asm汇编语言源代码之-获取环境变量

提供1个子程序:

　　1. 读取环境变量 GETENVSTR

具体功能及参数描述如下

GETENVSTR PROC　FAR ;IN:　DS=PSP SEG. ;　　 ES:BX -> ENV VAR NAME ;OUT: DS:DX -> ENV VAR VALUE; IF DX=0FFFFH, NOT FOUND

 

; more source code at http://www.ahjoe.com/source/srcdown.asp

        PUBLIC  GETENVSTR

CODE    SEGMENT
        ASSUME  CS:CODE
GETENVSTR PROC  FAR
;IN:  DS=PSP SEG.
;     ES:BX -> ENV VAR NAME
;OUT: DS:DX -> ENV VAR VALUE; IF DX=0FFFFH, NOT FOUND

        PUSH    AX
        PUSH    BX
        PUSH    SI
        PUSH    DI

        XOR     DI, DI
        MOV     DX, BX

        MOV     DS, DS:[2CH]
REPEAG:
        MOV     BX, DX
FINDREP:
        MOV     AL, ES:[BX]
        CMP     AL, DS:[DI]
        JNZ     NOTEQU
        INC     BX
        INC     DI
        JMP     FINDREP

NOTEQU:
        CMP     BYTE PTR DS:[DI], '='
        JNZ     NOTEQUCH
        CMP     BYTE PTR ES:[BX], 0
        JZ      FOUNDIT
NOTEQUCH:
        CMP     BYTE PTR DS:[DI], 0
        JZ      LOCAZERO
        INC     DI
        JMP     NOTEQUCH
LOCAZERO:
        INC     DI
        CMP     BYTE  PTR DS:[DI], 0
        JNZ     REPEAG
        MOV     DX, 0FFFFH
        JMP     GETENVOK
FOUNDIT:
        MOV     DX, DI
        INC     DX
GETENVOK:
        POP     DI
        POP     SI
        POP     BX
        POP     AX
        RETF
GETENVSTR ENDP
CODE    ENDS
        END     GETENVSTR