Assembly language program codes

A "static library" is really nothing more than a collection of probably related object files. This document does not cover how to use all the different assemblers; you need to read the documentation that comes with them. We will, however, give step-by-step instructions and complete examples of all three of these assemblers for a few extremely simple programs.

Some linkers out there include. In our first example we will use system calls for writing to a file call number 1 and exiting a process call number Here it is in the NASM assembly language:.

If you just enter " gcc hello. You can suppress the link step with the -c option to gcc , or do the assembly and linking in one step by telling the linker not to use the C library with -nostdlib. System Calls in bit Linux There are some systems with bit builds of Linux out there still.

Although it might be interesting to show some examples for historical reasons, this introduction is probably better kept short. Sometimes you might like to use your favorite C library functions in your assembly code. This should be trivial because the C library functions are all stored in a C library, such as libc. Technically the code is probably in a dynamic library, like libc. Still, all we have to do is place calls to C functions in our assembly language program, and link with the static C library and we are set.

So if we link with a C library, all we have to do is define main and end with a ret instruction! Here is a simple example in NASM, which illustrates calling puts. To assemble and run: ; ; nasm -fmacho64 hola. Yes No. Not Helpful 13 Helpful 2. Include your email address to get a message when this question is answered. Writing effective code in assembly language or any other generally requires somewhat significant study. You'll especially want to learn the required syntax for assembly language statements and how to compile and link an assembly program.

Helpful 3 Not Helpful 0. If you experience any difficulties when attempting to set up a specific assembler, it may be wise to join a forum in which particular questions may be addressed. Helpful 1 Not Helpful 0. This is a good way to start. Helpful 1 Not Helpful 1. Submit a Tip All tip submissions are carefully reviewed before being published. You Might Also Like How to. How to. About This Article. Co-authored by:. Co-authors: Updated: February 8, Categories: Programming.

In other languages Deutsch: In Assembly programmieren lernen. Nederlands: Programmeren in Assembly. Thanks to all authors for creating a page that has been read , times. Is this article up to date? Cookies make wikiHow better. By continuing to use our site, you agree to our cookie policy. Featured Articles How to. Input and output are usually in the measurement of milliseconds, compared with register and memory in nanoseconds or microseconds.

To be more efficient, trying to reduce system API calls is a nice consideration. For details about the Win32 functions mentioned in the following, please refer to MSDN to understand. An example is to output 20 lines of 50 random characters with random colors as below:.

Simply set its color by. When write 50 characters, make a new line. So we can create a nested iteration, the outer loop for 20 rows and the inner loop for 50 columns. As 50 by 20 , we call these two console output functions times. However, another pair of API functions can be more efficient, by writing 50 characters in a row and setting their colors once a time. Now we can write the 50 random characters per line with two calls here:.

Totally we only call these two APIs 20 times. The following is the PTR specification:. Let's discuss how to use them. As an integer type takes four bytes, it makes a pointer type cast from the array name fourBytes , a char address, to an unsigned int address.

Then it displays the integer result by dereferencing the unsigned int pointer. As expected in x86 Intel based system, this verifies the little endian by showing in hexadecimal. Then in the following data segment, the address variable dwPtr takes over the fourBytes memory. To define a procedure with a parameter list, you might want to use PTR in both ways.

The data ranges, for example of 8-bit, are. Based on the hardware point of view, all CPU instructions operate exactly the same on signed and unsigned integers, because the CPU cannot distinguish between signed and unsigned.

For example, when define. Both of them have the 8-bit binary FFh saved in memory or moved to a register. You, as a programmer, are solely responsible for using the correct data type with an instruction and are able to explain a results from the flags affected:.

Certainly is bigger than 1 , so that makes it jump to L1. An unsigned comparison is determined by CF and the zero flag ZF as shown in the following examples:. Only difference is JG here instead of JA. Certainly -1 is smaller than 1 , so that makes JMP to L2. A signed comparison is determined by OF and the sign flag SF as shown in the following examples:.

For a positive integer, if its highest bit sign bit is zero, there is no difference to manually clear the upper part of a dividend or mistakenly use a sign extension as shown in the following example:.

So if your value is positive and its highest bit is zero, using CDQ and. But, if you make this. Try above in debug to see how integer division overflow happens as a result.

If really want to make it correct as unsigned DIV , you must:. On the other side, if really want to use CBW , it means that you perform a signed division. Then you must use IDIV :. As seen here, 81h in signed byte is decimal so that signed IDIV gives the correct quotient and remainder as above.

To talk about the carry flag CF , let's take the following two arithmetic calculations:. From a human being's point of view, they do exactly the same operation, minus 1 with the result FEh.

Likewise, based on the hardware point, for either calculation, the CPU does the same operation by representing -1 as a two's complement FFh and then add it to Now is FFh and the binary format of -1 is also FFh. This is how it has been calculated:. A CPU operates exactly the same on signed and unsigned because it cannot distinguish them. A programmer should be able to explain the behavior by the flag affected.

Since we talk about the CF , it means we consider two calculations as unsigned. The key information is that -1 is FFh and then in decimal. So the logic interpretation of CF is. Now let's see the overflow flag OF , still with above two arithmetic calculations as this:. We can have two ways to determine OF , the logic rule and hardware implementation.

For signed, is -1 FFh. Our two examples just do -1 plus -1 with the result The following is the specification from MSDN :. LOCAL localname [[, localname]] LOCAL label [[ [count ] ]] [[:type]] [[, label [[ [count] ]] [[type]]]] This specification is not clear enough to understand.

In this section, I'll expose the essential difference in between and show two example using the LOCAL directive, one in a procedure and the other in a macro. As for your familiarity, both examples calculate the nth Fibonacci number as early FibonacciByMemory. The main point delivered here is:. For the basic concepts and implementations of data segment and stack frame , please take a look at some textbook or MASM manual that could be worthy of several chapters without being talked here.

The following is a procedure with a parameter n to calculate nth Fibonacci number returned in EAX. I let the loop counter ECX take over the parameter n. Please compare it with FibonacciByMemory. The logic is the same with only difference of using the local variables pre and cur here, instead of global variables previous and current in FibonacciByMemory.

The following is the code generated from the VS Disassembly window at runtime. As you can see, each line of assembly source is translated into machine code with the parameter n and two local variables created on the stack frame, referenced by EBP :.

Also without a stack frame, I have to create global variables mPre and mCur on the data segment. The mFibonacciByMacro can be like this:. Nothing changed from the original code with just a substitution of The variables mPre and mCur are visible explicitly.

Now let's call it twice, like. This is still fine for the first mFibonacciByMacro 12 but secondly, causes three redefinitions in preprocessing mFibonacciByMacro Not only are data labels, i.

This is because in assembly code, each label is actually a memory address and the second label of any mPre , mCur , or mL should take another memory, rather than defining an already created one:.

What remains is to put the rules to use by constructing a working program, to take the theory into the field and show how machine language is done. Continually strives to remain the largest and most complete source for related information in the world. NMOS Opcodes. Instruction Set. Addressing Modes. Instruction Reference. Stella Programmer's Guide. Cycle counting is an important aspect of Atari programming.

It makes possible the positioning of sprites, the drawing of six-digit scores, non-mirrored playfield graphics and many other cool TIA tricks that keep every game from looking like Combat. Atari programming is different from any other kind of programming in many ways. Just one of these ways is the flow of the program. The "bankswitching bible.

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