disassembly of various factorial implementation.

(PROCLAIM '(OPTIMIZE (SPEED 3) (SAFETY 0) (DEBUG 0)))

(DEFUN FACT1 (X)
  "factorial, using DO"
  (DECLARE (FIXNUM X))
  (DO ((FACT-N 1 (THE FIXNUM (* FACT-N N)))
       (N      1 (1+ N)))
      ((> N X) FACT-N)
    (DECLARE (FIXNUM FACT-N N))))

; disassembly for FACT1
; 0B2DB0CA:       B904000000       MOV ECX, 4                 ; no-arg-parsing entry point
;       CF:       B804000000       MOV EAX, 4
;       D4:       EB0D             JMP L1
;       D6: L0:   C1F902           SAR ECX, 2
;       D9:       0FAFC8           IMUL ECX, EAX
;       DC:       C1F802           SAR EAX, 2
;       DF:       40               INC EAX
;       E0:       C1E002           SHL EAX, 2
;       E3: L1:   39D0             CMP EAX, EDX
;       E5:       7EEF             JLE L0
;       E7:       8BD1             MOV EDX, ECX
;       E9:       8D65F8           LEA ESP, [EBP-8]
;       EC:       F8               CLC
;       ED:       8B6DFC           MOV EBP, [EBP-4]
;       F0:       C20400           RET 4


(DEFUN FACT2 (X)
  "factorial, using LOOP"
  (DECLARE (FIXNUM X))
  (LOOP
     :FOR N      :OF-TYPE FIXNUM :FROM 1 :TO   X
     :AND FACT-N :OF-TYPE FIXNUM :=    1 :THEN (* FACT-N N)
     :FINALLY    (RETURN  FACT-N)))
  
; disassembly for FACT2
; 0B6A658A:       B804000000       MOV EAX, 4                 ; no-arg-parsing entry point
;       8F:       31C9             XOR ECX, ECX
;       91:       B904000000       MOV ECX, 4
;       96:       EB13             JMP L1
;       98: L0:   8BD8             MOV EBX, EAX
;       9A:       C1FB02           SAR EBX, 2
;       9D:       43               INC EBX
;       9E:       C1F902           SAR ECX, 2
;       A1:       0FAFC8           IMUL ECX, EAX
;       A4:       8D049D00000000   LEA EAX, [EBX*4]
;       AB: L1:   39D0             CMP EAX, EDX
;       AD:       7EE9             JLE L0
;       AF:       8BD1             MOV EDX, ECX
;       B1:       8D65F8           LEA ESP, [EBP-8]
;       B4:       F8               CLC
;       B5:       8B6DFC           MOV EBP, [EBP-4]
;       B8:       C20400           RET 4

(DEFUN FACT3 (X)
  (DECLARE (FIXNUM X))
  (THE FIXNUM
    (IF (= X 1)
        1
        (* X (FACT3 (- X 1))))))

; disassembly for FACT3
; 0B0FAD55: L0:   83F904           CMP ECX, 4                 ; no-arg-parsing entry point
;       58:       750E             JNE L2
;       5A:       B804000000       MOV EAX, 4
;       5F: L1:   8D65F8           LEA ESP, [EBP-8]
;       62:       8B6DFC           MOV EBP, [EBP-4]
;       65:       C20400           RET 4
;       68: L2:   894DF4           MOV [EBP-12], ECX
;       6B:       8BC1             MOV EAX, ECX
;       6D:       83E804           SUB EAX, 4
;       70:       8BD0             MOV EDX, EAX
;       72:       8BDD             MOV EBX, EBP
;       74:       8BC4             MOV EAX, ESP
;       76:       83EC20           SUB ESP, 32
;       79:       8BCA             MOV ECX, EDX
;       7B:       8958FC           MOV [EAX-4], EBX
;       7E:       8BE8             MOV EBP, EAX
;       80:       C745F889AD0F0B   MOV DWORD PTR [EBP-8], 185576841
;       87:       EBCC             JMP L0
;       89:       8B4DF4           MOV ECX, [EBP-12]
;       8C:       C1F902           SAR ECX, 2
;       8F:       0FAFC8           IMUL ECX, EAX
;       92:       8BC1             MOV EAX, ECX
;       94:       EBC9             JMP L1

(DEFUN FACT4 (X)
  (DECLARE (FIXNUM X))
  (LABELS ((FACT4-SUB (N FACT-N)
             (DECLARE (FIXNUM N FACT-N)) 
             (IF (= N 1)
                 FACT-N
                 (FACT4-SUB (1- N) (THE FIXNUM (* FACT-N N))))))
    (FACT4-SUB X 1)))
                 
; disassembly for FACT4
; 0B472274:       B904000000       MOV ECX, 4                 ; no-arg-parsing entry point
;       79:       EB24             JMP L2
;       7B: L0:   83F804           CMP EAX, 4
;       7E:       750C             JNE L1
;       80:       8BD1             MOV EDX, ECX
;       82:       8D65F8           LEA ESP, [EBP-8]
;       85:       F8               CLC
;       86:       8B6DFC           MOV EBP, [EBP-4]
;       89:       C20400           RET 4
;       8C: L1:   8BD0             MOV EDX, EAX
;       8E:       C1FA02           SAR EDX, 2
;       91:       83EA01           SUB EDX, 1
;       94:       C1F902           SAR ECX, 2
;       97:       0FAFC8           IMUL ECX, EAX
;       9A:       8BC2             MOV EAX, EDX
;       9C:       C1E002           SHL EAX, 2
;       9F: L2:   EBDA             JMP L0