Duff's device, as emitted by GCC[0], is a bit on the verbose side but still quite neat. In particular the single-instruction computed goto that uses a look-up t

Duff's device, as emitted by GCC[0], is a bit on the verbose side but still quite neat. In particular the single-instruction computed goto that uses a look-up table made up of 8 quad-words, filled in by the linker. Note the '.section .rodata' directive which actually places the quads pointers, seemingly interleaved with code, in a read-only data section. Note also the dec/test/jle instructions implementing the while loop occur before the last of the eight copy operations, and interleaved with the next-to-last copy operation. duff: .LFB0: .cfi_startproc lea eax, [rdi+7] mov r8d, 8 mov rcx, rdx cdq idiv r8d mov r9d, eax mov eax, edi cdq idiv r8d cmp edx, 7 ja .L2 mov edx, edx jmp [QWORD PTR .L4[0+rdx*8]] .section .rodata .align 8 .align 4 .L4: .quad .L3 .quad .L5 .quad .L6 .quad .L7 .quad .L8 .quad .L9 .quad .L10 .quad .L11 .text .L11: mov al, BYTE PTR [rsi] inc rsi mov BYTE PTR [rcx], al .L10: mov al, BYTE PTR [rsi] inc rsi mov BYTE PTR [rcx], al .L9: mov al, BYTE PTR [rsi] inc rsi mov BYTE PTR [rcx], al .L8: mov al, BYTE PTR [rsi] inc rsi mov BYTE PTR [rcx], al .L7: mov al, BYTE PTR [rsi] inc rsi mov BYTE PTR [rcx], al .L6: mov al, BYTE PTR [rsi] inc rsi mov BYTE PTR [rcx], al .L5: mov al, BYTE PTR [rsi] dec r9d inc rsi test r9d, r9d mov BYTE PTR [rcx], al jle .L2 .L3: mov al, BYTE PTR [rsi] inc rsi mov BYTE PTR [rcx], al jmp .L11 .L2: ret .cfi_endproc ___ edit: formatting, sigh [0] v 7.3.0 64bit; gcc -S -Os -masm=intel