer data read in from a file. But then the code example defeats the purpose of defining $BufferSize as a constant by assuming its value in the subsequent expression:
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our $BufferSize = 512; # ... my $nblocks = 1 + (($nbytes - 1) >> 9); # because $BufferSize = 512 = 2^9 |
The programmer 's assumption underlying this code is might assume that "everyone knows that $BufferSize equals 512," and that right-shifting 9 bits is the same (for positive numbers) as dividing by 512. However, But if $BufferSize changes to 1024 on some systems, the subsequent expression must also be updated and can be overlooked easily. This makes modifications of constants difficult and error prone.
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