[FFmpeg-devel] [PATCH] Make img_tags fall into .rodata

[Diego 'Flameeyes' Pettenò]

Michael Niedermayer <michaelni at gmx.at> writes:

> Why would we want it to be a power of 2?

Access to the N-th element of an array for the compiler is

*(&array + N*sizeof(array[0]))

when N is a power of 2, it would just be a shift to the right, rather
than a multiplication. On every architecture I know a bit of, shift to
right is faster than multiplication.

Of course if the compiler is good enough it would know it's iterating
sequentially and just use a temporary pointer and sum sizeof(array[0])
in it, but it's not bad to help out not-so-smart compilers, I didn't do
the math actually, but I'd say _if_ it wastes space on 32-bit
architectures, it's a very limited waste, which might actually help.

-- 
Diego "Flameeyes" Petten?
http://blog.flameeyes.eu/
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