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n-factorial.s
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n-factorial.s
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datas segment
buff db 6, ?, 6 dup(?)
Factorial dw 1, 999 dup(0) ;阶乘，初值为1
TempF dw 1000 dup(0) ;临时阶乘
Divisor dw 1000 dup(0) ;除数
Quotient dw 1000 dup(0) ;商
Result db 1000 dup(0) ;阶乘结果的非压缩BCD码形式
N dw 0 ;N的2进制形式
i dw 1 ;2进制Factorial的字数
j dw 0 ;十进制阶乘的位数
a dw 1, 10, 100, 1000, 10000 ;Buff中字符转为N时用到
b dw ?
msg1 db "Please input N: $"
msg2 db 0ah, 0dh, "Press any key to exit...$"
msg3 db 0ah, 0dh, "N!=$"
datas ends
stacks segment
;
stacks ends
codes segment
assume cs: codes, ds: datas, ss: stacks, es: datas
start:
mov ax, datas
mov ds, ax
mov es, ax
Main:
call Input ;输入N
call Factor ;计算N!
call Convert ;将2进制Factorial转为非压缩BCD码Result
call Output
jmp Final
;------------------------------------------------------------------------------
;输入字符型N，转为2进制
Input:
lea dx, msg1
mov ah, 9
int 21h
lea dx, buff
mov ah, 10
int 21h
lea di, a ;将输入字符串转化为整数存入N
mov ch, 0
mov cl, buff+1
mov si, cx
L0: mov ah, 0
mov al, buff[si+1]
sub al, 30h
dec si
mov bx, [di]
mul bx
add N, ax
add di, 2
loop L0
ret
;输入字符型N，转为2进制
;------------------------------------------------------------------------------
;计算N!
Factor:
mov bx, 1
mov cx, N
L1: push cx
lea di, TempF
lea si, Factorial
mov cx, i
L2: mov ax, [si]
mov [di], ax
mov ax, 0
mov [si], ax
add si, 2
add di, 2
loop L2
lea di, TempF
lea si, Factorial
mov cx, i
L3: mov ax, [di]
mov dx, 0
mul bx
add [si], ax
adc [si+2], dx
add si, 2
add di, 2
loop L3
cmp dx, 0
jz N1
add i, 1
N1: inc bx
pop cx
loop L1
ret
;计算N!
;-----------------------------------------------------------------------------
;将2进制Factorial转为非压缩BCD码Result
Convert:
mov ax, i
mov bx, 2
mul bx
sub ax, 2
mov b, ax
L11: call setD ;设置除数
call div10
call Save
call cmpQz ;测试商是否为零
cmp ax, 0
jz N5
call movQF ;将商移入Factorial做下一步除法
call clQ ;商清零
jmp L11
N5:
ret
;..........................................
setD:
lea di, Quotient
mov cx, i
mov ax, 0
L10: mov [di], ax
add di, 2
loop L10
mov ax, 0a000h
mov [di-2], ax
ret
;..........................................
Div10:
mov bx, 16
mov ax, i
mul bx
sub ax, 3
mov cx, ax
L7: push cx
call CmpFD
jb N2
call SubFD
stc
jmp N3
N2: clc
N3: call QSHL
call DSHR
pop cx
loop L7
ret
;..........................................
Save:
lea si, Factorial
lea di, Result
mov ax, j
add di, ax
mov al, [si]
mov [di], al
lea di, j
mov ax, 1
add [di], ax
ret
;..........................................
cmpQz:
lea si, Divisor
mov cx, i
L15: mov ax, [si]
cmp ax, 0
jnz N4
add si, 2
loop L15
N4: ret
;..........................................
movQF:
lea di, Factorial
lea si, Divisor
mov cx, i
L9: mov ax, [si]
mov [di], ax
add si, 2
add di, 2
loop L9
ret
;...........................................
clQ:
lea di, Divisor
mov cx, i
mov ax, 0
L12: mov [di], ax
add di, 2
loop L12
ret
;..........................................
CmpFD:
lea di, Quotient
lea si, Factorial
add di, b
add si, b
mov cx, i
std
repz cmpsw
ret
;..........................................
SubFD:
lea di, Factorial
lea si, Quotient
mov cx, i
clc
L4: mov bx, [si]
sbb [di], bx
inc si
inc si
inc di
inc di
loop L4
ret
;..........................................
QSHL:
lea si, Divisor
mov cx, i
L5: rcl word ptr[si], 1
inc si
inc si
loop L5
ret
;..........................................
DSHR:
lea si, Quotient
add si, b
mov cx, i
clc
L6: rcr word ptr[si], 1
dec si
dec si
loop L6
ret
;将2进制Factorial转为非压缩BCD码Result
;-----------------------------------------------------------------------------
;输出!
Output:
lea dx, msg3
mov ah, 9
int 21h
lea di, Result
mov cx, j
add di, cx
sub di, 1
L14: mov dl, [di]
cmp dl, 0
jnz L13
dec di
loop L14
L13: mov dl, [di]
add dl, 30h
mov ah, 2
int 21h
dec di
loop L13
ret
;输出N!
;------------------------------------------------------------------------------
Final:
lea dx, msg2
mov ah, 9
int 21h
mov ah, 1
int 21h
mov ah, 4ch
int 21h
codes ends
end start