the polymorphic engine skeleton so far

engine:
mov rcx, 4

call prng_seed
eloop:
; copy address in lookup table iterator
mov r9, qword [r8]

; flip a coin
call prng
and rax, 2

; modify operation
jnz b_jmp15

shr r10, 32
mov dword [r9], r10d
jmp end_jmp15
b_jmp15:
mov dword [r9], r10d
end_jmp15:

; flip a coin
call prng
and rax, 2

; shift in nops if zero
jnz no_shift
shl dword [r9], 16
or dword [r9], 0x9090
no_shift:

; iterate to next address
add r8, 8
loop eloop

ret