Attempting to decode: f3 66 ad 
iclass REP_LODSW	category STRINGOP	ISA-extension BASE	ISA-set I86
instruction-length 3
operand-width 16
effective-operand-width 16
effective-address-width 32
stack-address-width 32
iform-enum-name REP_LODSW
iform-enum-name-dispatch (zero based) 0
iclass-max-iform-dispatch 1
Nominal opcode position 2
Nominal opcode 0xad
Operands
#   TYPE               DETAILS        VIS  RW       OC2 BITS BYTES NELEM ELEMSZ   ELEMTYPE   REGCLASS
#   ====               =======        ===  ==       === ==== ===== ===== ======   ========   ========
0   REG0               REG0=AX SUPPRESSED  CW         W   16     2     1     16        INT        GPR
1   MEM0           (see below) SUPPRESSED  CR         W   16     2     1     16        INT    INVALID
2  BASE0             BASE0=ESI SUPPRESSED RCW       ASZ   32     4     1     32        INT        GPR
3   REG1              REG1=ECX SUPPRESSED RCW       ASZ   32     4     1     32        INT        GPR
4   REG2           REG2=EFLAGS SUPPRESSED   R         Y   32     4     1     32        INT      FLAGS
Memory Operands
  0    read SEG= DS BASE= ESI/GPR  ASZ0=32
  MemopBytes = 2
FLAGS:
   reads-rflags df-tst 
       read:                            df  mask=0x400
    written:                                mask=0x0
  undefined:                                mask=0x0
ATTRIBUTES: FIXED_BASE0 REP 
REAL REP 	corresponding no-rep iclass: LODSW
F3 PREFIX
66-OSZ PREFIX
ANY 66 PREFIX
Number of legacy prefixes: 2 
ISA SET: [I86]