The apple assembler for arm can handle the gnu binutils style
macros just fine these days, so there is no need to duplicate all
of these macros in two syntaxes, when the new one works fine in all cases.
We already require a new enough assembler to support the gnu binutils
style features since we use the .rept directive in a few places.
Previously the assembly sources had mixed indentation consisting
of both spaces and tabs, making it quite hard to read unless
the right tab size was used in the editor.
Tabs have been interpreted as 4 spaces in most cases, matching
the surrounding code.
According to the calling convention, the registers q4-q7 should be
preserved by functions. The caller (generated by the compiler) could
be using those registers anywhere for any intermediate data.
Functions that use more than 12 of the qX registers must push
the clobbered registers on the stack in order to be able to restore them
afterwards.
In functions that don't use all 16 registers, but clobber some of
the callee saved registers q4-q7, one or more of them are remapped
to reduce the number of registers that have to be saved/restored.
This incurs a very small (around 0.5%) slowdown in the decoder and
encoder.
According to the calling convention, the registers q4-q7 should be
preserved by functions. The caller (generated by the compiler) could
be using those registers anywhere for any intermediate data.
Functions that use 12 or less of the qX registers can avoid
violating the calling convention by simply using other registers instead
of the callee saved registers q4-q7.
This change only remaps the registers used within functions - therefore
this does not affect performance at all. E.g. in functions using
registers q0-q7, we now use q0-q3 and q8-q11 instead.
There's a different version of the same function in the encoder,
but they're not identical - the encoder version has got stricter
alignment requirements.
If someone can confirm that it is ok to use the function from the
encoder, pixel_sad_neon.S in processing could be deleted, and the
encoder version moved to codec/common instead.
