OS_Develop/dos_compilers
OS_Develop/dos_compilers
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performance; use 8-bit mul/div

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This commit is contained in:
davidly 2024-07-24 21:33:05 -07:00
parent 53e84f4c72
commit 1b9b8b0959
2 changed files with 38 additions and 46 deletions
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42
Borland Turbo Assembler v32/E.ASM
View File

@ -59,39 +59,35 @@ true equ 1
false equ 0
digits equ 200
dataseg segment para public 'data'
assume ds: dataseg
e_dataseg segment para public 'data'
assume ds: e_dataseg
crlfmsg db 13,10,0
donemsg db 'done',13,10,0
align 16
array db digits dup( ? )
dataseg ends
e_dataseg ends
.code
start:
mov ax, dataseg
mov ax, e_dataseg
mov ds, ax
; why is the loop backwards? no idea.
; while n > 0 do begin
; a[ n ] := 1;
; n := n - 1;
; end;
; register bh is n. di is a[]. bl is a constant 1
mov bl, 1
mov bh, digits - 1
mov di, offset array + digits - 1
ainit:
mov byte ptr [ di ], bl
dec di
dec bh
jnz ainit
mov al, 1
mov ah, 1
push ds
pop es
mov di, offset array
mov cx, ( digits / 2 )
cld
rep stosw
; a[ 1 ] := 2;
; a[ 0 ] := 0;
@ -99,6 +95,7 @@ start:
mov di, offset array
mov byte ptr[ di + 1 ], 2
mov byte ptr[ di ], 0
mov cl, 10
; register bx is n. register si is high. register di is x at the start of each inner loop
@ -110,16 +107,15 @@ start:
xor di, di ; x := 0;
innerloop:
xor dx, dx
mov ax, di
div bx ; computes both x MOD n and x DIV n. dx has remainder, ax has result
mov di, ax ; save the result of the division in di. ah is guaranteed to be 0.
div bl ; computes both x MOD n and x DIV n. ah has remainder, al has quotient
mov byte ptr[ offset array + bx ], dl ; a[ n ] := x MOD n;
mov byte ptr[ offset array + bx ], ah ; a[ n ] := x MOD n;
xor ah, ah
mov di, ax ; save the quotient in di.
mov al, byte ptr [ offset array + bx - 1 ] ; load a[ n - 1 ] into al
mov cx, 10
mul cx
mov al, byte ptr [ offset array + bx - 1 ] ; load a[ n - 1 ]
mul cl
add di, ax ; x := 10 * a[ n - 1 ] + x DIV n;
dec bx ; n := n - 1;

42
Microsoft MASM v5/E.ASM
View File

@ -59,39 +59,35 @@ true equ 1
false equ 0
digits equ 200
dataseg segment para public 'data'
assume ds: dataseg
e_dataseg segment para public 'data'
assume ds: e_dataseg
crlfmsg db 13,10,0
donemsg db 'done',13,10,0
align 16
array db digits dup( ? )
dataseg ends
e_dataseg ends
.code
start:
mov ax, dataseg
mov ax, e_dataseg
mov ds, ax
; why is the loop backwards? no idea.
; while n > 0 do begin
; a[ n ] := 1;
; n := n - 1;
; end;
; register bh is n. di is a[]. bl is a constant 1
mov bl, 1
mov bh, digits - 1
mov di, offset array + digits - 1
ainit:
mov byte ptr [ di ], bl
dec di
dec bh
jnz ainit
mov al, 1
mov ah, 1
push ds
pop es
mov di, offset array
mov cx, ( digits / 2 )
cld
rep stosw
; a[ 1 ] := 2;
; a[ 0 ] := 0;
@ -99,6 +95,7 @@ start:
mov di, offset array
mov byte ptr[ di + 1 ], 2
mov byte ptr[ di ], 0
mov cl, 10
; register bx is n. register si is high. register di is x at the start of each inner loop
@ -110,16 +107,15 @@ start:
xor di, di ; x := 0;
innerloop:
xor dx, dx
mov ax, di
div bx ; computes both x MOD n and x DIV n. dx has remainder, ax has result
mov di, ax ; save the result of the division in di. ah is guaranteed to be 0.
div bl ; computes both x MOD n and x DIV n. ah has remainder, al has quotient
mov byte ptr[ offset array + bx ], dl ; a[ n ] := x MOD n;
mov byte ptr[ offset array + bx ], ah ; a[ n ] := x MOD n;
xor ah, ah
mov di, ax ; save the quotient in di.
mov al, byte ptr [ offset array + bx - 1 ] ; load a[ n - 1 ] into al
mov cx, 10
mul cx
mov al, byte ptr [ offset array + bx - 1 ] ; load a[ n - 1 ]
mul cl
add di, ax ; x := 10 * a[ n - 1 ] + x DIV n;
dec bx ; n := n - 1;