Microsoft KB Archive/58827

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DSPACE.ASM from COBOL 2.x User’s Guide Is Incomplete; Hangs

PSS ID Number: Q58827 Article last modified on 04-20-1993

2.00 2.10 2.20 MS-DOS

The information in this article applies to:
- Microsoft COBOL for MS-DOS, versions 2.0, 2.1, and 2.2

Summary: Four lines are missing from the bottom of the assembly language program DSPACE.ASM on Pages 103-104 of the “Microsoft COBOL Compiler for MS-DOS: User’s Guide” for Versions 2.0, 2.1, and 2.2. The assembly routine, when assembled as the book states, often hangs the machine. You must add the following lines after the “spret:” label: spret: pop bp ret END_CSEG DSPACE END

More Information:

The complete corrected code for DSPACE.ASM is as follows: ;********************************************* ; Contains a routine to call the MS-DOS Get ; Free Disk Space function. Zero is returned ; in the third parameter in case of error. ;********************************************* include userseg.mac ; ;Structure for accessing parameters on stack ; DYNS2 STRUC DW ? ;Pushed BP. DD ? ;Long return address. ARG3 DW ? ;Parameter number 3. ARG2 DW ? ;Parameter number 2. ARG1 DW ? ;Parameter number 1. DYNS2 ENDS MSDOS EQU 21H ;standard MS-DOS entry point SPACE EQU 36H ;get disk free space function START_DSEG DSPACE savbc dw ? ;bytes per disk cluster savdx dw ? ;temporary register area END_DSEG DSPACE START_CSEG DSPACE push bp ;use bp to point to arguments mov bp,sp mov bx,[bp].arg1 ;get addr of arg1 (drive number) mov dx,[bx] ;get drive to dl xchg dh,dl ;COBOL COMP-0 bytes reversed mov ah,SPACE ;call MS-DOS function INT MSDOS ;on return: ; bx = # of free clusters on drive ; dx = total # of clusters on drive ; cx = bytes of sector ; ax = sectors per cluster or FFFF if error cmp ax, 0FFFFH ;error? jz error mov savdx,dx ;multiply wipes out dx, so save it mul cx ;bytes/clusters in ax jc error ;should never overflow, but… mov savbc,ax ;save for later use mul bx ;low order result in ax, ;high order in dx mov bx,[bp].arg2 ; get addr od COMP-4 free space ; store 4 byte value in this order: ; least significant word (in dx), ; then most significant word (in ax) ; with bytes of each word reversed xchg dh,dl ;COBOL COMP-0 bytes reversed mov [bx],dx xchg ah,al ;COBOL COMP-0 bytes reversed mov [bx+2],ax mov ax,savbc ;restore ax and dx mov dx,savdx mul dx ;low order result in ax, ;high in dx mov bx,[bp].arg3 ;get addr of COMP-4 total space ;store 4 byte variable xchg ah,al ;COBOL COMP-0 bytes reversed mov [bx+2],ax jmp spret ;done… error: xor ax,ax ;zero arg3 to indicate error mov bx,[bp].arg3 mov [bx],ax mov [bx+2],ax ;**** modified lines follow: spret: pop bp ret END_CSEG DSPACE END

Additional reference words: 2.00 2.10 2.20 Copyright Microsoft Corporation 1993.