Why aren t programs written in Assembly more often

Question

It seems to be a mainstream opinion that assembly programming takes longer and is more difficult to program in than a higher level language such as C  Therefore it seems to be recommend or assumed that it is better to write in a higher level language for these reasons and for the reason of better portability   Recently I ve been writing in x86 assembly and it has dawned on me that perhaps these reasons are not really true  except perhaps portability  Perhaps it is more of a matter of familiarity and knowing how to write assembly well  I also noticed that programming in assembly is quite different than programming in an HLL  Perhaps a good and experienced assembly programmer could write programs just as easily and as quickly as an experienced C programmer writing in C   Perhaps it is because assembly programming is quite different than HLLs  and so requires different thinking  methods and ways  which makes it seem very awkward to program in for the unfamiliar  and so gives it its bad name for writing programs in   If portability isn t an issue  then really  what would C have over a good assembler such as NASM   Edit  Just to point out  When you are writing in assembly  you don t have to write just in instruction codes  You can use macros and procedures and your own conventions to make various abstractions to make programs more modular  more maintainable and easier to read  This is where being familiar with how to write good assembly comes in

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Why  Simple   Compare this            for  var i   1  i  lt   100  i                          if  i   3    0                  Console Write  Fizz                if  i   5    0                  Console Write  Buzz                if  i   3    0  amp  amp  i   5    0                  Console Write i               Console WriteLine                with   locals init        0  int32 i  L 0000  ldc i4 1  L 0001  stloc 0  L 0002  br s L 003b L 0004  ldloc 0  L 0005  ldc i4 3  L 0006  rem  L 0007  brtrue s L 0013 L 0009  ldstr  Fizz  L 000e  call void  mscorlib System Console  Write string  L 0013  ldloc 0  L 0014  ldc i4 5  L 0015  rem  L 0016  brtrue s L 0022 L 0018  ldstr  Buzz  L 001d  call void  mscorlib System Console  Write string  L 0022  ldloc 0  L 0023  ldc i4 3  L 0024  rem  L 0025  brfalse s L 0032 L 0027  ldloc 0  L 0028  ldc i4 5  L 0029  rem  L 002a  brfalse s L 0032 L 002c  ldloc 0  L 002d  call void  mscorlib System Console  Write int32  L 0032  call void  mscorlib System Console  WriteLine   L 0037  ldloc 0  L 0038  ldc i4 1  L 0039  add  L 003a  stloc 0  L 003b  ldloc 0  L 003c  ldc i4 s 100 L 003e  ble s L 0004 L 0040  ret    They re identical feature-wise  The second one isn t even assembler but  NET IL  Intermediary Language  similar to Java s bytecode   The second compilation transforms the IL into native code  i e  almost assembler   making it even more cryptical

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I ve been programming in assembly now for about a month   I often write a piece of code in C and then compile it to assembly to assist me   Perhaps I am not utilizing the full optimizing power of the C compiler but it appears that my C asm source is including unnecessary operations   So I am beginning to see that the talk of a good C compiler outperforming a good assembly coder is not always true   Anyways  my assembly programs are so fast   And the more I use assembly the less time it takes me to write out my code because it s really not that hard   Also the comment about assembly having poor legibility is not true   If you label your programs correctly and make comments when there is additional elaboration needed you should be all set   In fact in ways assembly is more clear to the programmer because they are seeing what is happening at the level of the processor   I don t know about other programmers but for me I like knowing what s happening  rather than things being in a sort of black box   With that said the real advantage of compilers is that a compiler can understand patterns and relationships and then automatically code them in the appropriate locations in the source   One popular example are virtual functions in C   which requires the compiler to optimally map function pointers   However a compiler is limited to doing what the maker of the compiler allows the compiler to do   This leads to programmers sometimes having to resort to doing bizarre things with their code   adding coding time  when they could have been done trivially with assembly     Personally I think the marketplace heavily supports high level languages   If assembly language was the only language in existence today then their would be about 70  less people programming and who knows where our world would be  probably back in the 90 s   Higher level languages appeal to a broader range of people   This allows a higher supply of programmers to build the needed infrastructure of our world   Developing nations like China and India benefit heavily from languages like Java   These countries will fast develop their IT infrastructure and people will become more interconnected     So my point is that high level languages are popular not because they produce superior code but because they help to meet demand in the world s marketplaces

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One of the early discoveries  you ll find it in Brooks  Mythical Man-Month  which is from experience in the 1960s  was that people were more or less as productive in one language as another  in debugged lines of code per day   This obviously isn t universally true  and can breaks when pushed too far  but it was generally true of the high-level languages of Brooks  time   Therefore  the fastest way to get productivity would be to use languages where one individual line of code did more  and indeed this works  at least for languages of complexity like FORTRAN and COBOL  or to give a more modern example C

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ASM has poor legibility and isn t really maintainable compared to higher-level languages   Also  there are many fewer ASM developers than for other more popular languages  such as C   Furthermore  if you use a higher-level language and new ASM instructions become available  SSE for example   you just need to update your compiler and your old code can easily make use of the new instructions   What if the next CPU has twice as many registers   The converse of this question would be  What functionality do compilers provide   I doubt you can want to should optimize your ASM better than gcc -O3 can

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There was a vicious cycle as assembly became less commonplace  as higher level languages matured  assembly language instruction sets were built less for programmer convenience and more for the convenience of compilers   So now  realistically  it may be very hard to make the right decisions on  say  which registers you should use or which instructions are slightly more efficient  Compilers can use heuristics to figure out which tradeoffs are likely to have the best payoff  We can probably think through smaller problems and find local optimizations that might beat our now pretty sophisticated compilers  but odds are that in the average case  a good compiler will do a better job on the first try than a good programmer probably will  Eventually  like John Henry  we might beat the machine  but we might seriously burn ourselves out getting there   Our problems are also now quite different  In 1986 I was trying to figure out how to get a little more speed out of small programs that involved putting a few hundred pixels on the screen  I wanted the animation to be less jerky  A fair case for assembly language  Now I m trying to figure out how to represent abstractions around contract language and servicer policy for mortgages  and I d rather read something that looks close to the language that the business folks speak  Unlike LISP macros  Assembly macros don t enforce much in the way of rules  so even though you might be able to get something reasonably close to a DSL in a good assembler  it ll be prone to all sorts of quirks that won t cause me problems if I wrote the same code in Ruby  Boo  Lisp  C  or even F    If your problems are easy to express in efficient assembly language  though  more power to you

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As a developer who spends most of his time in the embedded programming world  I would argue that assembly is far from a dead obsolete language   There is a certain close-to-the-metal level of coding  for example  in drivers  that sometimes cannot be expressed as accurately or efficiently in a higher-level language   We write nearly all of our hardware interface routines in assembler   That being said  this assembly code is wrapped such that it can be called from C code and is treated like a library   We don t write the entire program in assembly for many reasons   First and foremost is portability  our code base is used on several products that use different architectures and we want to maximize the amount of code that can be shared between them   Second is developer familiarity   Simply put  schools don t teach assembly like they used to  and our developers are far more productive in C than in assembly   Also  we have a wide variety of  extras   things like libraries  debuggers  static analysis tools  etc  available for our C code that aren t available for assembly language code   Even if we wanted to write a pure-assembly program  we would not be able to because several critical hardware libraries are only available as C libs   In one sense  it s a chicken egg problem   People are driven away from assembly because there aren t as many libraries and development debug tools available for it  but the libs tools don t exist because not enough people use assembly to warrant the effort creating them   In the end  there is a time and a place for just about any language   People use what they are most familiar and productive with   There will probably always be a place in a programmer s repertoire for assembly  but most programmers will find that they can write code in a higher-level language that is almost as efficient in far less time

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Because it s always that way  time pass and good things pass away too     But when you write asm code it s totally different feeling than when you code high-level langs  though you know it s much less productive  It s like you re a painter  you are free to draw anything you like the way you like with absolutely no restrictions well  only by CPU features     That is why I love it  It s a pity this language goes away  But while somebody still remembers it and codes it  it will never die

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A reasonable level of assembler competence is a useful skill  especially if you work at any sort of system level or embedded programming  not so much because you have to write that much assembler  but because sometimes it s important to understand what the box is really doing   If you don t have a low-level understanding of assembler concepts and issues  this can be very difficult   However  as for actually writing much code in assembler  there are several reasons it s not much done    There s simply no  almost  need   Except for something like the very early system initialization and perhaps a few assembler fragments hidden in C functions or macros  all very low-level code that might once have been written in assembler can be written in C or C   with no difficulty  Code in higher-level languages  even C and C    condenses functionality into far fewer lines  and there is considerable research showing that the number of bugs correlates with the number of lines of source code   Ie  the same problem  solved in assembler and C  will have more bugs in assembler simply because its longer   The same argument motivates the move to higher level languages such as Perl  Python  etc  Writing in assembler  you have to deal with every single aspect of the problem  from detailed memory layout  instruction selection  algorithm choices  stack management  etc   Higher level languages take all this away from you  which is why are so much denser in terms of LOC    Essentially  all of the above are related to the level of abstraction available to you in assembler versus C or some other language   Assembler forces you to make all of your own abstractions  and to maintain them through your own self-discipline  where any mid-level language like C  and especially higher level languages  provide you with abstractions out of the box  as well as the ability to create new ones relatively easily

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As others mentioned before  the reason for any tool to exist is how efficiently it can work  As HLLs can accomplish the same jobs as many lines of asm code I guess it s natural for assembly to be superseded by other languages  And for the close-to-hardware fiddling - there s inline assembly in C and other variants as per language     Dr  Paul Carter in says in the PC Assembly Language          a better understanding of how   computers really work at a lower level   than in programming languages like   Pascal  By gaining a deeper   understanding of how computers work    the reader can often be much more   productive developing software in   higher level languages such as C and   C    Learning to program in assembly   language is an excellent way to   achieve this goal     We ve got introduction to assembly in my college courses  It ll help to clear concepts  However I doubt any of us would write 90  of code in assembly  How relevant is in-depth assembly knowledge today

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What C has over a good macro assembler is the language C   Type checking   Loop constructs   Automatic stack management    Nearly  automatic variable management   Dynamic memory techniques in assembler are a massive pain in the butt   Doing a linked list properly is just down right scary compared to C or better yet list foo insert     And debugging - well  there s no contest on what is easier to debug   HLLs win hands down there   I ve coded nearly half my career in assembler which makes it very easy for me to think in assmebler   it helps me to see what the C compiler is doing which again helps me write code that the C compiler can efficiently handle   A well thought out routine written in C can be written to output exactly what you want in assembler with a little work - and it s portable   I ve already had to rewrite a few older asm routines back to C for cross platform reasons and it s no fun   No  I ll stick with C and deal with the occasional slight slowdown in performance against the productivity time I gain with HLL

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C is a macro assembler  And it s the best one   It can do nearly everything assembly can  it can be portable and in most of the rare cases where it can t do something you can still use embedded assembly code  This leaves only a small fraction of programs that you absolutely need to write in assembly and nothing but assembly   And the higher level abstractions and the portability make it more worthwhile for most people to write system software in C  And although you might not need portability now if you invest a lot of time and money in writing some program you might not want to limit yourself in what you ll be able to use it for in the future

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Assembly is not portable between different microprocessors

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I love programming in assembly language  but it takes more code to do the same thing as in a high-level languge  and there is a direct correlation between lines of code and bugs   This was explained decades ago in The Mythical Man-Month    It s possible to think of C as  high level assembly   but get a few steps above that and you re in a different world  In C  you don t think twice about writing this   foreach  string s in listOfStrings       do stuff        This would be dozens  maybe hundreds of lines of code in assembly  each programmer implementing it would take a different approach  and the next person coming along would have to figure it out  So if you believe  as many do  that programs are written primarily for other people to read  assembly is less readable than the typical HLL   Edit  I accumulated a personal library of code used for common tasks  and macros for implementing C-like control structures  But I hit the wall in the 90s  when GUIs became the norm  Too much time was being spent on things that were routine   The last task I had where ASM was essential was a few years ago  writing code to combat malware  No user interface  so it was all the fun parts without the bloat

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If an average production program has say 100k lines of code  and each line is about 8-12 assembler instructions  that would be 1 million of assembler instructions    Even if you could write all this by hand at a decent speed  remember  its 8 times more code that you have to write   what happens if you want to change some of the functionality  Understanding something you wrote a few weeks ago out of those 1 million instructions is a nightmare  There s no modules  no classes  no object-oriented design  no frameworks  no nothing  And the amount of similar looking code you have to write for even the simplest things is daunting at best   Besides  you can t optimize your code nearly as well as a high level language  Where C for example performs an insane number of optimizations because you describe your intent  not only your code  in assembler you only write code  the assembler can t really perform any note-worthy optimizations on your code  What you write is what you get  and trust me  you can t reliably optimize 1 million instructions that you patch and patch as you write it

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People seem to forget that there is also the other direction   Why are you writing in Assembler in the first place  Why not write the program in a truly low level language   Instead of   mov eax  0x123 add eax  0x456 push eax call printInt   you could just as well write  B823010000 0556040000 50  FF15        That has so many advantages  you know the exact size of your program  you can reuse  the value of instructions as input for other instructions and you do not even need an assembler to write it  you can use any text editor     And the reason you still prefer Assembler about this  is the reason other people prefer C

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I m learning assembly in comp org right now  and while it is interesting  it is also very inefficient to write in   You have to keep alot more details in your head to get things working  and its also slower to write the same things   For example  a simple 6 line for loop in C   can equal 18 lines or more of assembly   Personally  its alot of fun learning how things work down at the hardware level  and it gives me greater appreciation for how computing works

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The same reason we don t go to the bathroom outside anymore  or why we don t speak Latin or Aramaic   Technology comes along and makes things easier and more accessible   EDIT - to cease offending people  I ve removed certain words

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Hell   I am a compiler   I just scanned thousands of lines of code while you were reading this sentence  I browsed through millions of possibilities of optimizing a single line of yours using hundreds of different optimization techniques based on a vast amount of academic research that you would spend years getting at  I won t feel any embarrassment  not even a slight ick  when I convert a three-line loop to thousands of instructions just to make it faster  I have no shame to go to great lengths of optimization or to do the dirtiest tricks  And if you don t want me to  maybe for a day or two  I ll behave and do it the way you like  I can transform the methods I m using whenever you want  without even changing a single line of your code  I can even show you how your code would look in assembly  on different processor architectures and different operating systems and in different assembly conventions if you d like  Yes  all in seconds  Because  you know  I can  and you know  you can t     P S  Oh  by the way you weren t using half of the code you wrote  I did you a favor and threw it away

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I ve written shedloads of assembler for the 6502  Z80  6809 and 8086 chips  I stopped doing so as soon as C compilers became available for the platforms I was addressing  and immediately became at least 10x more productive  Most good  programmers use the tools they use for rational reasons

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When you are writing in assembly  you don t have to write just in instruction codes  You can use macros and procedures and your own conventions to make various abstractions to make programs more modular  more maintainable and easier to read   So what you re basically saying is  that with skilled use of a sophisticated assembler  you can make your ASM code closer and closer to C  or anyway another low-ish-level language of your own invention   until eventually you are just as productive as a C programmer   Does that answer your question   -   I don t say this idly  I have programmed using exactly such an assembler and system  Even better  the assembler could target a virtual processor  and a separate translator compiled the output of the assembler for a target platform  Much as happens with LLVM s IF  but in its early forms pre-dating it by about 10 years  So there was portability  plus the ability to write routines for a specific target asssembler where required for efficiency   Writing using that assembler was about as productive as C  and with by comparison with GCC-3  which was around by the time I was involved  the assembler translator produced code that was roughly as fast and usually smaller  Size was really important  and the company had few programmers and was willing to teach new hires a new language before they could do anything useful  And we had the back-up that people who didn t know the assembler  e g  customers  could write C and compile it for the same virtual processor  using the same calling convention and so on  so that it interfaced neatly  So it felt like a marginal win    That was with multiple man-years of work in the bag developing the assembler technology  libraries  and so on  Admittedly much of which went into making it portable  if it had only ever been targeting one architecture then the all-singing all-dancing assembler would have been much easier   In summary  you may not like C  but it doesn t mean that the effort of using C is greater than the effort of coming up with something better

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Oh hai  I m a dataflow system  This App I m running  are full of varrrious components  It s a distributed app  and it resides in 3 computers  on a powerful x86 and two smaller ARMs  Most of the components are written in C    but there is a critical one written in ASM for the x86  Also  most components have several variations  compiled for different processors  also some components have special GPU versions  Shame or not  I have a script component  a wrapper component calls a script   which prints report  but only once a year  It doesn t even hurt that it s just a script  a slow script  As a smart dataflow app  I know  my architecture fits only for certain tasks  where a signal data is flowing thru a graph  e g  automation  video image processing  audio processing  all synthetisers use  dataflow  but fortunatelly these appliction areas are very horsepower hungry ones  where optimization is essential  I am pretty sure that a nice day several other architectures will appear  which are also about optimisation  and about other things make programming easier etc    and they will be able to cover more or other areas  which me  the dataflow can t  So  the  quot C vs ASM quot  topic is not a real dilemma  It s like arguing of that wheter digital or analogue synths are better  as I mentioned  I m engadged with synths   I advise  make good music  Or listen  Whatever  C is not versus ASM  Anyway  I never seen a C program attacked by an ASM one or vice versa  Sorry for bad English  despite I m not a new tehcnology  I m not widely known  I m a child  A promising one  Come  see my profile

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I m sure there are many reasons  but two quick reasons I can think of are   Assembly code is definitely harder to read  I m positive its more time-consuming to write as well  When you have a huge team of developers working on a product  it is helpful to have your code divided into logical blocks and protected by interfaces

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The advantage of HLL s is even greater when you compare assembly to a higher level language than C  e g  Java or Python or Ruby   For instance  these languages have garbage collection   no need to worry about when to free a chunk of memory  and no memory leaks or bugs due to freeing too early

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In addition to other people s answers of readability  maintainability  shorter code and therefore fewer bugs  and being much easier  I ll add an additional reason   program speed    Yes  in assembly you can hand tune your code to make use of every last cycle and make it as fast as is physically possible  However who has the time  If you write a not-completely-stupid C program  the compiler will do a really good job of optimizing for you  Probably making at least 95  of the optimizations you d do by hand  without you having to worry about keeping track of any of it  There s definitely a 90 10 kind of rule here  where that last 5  of optimizations will end up taking up 95  of your time  So why bother

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Well I have been writing a lot of assembly  in the old days   and I can assure you that I am much more productive when I write programs in a high level language

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I can only answer why I personally don t write programs in assembly more often  and the main reason is that it s more tedious to do  Also  I think that it is easier to get things subtly wrong without noticing immediately  E g   you might change the way you use a register in one routine but forget to change this in one place  It ll assemble fine and you may not notice until much later   That said  I do think there are still valid uses for assembly  For instance  I have a number of pretty optimised assembly routines for processing large amounts of data  using SIMD and following the paranoid  every bit is sacred  quote V Stob  approach   But note that naive assembly implementations are often a lot worse than what a compiler would generate for you

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Portability is always an issue -- if not now  at least eventually  The programming industry spends billions every year to port old software which  at the time it was written  had  obviously  no portability issue whatsoever

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A company hires a developer to help turn code into       The faster that useful code  can be produced  the faster the company can turn that code into       Higher level languages are generally better at churning out larger volumes of useful code   This is not to say that assembly does not have its place  for there are times and places where nothing else will do

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Flipping through these answers  I d bet 9 10 of the responders have never worked with assembly    This is an ages old question that comes up every so often and you get the same  mostly misinformed answers  If it weren t for portability  I d still do everything in assembly myself  Even then  I code in C almost like I did in assembly

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Ditto most of what others have said   In the good old days before C was invented  when the only high level languages were things like COBOL and FORTRAN  there were lots of things that just weren t possible to do without resorting to assembler  It was the only way to get the full breadth of flexibility  to be able to access all the devices  etc  But then C was invented  and almost anything that was possible in assembly was possible in C  I have written very little assembly since then   That said  I think it is a very useful exercise for new programmers to learn to write in assembler  Not because they would actually use it much  but because then you understand what is really happening inside the computer  I ve seen lots of programming errors and inefficient code from programmers who clearly have no idea what s really happening with the bits and bytes and registers

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The difference is - assembler is an art of code and a good painting in a proper artist s hands  You are smarter than crappy compiler code  If you are  use it or take care of your painting with c and assembler together

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I d guess ASM on even x86  64  makes sense in cases where you gain a lot by utilizing instructions that are difficult for a compiler to optimize for  x264 for example uses a lot of asm for its encoding  and the speed gains are huge

[c] Why aren't programs written in Assembly more often?

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