Splitting the pointer arithmetic in GET_SYM() into a separate add and
sub instruction was an attempt to work around an error ("invalid operand
type") that occurred when assembling the file with NASM. However, this
created a link error on macOS ("ld: illegal text-relocation to
'_jconst_huff_encode_one_block' in
simd/CMakeFiles/simd.dir/i386/jchuff-sse2.asm.o from
'_jsimd_huff_encode_one_block_sse2' in
simd/CMakeFiles/simd.dir/i386/jchuff-sse2.asm.o for architecture i386")
and also changed the alignment of the code in ways that might have
affected the previous benchmark results (which took a great deal of time
to obtain.) Ultimately, the path of least resistance is just to
require NASM 2.13 or later.
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