装配计算正弦示例。NASM 16 DOS

如果我理解正确的话，您想在没有任何平移和缩放的情况下绘制正弦波。因此，你可以把 作为你的坐标，你从函数中得到的值就是你的坐标。angleXf(x) = sin xY

; EAX = in &CooordX
; EBX = out &CoordY
SinX:
    fld     qword [eax]           ; st(0) = angle 
    fsin                         ; st(0) = sin(angle)
    fstp    qword [ebx]           ; *ebx = sin(angle) 
    ret

现在假设你想画一个波浪。这意味着在绘制最后一个像素时，（全波）必须完全为真。屏幕宽度为 640 像素，绘图循环中的单个步骤是 。其余的很简单。x == 2*PI radx2*PI/640 = 0.009817

;CONSTANTS:
step: dw 320        ; 2/640 = 320, omitted PI
imgWidth: dw 640    ; 640px
imgHeight: dw 480/2 ; 480px on half, because Y also gets negative

;VARIABLES:
y: dw 0     ; a tmp place to save Y

DrawWave:
    mov ebx, y  ; EBX = &y
    mov ecx, 0

    ; let st(1) = 2*PI/640
    fldpi               ; st(0) = PI
    fidiv dword [step]  ; st(0)/320 = 0.009817...
    fldz                ; st(0) = 0.0, st(1) = 0.009817...

    .loop:
        fld st(0)   ; duplicate the x on the top
        fsin        ; st(0) = sin x

        fimul dword [imgHeight]     ; st(0) = y*240
        fiadd dword [imgHeight]     ; eliminate negative coordinate by translating the wave vertically          
        fistp dword [y]             ; store y to ´y´

        fadd st(0), st(1)           ; add the step value to x, doing the step

        ;draw pixel at [*EAX:ECX]
        call DrawPixel

        inc ecx
        cmp ecx, 640    ; perform 640 steps to draw a single sine wave
        jl .loop

        fstp st(0)  ;clean up
        fstp st(0)  ;clean up
    ret

; EBX = in &CoordY
; ECX = CoordX  
DrawPixel:
    ; draw a pixel at [*EBX:ECX]
    ret

我的两分钱;-）。X 是度数，Y 是缩放 （*50） 正弦辐射点。（隐藏的）X 轴位于第 100 行。

segment stack stack
    resb 0x1000

segment .data
    ; no data

segment .code
..start:
main:
    mov ax, data            ; Initialize DS (needed for .exe-program)
    mov ds, ax
    mov ax, 0x0A000         ; Segment to video memory
    mov es, ax

    mov ax, 13h
    int 10h                 ; switch to 320x200 mode

    mov cx, 0
    .l1:
    push cx                 ; store CX
    call get_sine
    add ax, 100             ; shift Y to position of X-axis (100)
    mov bx, cx
    call vector_to_memory
    mov di, ax
    mov al, 0x0F            ; white
    mov [es:di], al         ; put pixel
    pop cx                  ; restore CX
    inc cx                  ; CX = CX + 1
    cmp cx, 320             ; right boarder reached?
    jne .l1                 ; no, next degree

    xor ah, ah
    int 16h                 ; keyboard (wait for key)
    mov ax, 3
    int 10h                 ; go to text mode
    mov ax, 0x4C00
    int 21h                 ; return to DOS, exit code 0

get_sine:                   ; Args: CX = angle (degree!)
    push cx                 ; = sub sp, 2 (local stack space), mov [sp], cx
    mov bp, sp              ; BP = SP (local stack space) for FPU-accesses
    fild word [bp]          ; ST(0): CX
    fldpi                   ; ST(0)=Pi, ST(1)=CX
    fmulp                   ; ST(0)=Pi*CX
    mov word [bp], 180
    fidiv word [bp]         ; ST(0)=(Pi*CX)/180 (formula for degree to rad)
    fsin                    ; ST(0)=sine (rad)
    mov word [bp], 50       ; Scale the result by 50 (e.g. 0.8 => 40.0)
    fimul word [bp]         ; ST(0)=sine*scale
    fchs                    ; reverse sign because video counts from top to bottom
    fistp word [bp]         ; store integer with rounding to local stack space
    pop ax                  ; AX = local stack space
    ret                     ; Return: AX = Y (signed!)

vector_to_memory:           ; Args: BX = X, AX = Y
    push dx                 ; mul changes dx too
    mov cx, 320             ; video mode width
    mul cx                  ; DX:AX = AX * CX
    add ax, bx              ; left indentation
    pop dx
    ret                     ; Return: AX = offset in memory

另一种方法是创建和使用自己的正弦/余弦表，我们只能将该表存储到文件中一次，并多次加载和使用它。以下示例演示如何创建自己的正弦/余弦表。

      Grad    = 360
      Endtab  = 450

segment .data

SINTAB DB Endtab DUP (?,?,?,?)

TEIL   DW 180, ?
I      DW 0, 0

TABNAM DB "Sin.tab"

segment .code

START:    mov     ax, data
          mov     ds, ax
          finit
          call TABLE
          mov     dx, TABNAM
          call MAKDAT
          xor     dx, dx
          mov     cx, Endtab*4
          call WRITE
          call CLOSE
          mov     ax, 4C00h
          int   21h

TABLE:    xor     di, di          ; Create sine table
TAB:      fldpi
          fimul  DWORD[I]
          fidiv  DWORD[TEIL]      ; by 180(INT)
          fsin
          fstp   DWORD[di]
          inc    WORD[I]
          add     di, 4
          cmp    WORD[I], Endtab
          jnz TAB
          ret

MAKDAT:   mov     ah, 3Ch
          xor     cx, cx
          int  21h       ; we hope that no error occur
          mov     bx, ax ; ....but better insert a handling for
          ret

WRITE:    mov     ah, 40h
          int   21h       ; ....also here
          ret

CLOSE:    mov     ah, 3Eh
          int   21h
          ret

还可以创建和使用整数正弦/余弦表。但是它的处理有点不同，因为正弦/余弦值是相乘的，所以我们必须用相同的乘数将我们想要计算的值相乘，最后我们必须计算结果。

      Grad    = 360 * 2
      Endtab  = 450 * 2
      Foktor  = 10000h   ; for to replace/shift the floating point of the value

segment .data

SINTAB DB Endtab DUP (?,?,?,?)
TEIL   DW Grad/2, ?
I      DW 0, 0
FAKT   DD Foktor
TABNAM DB "SinInt.tab", 0

segment .code

START:    ; same main-routine

TABLE:    xor     di, di     ; subroutine for to create an integer table
TAB:      fldpi
          fimul  DWORD[I]
          fidiv  DWORD[TEIL]
          fsin
          fimul  DWORD[FAKT]
          fistp  DWORD[di]
          inc    WORD[I]
          add     di, 4
          cmp    WORD[I], Endtab
          jnz TAB
          ret

; same subroutines for create, write and store file

为了获得更高的计算精度（例如，为了防止出现孔洞，屏幕分辨率更高），我们可以简单地将循环计数器的 360 度值加倍。