OpenVMS Source-Code Demos

PEEK_BYTE_VAX.MAR

;--------------------------------------------------------------------------------
; Title  : Peek_byte_vax.mar
; Author : Neil S. Rieck (Kitchener/Waterloo/Cambridge, Ontario, Canada)
; Created: 1999.11.12
;
; Notes:
; 1. This VAX assembly language function peeks (byte wise) into a memory location
; 2. It is tested for use with VAX-BASIC (see peek_demo1.bas)
; 3. parameters are passed here via register ap (argument pointer) a.k.a. r12
; 4. results are returned via r0 (and sometimes r1)
;--------------------------------------------------------------------------------
	.entry  peek_byte_vax,^M<>	; function name is PEEK_BYTE_VAX (null entry mask)
	clrq    r0			; clear both r0 + r1 (cuz q = 64 bit)
	movl    @4(ap),r2		; passed parameter #1 is address of data
	movb    (r2),r0			; do an indirect byte fetch into r0
	ret				; return to calling program
	.end

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Neil Rieck
Kitchener - Waterloo - Cambridge, Ontario, Canada.