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The UCR Standard Assembly Language Library

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This article contains the following executables: UCRASM.ARC

Randy is the designer of numerous hardware and software projects, including assemblers. In addition to consulting, he is currently an instructor in computer science at California Polytechnic University, Pomona and UC Riverside. He can be contacted at 16217 Sunset Trail, Riverside, CA 92506.

Given the obvious benefits of space and speed, it's sad that assembly language has such a bad reputation. Some people cite portability, others complain about how hard it is to learn, but the real reason people don't write more code in assembly language can be summed up in one word: effort. Assembly language will never gain ground against high-level languages unless we can make it easier to program.

There are many reasons why people feel that programming in assembly language is much more difficult than programming in a high-level language such as C. A few points, however, top the list:

  • Assembly language programmers usually "start from scratch" on new projects.
  • Good assembly language programming requires a completely new mind-set, and most programmers are uncomfortable with the steep learning curve.
  • There is no standardized set of library routines supplied with all assemblers (such as the standard C library). Commercial packages are available, but cost often prevents their universal acceptance.
The University of California Riverside (UCR) Standard Library for 80x86 assembly language programmers is an attempt to overcome these problems. First, the library provides a slate of important and useful high-level routines -- perfect for starting a new project. Second, the UCR StdLib routines mimic many of the C standard library routines, so anyone who has invested time learning the C standard library will feel right at home with the UCR StdLib. Finally, the library -- including source code -- is free to anyone who wants it.

I've had quite a bit of success teaching students assembly language at the University of California Riverside using this library. It definitely eases the transition from a high-level language to assembly. Of course, the best assembly language programs are not "C programs written with MOV instructions," but my experience shows that getting students to write real programs in assembly language as soon as possible improves the quality of their education. For professional assembly language programmers, the UCR Standard Library package provides the opportunity to write code in assembly which would be too kludgey in a high-level language (yes, assembly is more appropriate for many applications), but require too much unwritten support code in a typical assembly language application.

What's in the Library

While space restrictions prevent me from describing each entry in detail, a few examples will give you an idea of the types of routines available in the library. See Table 1, which lists the names and brief descriptions of all the routines currently in the library. I must emphasize that current means as of the writing of this article. There may be even more routines available by the time you read this. The library is in a state of constant flux.

Table 1: A brief description of the routines available in the UCR StdLib Package: The standard library routines are divided into nine distinct classes: input, output, file I/O, conversions, utility, string, memory management, character set, and floating point.

  Input Routines

  Getc              Reads a single character from the (library) standard
  GetcStdIn         Reads a single character from the DOS standard input.
  GetcBIOS          Reads a single character from the keyboard by calling

  SetInAdrs         }
  GetInAdrs         } Maintain pointers to the current input routine.  By
  PushInAdrs        } them around, you can redirect the input obtained
  PopInAdrs         } the Getc routine.

  Gets (m)          Reads a string from the keyboard.
  Scanf             Formatted input routine, similar to C.

  Output Routines

  Putc              Writes a single character to the (library) standard
  PutCR             Writes a CR/LF pair using Putc.
  PutcStdOut        Calls DOS to print a character to the DOS standard
  PutcBIOS          Calls BIOS to print a character to the display.

  GetOutAdrs,       }
  SetOutAdrs,       } Like the corresponding routines above, these
  PushOutAdrs,      } maintain the stdlib standard output pointers.
  PopOutAdrs-       }

  Puts              Prints string pointed at by ES:DI.
  Puth              Prints value in AL as two hex digits.
  Putw              Prints value in AX as four hex digits.
  Puti              Prints value in AX as signed decimal number.
  Putu              Prints value in AX as unsigned decimal number.
  Putl              Prints 32-bit value in DX:AX as signed decimal
  Putul             Prints 32-bit value in DX:AX as unsigned decimal
  PutlSize          Prints integer value in AX using CX print positions.
  PutUSize          Prints unsigned value in AX using CX print positions.
  PutLSize          Prints long integer value in DX:AX using CX print
  PutULSize         Prints unsigned long value in DX:AX using CX print
  Print             Prints zero-terminated literal string constant
                     following the call.
  Printf            Similar to the corresponding C routine.

  File I/O Routines

  Fcreate           Creates (and opens for writing) a new file.
  ES:DI                      points at the name.
  FOpen             Opens an existing file for reading or writing.
  ES:DI                      points at the name.
  FClose            Closes a file.

  FReadOn,          } Redirect the standard input routines so that they
  FReadOff          } their input from a file.
  FWriteOn,         } Redirect the standard output routines so that they
  FWriteOff         } their output to a file.

  FSeek             Moves the file pointer around in the file.
  DOSHandle         Converts STDLIB file handle to DOS file handle.
  FDelete           Deletes a file.
  FRename           Renames a file.

  Conversion Routines

  Atol  (2)         Converts ASCII string to long integer returned in
  Atoul (2)         Converts ASCII string to unsigned 32-bit value in
  Atou  (2)         Converts ASCII string to 16-bit unsigned integer in
  Atoh  (2)         Converts ASCII string of hex digits to 16-bit value in
  Atolh (2)         Converts ASCII string of hex digits to 32-bit value
                     in DX:AX.
  Atoi  (2)         Converts ASCII string to 16-bit signed integer in AX.

  Itoa  (2,m)       Converts signed integer value in AX to string.
  Utoa  (2,m)       Converts unsigned value in AX to string, similar to
  Htoa  (2,m)       Converts binary value in AL to exactly two hexadecimal
  Wtoa  (2,m)       Converts binary value in AX to exactly four
                     hexadecimal characters.
  Ltoa  (2,m)       Converts 32-bit signed value in DX:AX to string, like
  Ultoa (2,m)       Converts 32-bit unsigned value in DX:AX to string.
  Sprintf (m)       Performs in-core formatting operation, like its C
  Sscanf            Like the C sscanf routine.

  ToLower           If character in AL is upper case, converts it to lower
  ToUpper           Converts lower-case chars in AL to upper case.

  Utility Routines

  ISize             On input, AX contains signed decimal integer.  On
                    AX contains number of print positions this integer
                     would require (including sign).
  USize             Returns output size of unsigned value in AX.
  LSize             Returns output size of 32-bit signed value in DX:AX.
  ULSize            Returns output size of 32-bit unsigned value in DX:AX.
  IsAINum           Returns Z-flag set if character is alphanumeric.
  IsXDigit          Returns Z-flag set if character is a hex digit.

  IsDigit           Returns Z-flag set if character is a decimal digit.
  IsAlpha           Returns Z-flag set if character is alphabetic.
  IsLower           Returns Z-flag set if character is a lowercase
  IsUpper           Returns Z-flag set if character is an uppercase

  String Routines

  Strcpy (I)        Copies string from ES:DI to DX:SI (including 0 byte).
  StrDup (I)        Copies string from ES:DI to newly allocate storage on
                     heap.  Returns the pointer to the new string in ES:DI.
  StrLen            Computes the length of a string.
  Strcat (m, I, mI) Concatenates two strings.
  StrChr            Searches for a character within a string.
  StrStr (I)        Searches for a substring within a string.
  Strcmp (I)        Compares two strings.
  Strupr (m)        Converts all lowercase characters in string to upper
  Strlwr (m)        Converts all uppercase characters in string to lower
  Strset (m)        Overwrites all characters in string with character
                     passed in AL.
  Strspan (I)       Skips over characters in string which belong to a
                     specified set.  Returns number of skipped characters
                     in CX.
  Strcspan (I)      Like the routines above, but skips characters not in
                     the set.
  Strins (m, I,mI)  Inserts one string into another.
  Strdel (m)        Deletes characters from a string.
  StrRev (m)        Reverses characters in string (submitted by Mike

  Memory Management Routines

  MemInit           Initializes the memory manager.
  Malloc            Allocates blocks of memory.
  Realloc           Resizes an allocated block.
  Free              Deallocates a block allocated via malloc.
  Dupptr            Informs the memory manager that two different pointers
                     refer to the same block.  Free will not deallocate
                     the block until you call it once for each duplicated
  IsInHeap          Returns true if a pointer points anywhere within the
                     heap area.
  IsPtr             Returns true if ES:DI points at a currently allocated

  Character Set Routines

  Set               Macro which lets you define up to eight character sets.
  CreateSets        Allocates storage and intializes up to eight sets on
                     the heap.
   EmptySet          Sets a character set to the empty set.
  RangeSet          Builds character set from lower-bound and upper-bound
  AddStr (I)        Adds the characters in a string to a character set.
  RmvStr (I)        Removes characters specified in string from a character
  AddChar           Adds a single character (in AL) to a character set.
  RmvChar           Removes a single character from a character set.
  Member            Sets Z-flag if character in AL is a member of specified
                     character set.
  CopySet           Copies the bits from one set to another.
  SetUnion          Computes the union of two character sets.
  SetIntersect      Computes the intersection of two a character sets.
  SetDifference     Computes the set difference of two character sets.
  NextItem          Returns the ASCII code of the first item found in the
  RmvItem           Removes next available item from set and returns this

  Floating-Point Routines

  lsfpa             Loads floating-point accumulator (fpacc) with 32-bit
                     single precision value.
  ssfpa             Stores fpacc into a single precision variable.
  ldfpa             Loads fpacc from a 64-bit double precision variable.
  sdfpa             Stores fpacc from a double precision variable.
  lefpa (I)         Loads fpacc from an 80-bit extended precision variable.
  sefpa             Stores fpacc into an extended precision variable.
  lsfpo             Loads floating-point operand (fpop) from single
                     precision variable.
  ldfpo             Loads fpop from a double precision variable.
  lefpo (I)         Loads fpop from an extended precision variable.
  itof              Converts 16-bit integer to floating-point value in
  utof              Converts unsigned 16-bit value to floating point.
  ultof             Converts unsigned 32-bit value to floating point.
  ltof              Converts signed 32-bit value to floating point.
  fpadd             Adds fpop to fpacc.
  fpsub             Subtracts fpop from fpacc.
  fpcmp             Compares fpacc to fpop.
  fpmul             Multiplies fpacc by fpop.
  fpdiv             Divides fpacc by fpop.
  ftoa              Converts fpacc to a decimal string.
  etoa              Converts fpacc to ASCII string in exponent form.

Notes: Routines with the "2" suffix imply that the routine does not preserve the DI register. The routine returns DI pointing at the first character beyond the string. If the routine does not have the "2" suffix, then it preserves the ES:DI registers.

The "m" suffix implies that the routines automatically allocate storage for their string results on the heap by calling malloc. These routines return a pointer to the new string in ES:DI. Routines without the "m" suffix expect you to pass the address of a sufficiently large buffer in the ES:DI register pair.

Routines with the "I" suffix accept literal string constants in the code stream (that is, the string constant appears after the call to the specified routine).

If the routine you want isn't in the library, write it up, send it in, and we'll make sure it appears in the next release!

The library itself is currently divided into nine categories: input, output, file I/0, conversions, utilities, string operations, memory management, character-set operations, and floating-point operations. Most of these routines are high level; that is, they are nontrivial and typically require many lines of code and considerable knowledge to implement.

More Details.

The printf routine is a good example of a high-level routine. It's something C programmers take for granted, but you rarely see it in typical assembly language programs. A typical call to the printf routine is shown in Example 1. As you can see, this code is close to that used by C and much more convenient than the usual methods assembly language programmers employ. Except for the DB and DD directives, this probably doesn't look a whole lot like assembly language, though. The printf statement invokes a macro found in the distribution stdlib.a file. Among other things, this macro issues a call to the sl_printf subroutine in the library. I use macros to invoke the library routines, not because I'm trying to be cute, but as a way to provide "smart linking" facilities in MASM 5.1. See Listing One (page 80) for a sample macro definition from the library.

Example 1: A typical call to the UCR printf routine

  db      "The value of I is %3d, string s is %s\n",O
  dd      I, S

Not all routines in the UCR StdLib completely mimic their C counterparts. For example, itoa accepts an integer value in AX and converts it to a zero-terminated string of characters, storing the string starting at ES:DI. Like C, ES:DI must point at an array large enough to hold the result, or bad things may happen. However, it's often inconvenient to declare an array and load its address into ES:DI prior to calling itoa. Therefore, a second routine, itoam, is available to simplify the calling sequence. You pass itoam an integer value in AX and it returns a pointer to the converted string in ES:DI. You do not have to preallocate storage for the call; itoam does this automatically by calling malloc. At other times, it would be nice if itoa returned a pointer to the end of the converted string rather than to the beginning of it. (This is useful, for example, when building long strings via successive calls to routines such as itoa.) A third routine, itoa2, provides this facility. Having different routines such as itoa, itoa2, and itoam reduces the size of a program because you don't need as many "glue" instructions between library calls to massage the parameters.

The string routines should look familiar to C programmers. Almost all C string-handling routines (and then some!) are present in the UCR StdLib. Like itoa, there are various forms of some of the string functions, mainly for convenience. For example, strcat takes four different forms: strcat, strcatl, strcatm, and strcatml. These variants provide different ways of passing parameters to and from the strcat routine. strcat concatenates two strings: It copies the string pointed at by DX:SI to the end of the string pointed at by ES:DI. The destination string (ES:DI) must have sufficient memory allocated to hold the concatenation. strcatm also concatenates the string pointed at by ES:DI and DX:SI, but it does not treat the string pointed at by ES:DI as the target location. Instead, it (essentially) does what's shown in Example 2. strcatl links a literal string constant (the "I" suffix stands for "literal") to the end of the string referenced by ES:DI. Likewise, strcatml copies the source string (ES:DI) onto the heap, appends the literal string constant following the call, and returns the address of this new string in ES:DI. For example, if filename points at a DOS filename and you want to append ".EXE" to the end of it, you could use the code in Example 3.

Example 2: strcatm concatenates the string pointed at by ES:DI and DX:SI, but it does not treat the string pointed at by ES:DI as the target location.

  temp = malloc( strlen(es:di) + strlen(dx:si) +1);
  strcpy(temp, es:di);
  strcpy(temp + strlen(es:di), dx:si);
  es:di = temp;

Example 3: Use this code to append .EXE to the end of filename.

  les        di, filename
  db         ".EXE", 0
  mov        word ptr FullFileName, di
  mov        word ptr FullFileName+2, es

Listing Two (page 80) provides a flavor of UCR Stdlib routine use. This is a short program which computes various statistics about the information in a text file and prints the results. The distribution package also includes test.asm, a file that demonstrates use of each routine in the library. Hopefully, Listing One will show you that it's worthwhile to obtain a copy of the library, and the test file will exemplify the use of each routine in the library.


To keep the library growing, I assign my assembly language students at UC Riverside a final project of adding one new, useful routine to the library. My Commercial Software Development class gets charged with testing, documenting, and otherwise cleaning up the work of the assembly language students. As such, new routines appear in the library on a periodic basis. The text box entitled "Obtaining and Licensing the UCR Standard Library" provides details on obtaining the latest version of the library.

The UCR Standard Library has proven to be of considerable aid in getting students up to speed with 80x86 assembly language. Beginners are finding assembly language easier to deal with than ever before, particularly when combined with MASM 6.0's high-level constructs. Advanced assembly language programmers use the library to help them quickly develop new programs in record time. Given that the library is free for all to use, it is definitely worth adding to your personal development suite if you use or are interested in learning how to use 80x86 assembly language.

Obtaining and Licensing the UCR Standard Library

There are two "official" distribution points for the UCR StdLib distribution package: BIX and Internet. If you have access to the BIX telecommunications service, you may obtain a copy of "UCRSTDLB.ZIP" from the IBM.PC/LISTINGS area. If you have ftp access to the Internet, you may obtain a copy of UCRSTDLB.ZIP via anonymous ftp to After logging on, switch to the "PC" subdirectory (this is UNIX, so case counts!) and the rest should be fairly obvious.

In addition to the two official distribution points, the UCR StdLib routines are also available from many other telecommunications services, BBSs, and shareware distributors, including M&T Online and the DDJ Forum on CompuServe. However, there is a version control problem and I cannot guarantee that any service other than the ones mentioned above will have the latest version of the software. Given the way shareware and freeware software propagate around the world, I do not see a reasonable solution to this problem.

All replies and comments should be sent to the following address:

Randall Hyde
Department of Computer Science
UC Riverside, Riverside, CA 92521
Internet e-mail:
BIXmail: rhyde

by Randall Hyde

<a name="0086_000d">

Printf      macro
; The following extrn declaration only occurs if this is the first time
; printf appears in the source file.
        ifndef  sl_printf
stdlib      segment para public 'slcode'
        extrn   sl_printf:far
stdlib      ends
; Perform the call to the actual sl_printf routine:
        call    far ptr sl_printf

<a name="0086_000e">
<a name="0086_000f">
<a name="0086_000f">

; TS: A "Text Statistics" package which demonstrates the use of the UCR
;   Standard Library Package.
; Note: The purpose of this program is not to demonstrate blazing fast
;   assembly code (it's not particularly fast) but rather to demonstrate how
;   easy it is to write assembly code using the standard library and MASM 6.0.
; Randall Hyde
;  The following include must be outside any segment and before the
;  ZZZZZZSEG segment.  It includes all the macro definitions for the
;  UCR Standard Library.
        include     stdlib.a    ;Links into the UCR Standard
        includelib  stdlib.lib  ; Library package.
dseg        segment para public 'data'
WordCount   dw  0       ;Holds file word count value
LineCnt     dw  0       ;Holds # of lines in file
ControlCnt  dw  0       ;Counts # of control characters
Punct       dw      0       ;Counts # of punctuation characters
AlphaCnt    dw  0       ;Counts # of alphabetic characters
NumericCnt  dw  0       ;Counts numeric digits in file
Other       dw  0       ;Counts other chars in file
MemorySize  dw  0       ;# of paragraphs of free memory
Chars       dw  0       ;Total number of chars in file
TotalChars  dq  0.0     ;FP version of the above
FileHandle  dw  0       ;STDLIB file handle
Const100    dq  100.0
; Create some sets to use in this program:
        set CharSet,Alphabetic,Punctuation,Control
; Character Counter array.  CharCnt [ch] contains the number of "ch"
; characters appearing in the file.
CharCnt     dw  256 dup (0)
; Boolean flag to denote in/not in a word:
InWord      db  0
dseg        ends
cseg        segment para public 'code'
        assume  cs:cseg, ds:dseg
; LESI is a macro which loads a 32-bit immediate value into ES:DI.
lesi        macro   adrs
        mov     di, seg adrs
        mov es, di
        lea di, adrs
; ldxi loads a 32-bit immediate value into dx:si:
ldxi        macro   adrs
        mov     dx, seg adrs
        lea si, adrs
; Some useful constants-
cr      equ 13
lf      equ 10
EOFError    equ 8
        public  PSP     ;DOS Program Segment Prefix
PSP     dw  ?       ;Needed by StdLib MemInit routine
; Okay, here's the main program which does the job:
TS      proc
        mov cs:PSP, es      ;Save pgm seg prefix
        mov ax, seg dseg        ;Set up the segment registers
        mov ds, ax
        mov es, ax
; Initialize the memory manager, giving all free memory to the heap.
        mov dx, 0
        mov MemorySize, cx  ;Save # of available paragraphs.
; Set up the character sets:
;  First, build the Alphabetic set:
        mov al, "A"
        mov ah, "Z"
        lesi    Alphabetic
        db  "abcdefghijklmnopqrstuvwxyz",0
; Create the set with the punctuation characters:
        lesi    Punctuation
        db  "!@#$%^&*()_-+={[}]|\':;<,>.?/~`", '"', 0
; Create the control character set:
        lesi    Control
        mov al,0
        mov ah, 1fh
        mov al, 7fh
; Print the amount of available memory and prompt the user to enter a file name.
        db  "Text Statistics Program",cr,lf
        db  "There are %d paragraphs of memory available",cr,lf
        db  lf
        db  "Enter a filename:",0
        dd  MemorySize
        getsm               ;Get the filename.
; Open the file.
        mov al, 0           ;Open for reading.
        fopen               ;Open the file.
        jnc GoodOpen
; If the carry flag comes back set, we've got an error, print an appropriate
; message and quit:
        db  "DOS error #",0
        puti                ;Error code is in AX.
        jmp Return2DOS
; If the carry flag comes back clear, we've successfully opened the file. AX
; contains the STDLIB filehandle, ES:DI still points at the filename
; allocated on the heap:
GoodOpen:   mov FileHandle, AX      ;Save STDLIB file handle.
        db  "Computing text statistics for ",0
        puts                ;Print filename
        free                ;Dispose of space on heap
; The following loops check for transitions between words and delimiters. Each
; time we go from "not a word" -> "word" this code bumps up word count by one.
        mov ax, FileHandle
TSLoop:     getc
        jnc NoError
        jmp ReadError
; See if the character is alphabetic
NoError:    lesi    Alphabetic      ;Set contains A-Z, a-z
        jz  NotAlphabetic
        inc AlphaCnt
        jmp StatDone
; See if the character is a digit:
NotAlphabetic:  cmp al, "0"
        jb  NotNumeric
        cmp al, "9"
        ja  NotNumeric
        inc NumericCnt
        jmp StatDone
; See if the character is a punctuation character
NotNumeric: lesi    Punctuation
        jz  NotPunctuation
        inc Punct
        jmp StatDone
; See if this is a control character:
NotPunctuation: lesi    Control
        jz  NotControl
        inc ControlCnt
        jmp StatDone
NotControl: inc Other
StatDone:       mov bl, al      ;Use char as index into CharCnt
        mov bh, 0
        shl bx, 1       ;Convert word index to byte index
        inc CharCnt [bx]
; Count lines and characters here:
        cmp al, lf
        jne NotNewLine
        inc LineCnt
NotNewLine:     inc Chars
; Count words down here
        cmp InWord, 0       ;See if we're in a word.
        je  NotInAWord
        cmp al, " "
        ja  WCDone
        mov InWord, 0       ;Just left a word
        jmp WCDone
NotInAWord: cmp al, " "
        jbe WCDone
        mov InWord, 1       ;Just entered a word
        inc WordCount
; Okay, or the current character into the character set so we can keep
; track of the characters which appear in this file.
        lesi    CharSet
        jmp TSLoop
; Come down here on EOF or other read error.
ReadError:  cmp ax, EOFError
        je  Quit
        db  "DOS Error ",0
        jmp Return2DOS
; Return to DOS.
Quit:       freadoff
        mov ax, FileHandle
        db  cr,lf,lf
        db  "Number of words in this file is %d",cr,lf
        db  "Number of lines in this file is %d",cr,lf
        db  "Number of control characters is %d",cr,lf
        db  "Number of punctuation characters is %d",cr,lf
        db  "Number of alphabetic characters is %d",cr,lf
        db  "Number of numeric characters is %d",cr,lf
        db  "Number of other characters is %d",cr,lf
        db  "Total number of characters is %d",cr,lf
        db  lf, 0
        dd  WordCount,LineCnt,ControlCnt,Punct
        dd  AlphaCnt,NumericCnt,Other,Chars
; Print the characters that actually appeared in the file.
        lesi    CharSet
EC64:       mov cx, 64          ;Chars/line on output.
EachChar:   RmvItem
        cmp al, 0
        je  CSDone
        cmp al, " "
        jbe EachChar
        loop    EachChar
        jmp EC64
CSDone:     print
        db  cr,lf,lf
        db  "Press any key to continue:",0
; Now print the statistics for each character:
        mov ax, Chars       ;Get character count,
        utof                ; convert it to a floating
        lesi    TotalChars      ; point value, and save this
        sdfpa               ; value in "TotalChars".
; Print out each character, the number of occurrences, and the ratio of
; this character's count to the total number of characters.
        mov bx, " "*2       ;Start output with spaces.
ComputeRatios:  cmp CharCnt[bx], 0
        je  SkipThisChar
        mov ax, bx
        shr ax, 1           ;Convert index to character
        putc                ; and print it.
        db  " = ",0
        mov ax, CharCnt [bx]
        mov cx, 4
        db  "  Percentage of total is ",0
; Divide by the total number of characters in the file:
        lesi    TotalChars
; Multiply by 100 to get a percentage
        lesi    Const100
; Print the ratio:
        mov al, 7
        mov ah, 3
        db  "%",cr,lf,0
SkipThisChar:   inc bx
        inc bx
        cmp bx, 200h
        jb      ComputeRatios
Return2DOS: mov     ah, 4ch
        int     21h
TS      endp
cseg            ends
; Allocate a reasonable amount of space for the stack (2k).
sseg        segment para stack 'stack'
stk     db  256 dup ("stack   ")
sseg        ends
; zzzzzzseg must be the last segment that gets loaded into memory!
; The UCR Standard Library package uses this segment to determine where
; the end of the program lies.
zzzzzzseg   segment para public 'zzzzzz'
LastBytes   db  16 dup (?)
zzzzzzseg   ends
        end TS

Copyright © 1992, Dr. Dobb's Journal

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