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global seat_id
section .rodata
align 16
xmm_shuf: db 8, 7, 6, 5, 4, 3, 2, 1, 0, 9, 10, 11, 12, 13, 14, 15
xmm_cmp: db 1, 'RBBBBBBB', 1, 1, 1, 1, 1, 1, 1
section .text
seat_id:
movq xmm0, qword [rdi] ; load first 8 bytes
pshufb xmm0, [rel xmm_shuf] ; reverse byte order and already shift left once
pcmpeqb xmm0, [rel xmm_cmp]
pmovmskb eax, xmm0 ; store mask in return value
xor ecx, ecx
cmp byte [rdi + 8], 'R'
sete cl
or eax, ecx
shl eax, 1
cmp byte [rdi + 9], 'R'
sete cl
or eax, ecx
ret
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