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A byte has 8-bits. Can it be larger in another system? Give an example.
Also, how many different types of calls such as writeint,writedec,writestring,writechar are there in assembly language.
Thanks.
Not any more. There was a time, yes, when there were systems without a fundamental 8-bit byte.
System where 1 byte != 8 bit?
how many different types of call such as writeint,writedec,writestring,writechar are there in assembly language
This question makes no sense. Assembly language is just a means of writing code that translates directly to machine instructions. call is just one of these instructions - it jumps to some other section of code, with the intent of returning to the place where the call was made.
The things you're referring to sound more like library routines - in which case there are any number of them, depending on the programming environment.
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Why does the C language have an enum type but not a range type as Pascal does?
In Pascal we write this: type index = 1...100; or like this:
type letter = 'a'...'z';.
The designers of the C language implemented a very simple language whose features were only those that could be (for the most part) directly translated into to one or a handful of machine-code instructions. Anything that could not be done easily by the CPU had to be provided by a function call.
This makes the compiler very easy to write and also ensures that it is easier to see where performance problems might be.
Implementing a range takes several machine code instructions. Also, if it is used as a type qualifier it means that range checking has to be added to all arithmetic operations which requires further machine code instructions.
There are a lot of other constructs that are supported by other languages that are not supported in C except through function calls (dynamic memory allocation, string manipulation, maps, etc).
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I know that endianess little or big is inherent to the system. Then, how is it possible to change using c code, as I have seen a code, which says it can change the endianess.
Endianess depends on the CPU hardware. So normally you can't do anything about it.
The code you have seen was most likely just tossing bytes around from one endianess to the other. Though some CPUs (for example some PowerPC) do have the possibility to configure endianess by writes to a hardware register.
You can't change the endianness of the system in general (there are bi-endian architectures), this would require you to change the instruction set. You can change the endianness of the data you use though. Take a look at this question to see how.
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This is a slightly subjective answer, but how large do you think a structure should be before you start using pointers to it in other structures or function calls rather than the structure by-value?
Depends on the compiler and architecture.
C and C++ define the size of the types they use, and how functions are written, but they don't define how they are implemented.
This is means the standard itself doesn't define how the structurs are passed, just that they are in essence copied.
The compiler might decide to do something else entirely, like not copying the struct at all if there's a default copy constructor , and the variable isn't used.
But after saying all that, most common-sense compiler implementations would store the struct in a register if it fits. So depends on the architecture, make sure the structure fits in a register.
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I'm making a virtual machine in C and I was told that by converting the "assembly" code into hexadecimal or binary, I could speed up the execution. My question is, if I have a string and I encode it to numbers, how can it be faster than not encoding it when it adds and extra step to the execution in the VM?
--EDIT--
An example of the VM assembly is:
push 10 # Push the value 10 to the top of the stack
print # Print the value at the top of the stack
The encoded instructions look like this:
010a 0c
But the part I don't get is how encoding the assembly into instructions can be faster than not doing it because you have to decode them again. Please let me know if I'm wrong though.
Yes, encoding is better in the case on the re-use of the code.
Keep in mind that a function or piece of code is called many times, and so you loose little times for the first conversion and after you gain a lot of time when you start interpret the same code.
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Today I stumbled upon one simple part of code and I would like to know more people opinion.
What would be the fastest code to evaluate this graph
There is no such thing as the fastest code to evaluate this graph. It depends on the processor architecture. What can be faster on one architecture, will be slower on another, or not even possible.
Nowadays, the compilers excel at block optimizations, and you should write the code as natural as you can and let the compiler decide what "the fastest" means. If the compiler doesn't have an optimization option, the best way to handle this type of conditions is to use 'conditional move' instructions, because they do not stall the pipeline, but this is very much specific to certain architectures.