; Get a hard copy on Amazon for $10.

[0x24]
dec [xchg rax,rax] inc 
    mov      rbx,rax
    mov      rsi,rax
.loop:
    mul      rbx
    mov      rcx,rax

    sub      rax,2
    neg      rax
    mul      rsi
    mov      rsi,rax

    cmp      rcx,1
    ja       .loop
.exit_loop:
; xorpd(&)xorpd.net