2.10 Introduction to the HLA Standard Library
There are two reasons HLA is much easier to learn and use than standard assembly language. The first reason is HLA's high level syntax for declarations and control structures. This HLA feature leverages your high level language knowledge, reducing the need to learn arcane syntax, allowing you to learn assembly language more efficiently. The other half of the equation is the HLA Standard Library. The HLA Standard Library provides lot of commonly needed, easy to use, assembly language routines that you can call without having to write this code yourself (or even learn how to write yourself). This eliminates one of the larger stumbling blocks many people have when learning assembly language: the need for sophisticated I/O and support code in order to write basic statements. Prior to the advent of a standardized assembly language library, it often took weeks of study before a new assembly language programmer could do as much as print a string to the display. With the HLA Standard Library, this roadblock is removed and you can concentrate on learning assembly language concepts rather than learning low-level I/O details that are specific to a given operating system.
A wide variety of library routines is only part of HLA's support. After all, assembly language libraries have been around for quite some time1. HLA's Standard Library continues the HLA tradition by providing a high level language interface to these routines. Indeed, the HLA language itself was originally designed specifically to allow the creation of a high-level accessible set of library routines2. This high level interface, combined with the high level nature of many of the routines in the library, packs a surprising amount of power in an easy to use package.
The HLA Standard Library consists of several modules organized by category. The following table lists many of the modules that are available3:
Table 3: HLA Standard Library Modules Name Description args Command line parameter parsing support routines. conv Various conversions between strings and other values. cset Character set functions. DateTime Calendar, date, and time functions. excepts Exception handling routines. fileio File input and output routines hla Special HLA constants and other values. Linux Linux system calls (HLA Linux version only). math Transcendental and other mathematical functions. memory Memory allocation, deallocation, and support code. misctypes Miscellaneous data types. patterns The HLA pattern matching library. rand Pseudo-random number generators and support code. stdin User input routines stdout Provides user output and several other support routines. stdlib A special include file that links in all HLA standard library modules. strings HLA's powerful string library. tables Table (associative array) support routines. win32 Constants used in Windows calls (HLA Win32 version, only) x86 Constants and other items specific to the 80x86 CPU.
Later sections of this text will explain many of these modules in greater detail. This section will concentrate on the most important routines (at least to beginning HLA programmers), the stdio library.
2.10.1 Predefined Constants in the STDIO Module
Perhaps the first place to start is with a description of some common constants that the STDIO module defines for you. One constant you've seen already in code appearing in this chapter. Consider the following (typical) example:stdout.put( "Hello World", nl );
The nl appearing at the end of this statement stands for newline. The nl identifier is not a special HLA reserved word, nor is it specific to the stdout.put statement. Instead, it's simply a predefined constant that corresponds to the string containing the standard end of line sequence (this is a carriage return/line feed pair under Windows or just a line feed under Linux).
In addition to the nl constant, the HLA standard I/O library module defines several other useful character constants. They are
- stdio.bell The ASCII bell character. Beeps the speaker when printed.
- stdio.bs The ASCII backspace character.
- stdio.tab The ASCII tab character.
- stdio.eoln A linefeed character (even under Windows).
- stdio.lf The ASCII linefeed character.
- stdio.cr The ASCII carriage return character.
Except for nl, these characters appear in the stdio namespace (and, therefore, require the "stdio." prefix). The placement of these ASCII constants within the stdio namespace is to help avoid naming conflicts with your own variables. The nl name does not appear within a namespace because you will use it very often and typing stdio.nl would get tiresome very quickly.
2.10.2 Standard In and Standard Out
Many of the HLA I/O routines have a stdin or stdout prefix. Technically, this means that the standard library defines these names in a namespace4. In practice, this prefix suggests where the input is coming from (the standard input device) or going to (the standard output device). By default, the standard input device is the system keyboard. Likewise, the default standard output device is the console display. So, in general, statements that have stdin or stdout prefixes will read and write data on the console device.
When you run a program from the command line window (or shell), you have the option of redirecting the standard input and/or standard output devices. A command line parameter of the form ">outfile" redirects the standard output device to the specified file (outfile). A command line parameter of the form "<infile" redirects the standard input so that its data comes from the specified input file (infile). The following examples demonstrate how to use these parameters when running a program named "testpgm" in the command window5:testpgm <input.data testpgm >output.txt testpgm <in.txt >output.txt
2.10.3 The stdout.newln Routine
The stdout.newln procedure prints a newline sequence to the standard output device. This is functionally equivalent to saying "stdout.put( nl );" Of course, the call to stdout.newln is sometimes a little more convenient. Example of call:stdout.newln();
2.10.4 The stdout.putiX Routines
The stdout.puti8, stdout.puti16, and stdout.puti32 library routines print a single parameter (one byte, two bytes, or four bytes, respectively) as a signed integer value. The parameter may be a constant, a register, or a memory variable, as long as the size of the actual parameter is the same as the size of the formal parameter.
These routines print the value of their specified parameter to the standard output device. These routines will print the value using the minimum number of print positions possible. If the number is negative, these routines will print a leading minus sign. Here are some examples of calls to these routines:stdout.puti8( 123 ); stdout.puti16( DX ); stdout.puti32( i32Var );
2.10.5 The stdout.putiXSize Routines
The stdout.puti8Size, stdout.puti16Size, and stdout.puti32Size routines output signed integer values to the standard output, just like the stdout.putiX routines. These routines, however, provide more control over the output; they let you specify the (minimum) number of print positions the value will require on output. These routines also let you specify a padding character should the print field be larger than the minimum needed to display the value. These routines require the following parameters:stdout.puti8Size( Value8, width, padchar ); stdout.puti16Size( Value16,width, padchar ); stdout.puti32Size( Value32, width, padchar );
The ValueX parameter can be a constant, a register, or a memory location of the specified size. The width parameter can be any signed integer constant that is between -256 and +256; this parameter may be a constant, register (32-bit), or memory location (32-bit). The padchar parameter should be a single character value.
Like the stdout.putiX routines, these routines print the specified value as a signed integer constant to the standard output device. These routines, however, let you specify the field width for the value. The field width is the minimum number of print positions these routines will use when printing the value. The width parameter specifies the minimum field width. If the number would require more print positions (e.g., if you attempt to print "1234" with a field width of two), then these routines will print however many characters are necessary to properly display the value. On the other hand, if the width parameter is greater than the number of character positions required to display the value, then these routines will print some extra padding characters to ensure that the output has at least width character positions. If the width value is negative, the number is left justified in the print field; if the width value is positive, the number is right justified in the print field.
If the absolute value of the width parameter is greater than the minimum number of print positions, then these stdout.putiXSize routines will print a padding character before or after the number. The padchar parameter specifies which character these routines will print. Most of the time you would specify a space as the pad character; for special cases, you might specify some other character. Remember, the padchar parameter is a character value; in HLA character constants are surrounded by apostrophes, not quotation marks. You may also specify an eight-bit register as this parameter.
Here is a short HLA program that demonstrates the use of the puti32Size routine to display a list of values in tabular form:program NumsInColumns; #include( "stdlib.hhf" ); var i32: int32; ColCnt: int8; begin NumsInColumns; mov( 96, i32 ); mov( 0, ColCnt ); while( i32 > 0 ) do if( ColCnt = 8 ) then stdout.newln(); mov( 0, ColCnt ); endif; stdout.puti32Size( i32, 5, ` ` ); sub( 1, i32 ); add( 1, ColCnt ); endwhile; stdout.newln(); end NumsInColumns; Program 2.4 Columnar Output Demonstration Using stdio.Puti32Size
2.10.6 The stdout.put Routine
The stdout.put routine6 is one of the most flexible output routines in the standard output library module. It combines most of the other output routines into a single, easy to use, procedure.
The generic form for the stdout.put routine is the following:stdout.put( list_of_values_to_output );
The stdout.put parameter list consists of one or more constants, registers, or memory variables, each separated by a comma. This routine displays the value associated with each parameter appearing in the list. Since we've already been using this routine throughout this chapter, you've already seen lots of examples of this routine's basic form. It is worth pointing out that this routine has several additional features not apparent in the examples appearing in this chapter. In particular, each parameter can take one of the following two forms:
The value may be any legal constant, register, or memory variable object. In this chapter, you've seen string constants and memory variables appearing in the stdout.put parameter list. These parameters correspond to the first form above. The second parameter form above lets you specify a minimum field width, similar to the stdout.putiXSize routines7. The following sample program produces the same output as the previous program; however, it uses stdout.put rather than stdout.puti32Size:program NumsInColumns2; #include( "stdlib.hhf" ); var i32: int32; ColCnt: int8; begin NumsInColumns2; mov( 96, i32 ); mov( 0, ColCnt ); while( i32 > 0 ) do if( ColCnt = 8 ) then stdout.newln(); mov( 0, ColCnt ); endif; stdout.put( i32:5 ); sub( 1, i32 ); add( 1, ColCnt ); endwhile; stdout.put( nl ); end NumsInColumns2; Program 2.5 Demonstration of stdout.put Field Width Specification
The stdout.put routine is capable of much more than the few attributes this section describes. This text will introduce those additional capabilities as appropriate.
2.10.7 The stdin.getc Routine.
The stdin.getc routine reads the next available character from the standard input device's input buffer8. It returns this character in the CPU's AL register. The following example program demonstrates a simple use of this routine:program charInput; #include( "stdlib.hhf" ); var counter: int32; begin charInput; // The following repeats as long as the user // confirms the repetition. repeat // Print out 14 values. mov( 14, counter ); while( counter > 0 ) do stdout.put( counter:3 ); sub( 1, counter ); endwhile; // Wait until the user enters `y' or `n'. stdout.put( nl, nl, "Do you wish to see it again? (y/n):" ); forever stdin.readLn(); stdin.getc(); breakif( al = `n' ); breakif( al = `y' ); stdout.put( "Error, please enter only `y' or `n': " ); endfor; stdout.newln(); until( al = `n' ); end charInput; Program 2.6 Demonstration of the stdin.getc() Routine
This program uses the stdin.ReadLn routine to force a new line of input from the user. A description of stdin.ReadLn appears just a little later in this chapter.
2.10.8 The stdin.getiX Routines
The stdin.geti8, stdin.geti16, and stdin.geti32 routines read eight, 16, and 32-bit signed integer values from the standard input device. These routines return their values in the AL, AX, or EAX register, respectively. They provide the standard mechanism for reading signed integer values from the user in HLA.
Like the stdin.getc routine, these routines read a sequence of characters from the standard input buffer. They begin by skipping over any white space characters (spaces, tabs, etc.) and then convert the following stream of decimal digits (with an optional, leading, minus sign) into the corresponding integer. These routines raise an exception (that you can trap with the TRY..ENDTRY statement) if the input sequence is not a valid integer string or if the user input is too large to fit in the specified integer size. Note that values read by stdin.geti8 must be in the range -128..+127; values read by stdin.geti16 must be in the range -32,768..+32,767; and values read by stdin.geti32 must be in the range -2,147,483,648..+2,147,483,647.
The following sample program demonstrates the use of these routines:program intInput; #include( "stdlib.hhf" ); var i8: int8; i16: int16; i32: int32; begin intInput; // Read integers of varying sizes from the user: stdout.put( "Enter a small integer between -128 and +127: " ); stdin.geti8(); mov( al, i8 ); stdout.put( "Enter a small integer between -32768 and +32767: " ); stdin.geti16(); mov( ax, i16 ); stdout.put( "Enter an integer between +/- 2 billion: " ); stdin.geti32(); mov( eax, i32 ); // Display the input values. stdout.put ( nl, "Here are the numbers you entered:", nl, nl, "Eight-bit integer: ", i8:12, nl, "16-bit integer: ", i16:12, nl, "32-bit integer: ", i32:12, nl ); end intInput; Program 2.7 stdin.getiX Example Code
You should compile and run this program and test what happens when you enter a value that is out of range or enter an illegal string of characters.
2.10.9 The stdin.readLn and stdin.flushInput Routines
Whenever you call an input routine like stdin.getc or stdin.geti32, the program does not necessarily read the value from the user at that moment. Instead, the HLA Standard Library buffers the input by reading a whole line of text from the user. Calls to input routines will fetch data from this input buffer until the buffer is empty. While this buffering scheme is efficient and convenient, sometimes it can be confusing. Consider the following code sequence:stdout.put( "Enter a small integer between -128 and +127: " ); stdin.geti8(); mov( al, i8 ); stdout.put( "Enter a small integer between -32768 and +32767: " ); stdin.geti16(); mov( ax, i16 );
Intuitively, you would expect the program to print the first prompt message, wait for user input, print the second prompt message, and wait for the second user input. However, this isn't exactly what happens. For example if you run this code (from the sample program in the previous section) and enter the text "123 456" in response to the first prompt, the program will not stop for additional user input at the second prompt. Instead, it will read the second integer (456) from the input buffer read during the execution of the stdin.geti8 call.
In general, the stdin routines only read text from the user when the input buffer is empty. As long as the input buffer contains additional characters, the input routines will attempt to read their data from the buffer. You may take advantage of this behavior by writing code sequences such as the following:stdout.put( "Enter two integer values: " ); stdin.geti32(); mov( eax, intval ); stdin.geti32(); mov( eax, AnotherIntVal );
This sequence allows the user to enter both values on the same line (separated by one or more white space characters) thus preserving space on the screen. So the input buffer behavior is desirable every now and then.
Unfortunately, the buffered behavior of the input routines is definitely counter-intuitive at other times. Fortunately, the HLA Standard Library provides two routines, stdin.readLn and stdin.flushInput, that let you control the standard input buffer. The stdin.readLn routine discards everything that is in the input buffer and immediately requires the user to enter a new line of text. The stdin.flushInput routine simply discards everything that is in the buffer. The next time an input routine executes, the system will require a new line of input from the user. You would typically call stdin.readLn immediately before some standard input routine; you would normally call stdin.flushInput immediately after a call to a standard input routine.
Note: If you are calling stdin.readLn and you find that you are having to input your data twice, this is a good indication that you should be calling stdin.flushInput rather than stdin.readLn. In general, you should always be able to call stdin.flushInput to flush the input buffer and read a new line of data on the next input call. The stdin.readLn routine is rarely necessary, so you should use stdin.flushInput unless you really need to immediately force the input of a new line of text.
2.10.10 The stdin.get Macro
The stdin.get macro combines many of the standard input routines into a single call, in much the same way that stdout.put combines all of the output routines into a single call. Actually, stdin.get is much easier to use than stdout.put since the only parameters to this routine are a list of variable names.
Let's rewrite the example given in the previous section:stdout.put( "Enter two integer values: " ); stdin.geti32(); mov( eax, intval ); stdin.geti32(); mov( eax, AnotherIntVal );
Using the stdin.get macro, we could rewrite this code as:stdout.put( "Enter two integer values: " ); stdin.get( intval, AnotherIntVal );
As you can see, the stdin.get routine is a little more convenient to use.
Note that stdin.get stores the input values directly into the memory variables you specify in the parameter list; it does not return the values in a register unless you actually specify a register as a parameter. The stdin.get parameters must all be variables or registers9.
2.11 Putting It All Together
This chapter has covered a lot of ground! While you've still got a lot to learn about assembly language programming, this chapter, combined with your knowledge of high level languages, provides just enough information to let you start writing real assembly language programs.
In this chapter, you've seen the basic format for an HLA program. You've seen how to declare integer, character, and boolean variables. You have taken a look at the internal organization of the Intel 80x86 CPU family and learned about the MOV, ADD, and SUB instructions. You've looked at the basic HLA high level language control structures (IF, WHILE, REPEAT, FOR, BREAK, BREAKIF, FOREVER, and TRY) as well as what constitutes a legal boolean expression in these statements. Finally, this chapter has introduced several commonly-used routines in the HLA Standard Library.
You might think that knowing only three machine instructions is hardly sufficient to write meaningful programs. However, those three instructions (mov, add, and sub), combined with the HLA high level control structures and the HLA Standard Library routines are actually equivalent to knowing several dozen machine instructions. Certainly enough to write simple programs. Indeed, with only a few more arithmetic instructions plus the ability to write your own procedures, you'll be able to write almost any program. Of course, your journey into the world of assembly language has only just begun; you'll learn some more instructions, and how to use them, starting in the next chapter.
1E.g., the UCR Standard Library for 80x86 Assembly Language Programmers.
2HLA was created because MASM was insufficient to support the creation of the UCR StdLib v2.0.
3Since the HLA Standard Library is expanding, this list is probably out of date. Please see the HLA documentation for a current list of Standard Library modules.
4Namespaces will be the subject of a later chapter.
5Note for Linux users: depending on how your system is set up, you may need to type "./" in front of the program's name to actually execute the program, e.g., "./testpgm <input.data".
6Stdout.put is actually a macro, not a procedure. The distinction between the two is beyond the scope of this chapter. However, this text will describe their differences a little later.
7Note that you cannot specify a padding character when using the stdout.put routine; the padding character defaults to the space character. If you need to use a different padding character, call the stdout.putiXSize routines.
8"Buffer" is just a fancy term for an array.
9Note that register input is always in hexadecimal or base 16. The next chapter will discuss hexadecimal numbers.