mov %rdi,%rax
    mov $0x5555555555555555,%rsi
    and %rax,%rsi
    sal $1,%rsi
    mov $0xAAAAAAAAAAAAAAAA,%rdx
    and %rax,%rdx
    sar $1,%rdx
    or %rdx,%rsi
    mov %rsi,%rax
    mov $0x3333333333333333,%rsi
    and %rax,%rsi
    sal $2,%rsi
    mov $0xCCCCCCCCCCCCCCCC,%rdx
    and %rax,%rdx
    sar $2,%rdx
    or %rdx,%rsi
    mov %rsi,%rax
    mov $0x0F0F0F0F0F0F0F0F,%rsi
    and %rax,%rsi
    sal $4,%rsi
    mov $0xF0F0F0F0F0F0F0F0,%rdx
    and %rax,%rdx
    sar $4,%rdx
    or %rdx,%rsi
    mov %rsi,%rax
    mov $0x00FF00FF00FF00FF,%rsi
    and %rax,%rsi
    sal $8,%rsi
    mov $0xFF00FF00FF00FF00,%rdx
    and %rax,%rdx
    sar $8,%rdx
    or %rdx,%rsi
    mov %rsi,%rax
    mov $0x0000FFFF0000FFFF,%rsi
    and %rax,%rsi
    sal $16,%rsi
    mov $0xFFFF0000FFFF0000,%rdx
    and %rax,%rdx
    sar $16,%rdx
    or %rdx,%rsi
    mov %rsi,%rax
    mov $0x00000000FFFFFFFF,%rsi
    and %rax,%rsi
    sal $32,%rsi
    mov $0xFFFFFFFF00000000,%rdx
    and %rax,%rdx
    sar $32,%rdx
    or %rdx,%rsi
    mov %rsi,%rax
    ret