Compile learning notes for beginners (14th) -- directly address the table

Getting started with crazy summer vacation Study Notes (14th)-direct address table

Reference: chapter 16th of Assembly Language

1. Description unit length label

Common labels: a, B

assume cs:codecode segmenta:db 1,2,3,4,5,6,7,8b:dw 0start:mov si,offset amov di,offset bmov ah,0mov cx,8s:mov al,cs:[si]add cs:[di],axinc siloop smov ax,4c00hint 21hmov ax,4c00hint 21hcode endsend start

Take a closer look at the labels of the following code. The numbers A and B below are not followed by colons. They are labels that can describe the unit length. Also called data label

assume cs:codecode segmenta db 1,2,3,4,5,6,7,8b dw 0start:mov si,offset amov ah,0mov cx,8s:mov al,a[si]add b,axinc siloop smov ax,4c00hint 21hmov ax,4c00hint 21hcode endsend start

We can:

MoV ax, BX is equivalent to mov ax, CS: [8]

MoV B, 2 is equivalent to mov word PTR Cs: [8], 2

Inc B is equivalent to INC word PTR Cs: [8]

MoV Al, a [Si] is equivalent to mov Al, CS: 0 [Si]

MoV Al, a [3] is equivalent to mov Al, CS: 0 [3]

But the following is wrong.

MoV Al, B because B is DW, font

Add B, Al

2. Use data labels in other segments

A common label with a ":" can only be defined in a code segment. Data labels can be used in other segments.

Example: If you want to write DS: B as B directly, you must add Cs: data after assume.

assume cs:code,ds:datadata segmenta db 1,2,3,4,5,6,7,8b dw 0data endscode segmentstart:mov ax,datamov ds,axmov si,offset amov ah,0mov cx,8s:mov al,a[si]add b,axinc siloop smov ax,4c00hint 21hmov ax,4c00hint 21hcode endsend start

3. Direct addressing table

We can create a table and use the table query method to speed up processing.

Example: A hexadecimal number character is displayed on the screen. The character here is used for a table.

Assume Cs: codecode segmentstart: mov Al, 0 ehcall showbytemov ax, 4c00hint 21 hshowbyte: JMP short showtable dB 'hangzhou'; Tables Table show: Push bxpush esmov ah, alshr ah, 1; 4-digit shift to the right, 4-digit high in AH, 4th-digit SHR ah, 1shr ah, 1shr ah, 1and Al, 00001111 bmov BL, ahmov BH, 0mov Ah in Al, table [BX] mov BX, 0b800hmov es, bxmov ES: [160*12 + 40*2], ahmov BL, AlMoV BH, 0mov Al, table [BX] mov ES: [160*12 + 40*2 + 2], alpop ESPOP bxretcode endsend start

We can also store the subprogram address in the direct addressing table to facilitate the calling of different subprograms.

Compile learning notes for beginners (14th) -- directly address the table