Category : Printer + Display Graphics
Archive   : AI32BT.ZIP
Filename : XBITASM.ASM

; Xbitasm.asm by Mark C. Peterson, CompuServe [70441,3353]

_TEXT SEGMENT BYTE PUBLIC 'CODE'
ASSUME CS:_TEXT

;int near _cdecl XBitShift(XBIT x, int XBytes, int ShiftBits)
x equ [bp + 6]
XBytes equ [bp + 8]
ShiftBits equ [bp + 10]

PUBLIC _XBitShift
_XBitShift PROC FAR
push bp
mov bp, sp
push si
xor ax, ax
mov bx, ShiftBits
or bx, bx
jz ExitXBitShift
jns ShiftXBitsLeft
neg bx

ShiftXBitsRight:
mov si, x
mov cx, XBytes
add si, cx
clc

ShiftNextByteRight:
dec si
rcr BYTE PTR [si], 1
loop ShiftNextByteRight

dec bx
jnz ShiftXBitsRight
jmp ExitXBitShift

ShiftXBitsLeft:
mov si, x
mov cx, XBytes
clc

ShiftNextByteLeft:
rcl BYTE PTR [si], 1
inc si
loop ShiftNextByteLeft

adc ax, 0
dec bx
jnz ShiftXBitsLeft

ExitXBitShift:
pop si
pop bp
ret
_XBitShift ENDP



;void near _cdecl XBitNegate(XBIT x, int XBytes);
x equ [bp + 6]
XBytes equ [bp + 8]

PUBLIC _XBitNegate
_XBitNegate PROC FAR
push bp
mov bp, sp
push si
xor ax, ax
mov si, x
mov cx, XBytes
dec cx
add si, cx
cmp WORD PTR [si], 8000h
jne Negate
ChkNextWord:
dec si
dec si
cmp WORD PTR [si], 0
jne Negate
loop ChkNextWord

add si, XBytes
dec si
mov BYTE PTR [si], 0
inc ax
jmp ExitXBitNegate

Negate:
mov si, x
mov cx, XBytes
clc

NegateNextByte:
not WORD PTR [si]
adc WORD PTR [si], ax
inc si
inc si
dec cx
loop NegateNextByte

ExitXBitNegate:
pop si
pop bp
ret
_XBitNegate ENDP

_TEXT ENDS


END