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Is struct field layout consistent with endianness in C#?

When I first learned endianness, I was very confused at how it worked. I finally explained it to myself by the following metaphor:
On a big-endian machine, an int[4] would be arranged like this:
| int[4] |
|int1|int2|int3|int4|
While on little-endian machines, it would be laid out like
| int[4] |
|1tni|2tni|3tni|4tni|
That way the layout of the array would be consistent in memory, while the values themselves would be arranged differently.
Now to the real question: I am writing more optimized versions of BinaryReader and BinaryWriter in my .NET library. One of the problems I have run into is the implementation of Write(decimal). A decimal contains 4 int fields: flags, hi, lo, and mid, in that order. So basically on your typical little-endian machine it would look like this in memory:
| lamiced |
|sgalf|ih|ol|dim|
My question is, how would the CLR arrange the struct on big-endian machines? Would it arrange it so that the basic layout of the decimal would be conserved, like so
| decimal |
|flags|hi|lo|mid|
or would it completely reverse the binary arrangement of the decimal, like
| decimal |
|mid|lo|hi|flags|
?
Don't have a big-endian machine nearby, otherwise I'd test it out myself.
edit: TL;DR does the following code print -1 or 0 on big-endian machines?
struct Pair
{
public int a;
public int b;
}
unsafe static void Main()
{
var p = default(Pair);
p.a = -1;
Console.WriteLine(*(int*)&p);
}

It's not entirely clear what your actual question is.
Regarding the relationship between the layout of fields in a data structure and endianness, there is none. Endianness does not affect how fields in a data structure are laid out, only the order of bytes within a field.
I.e. in answer to this:
does the following code print -1 or 0 on big-endian machines?
… the output will be -1.
But you seem to be also or instead asking about the effect of endianness on the in-memory representation of the Decimal type. Which is a somewhat different question.
Regarding the endianness of the Decimal in-memory representation, I'm not aware of any requirement that .NET provide consistent implementations of the Decimal type. As commenter Hans Passant points out, there are multiple ways to view the current implementation; either as the CLR code you referenced, or as the more detailed declaration seen in e.g. wtypes.h or OleDb.h (another place a DECIMAL type appears, which has the same format as elsewhere). But in reality, as far as .NET is concerned, you are not promised anything about the in-memory layout of the type.
I would expect, for simplicity in implementation, the fields representing the 3 32-bit mantissa components may be affected by endianness, individually. (The sign and scale are represented as individual bytes, so endianness would not affect those). That is, while the order of the individual 32 bit fields would remain the same — high, low, mid — the bytes within each field will be represented according to the current platform's endianness.
But if Microsoft for some bizarre reason decided they wanted the .NET implementation to deviate from the native implementation (seems unlikely, but let's assume it for the sake of argument) and always use little-endian for the fields even on big-endian platforms, that would be within their rights.
For that matter, they could even rearrange the fields if they wanted to: their current order appears to me to be a concession to the de facto x86 standard of little-endianness, such that on little-endian architectures the combination of low and mid 32-bit values can be treated as a single 64-bit value without swapping words, so if they decided to deviate from the wtypes.h declaration, they might well decide to just make the mantissa a single 96-bit, little-endian or big-endian value.
Again, I'm not saying these actions are in any way likely. Just that they are theoretically possible and are just easy, obvious examples (a subset of all possible examples) of why writing managed code that assumes such private implementation details is probably not a good idea.
Even if you had access to a big-endian machine that could run .NET libraries (*) and so could test the actual behavior, today's current behavior doesn't offer you any guarantees of future behavior.
(*) (I don't even know of any…pure big-endian CPUs are fairly uncommon these days, and I can't think of a single one off the top of my head that is supported by Microsoft as an actual .NET platform.)
So…
I am skeptical that it is practical to author implementations of BinaryReader and BinaryWriter that are observably more optimized than those found in .NET already. The main reason for using these types is to handle I/O, and that necessarily means interacting with external systems that are orders of magnitude slower than the CPU that is handling the actual conversions to and from byte representations (and even the GC operations to support those conversions). Even if the existing Microsoft code were in some way hypothetically inefficient, in practice I doubt it would matter much.
But if you must implement these yourself, it seems to me that the only safe way to deal with the Decimal type is to use the Decimal.GetBits() method and Decimal.Decimal(int[]) constructor. These use clearly-documented, endian-independent mechanisms to convert the Decimal type. They are based on int, the in-memory representation of which will of course vary according to endianness, but your code will never need to worry about that, because it will only have to deal with entire int values, not their byte-wise representations.

Performance and Memory Consumption in C#

I have two question:
1) I need some expert view in terms of witting code which will be Performance and Memory Consumption wise sound enough.
2) Performance and Memory Consumption wise how good/bad is following piece of code and why ???
Need to increment the counter that could go maximum by 100 and writing code like this:
Some Sample Code is as follows:
for(int i=0;i=100;i++)
{
Some Code
}
for(long i=0;i=1000;i++)
{
Some Code
}
how good is to use Int16 or anything else instead of int, long if the requirement is same.

Need to increment the counter that could go maximum by 100 and writing code like this:
Options given:
for(int i=0;i=100;i++)
for(long i=0;i=1000;i++)
EDIT: As noted, neither of these would even actually compile, due to the middle expression being an assignment rather than an expression of type bool.
This demonstrates a hugely important point: get your code working before you make it fast. Your two loops don't do the same thing - one has an upper bound of 1000, the other has an upper bound of 100. If you have to choose between "fast" and "correct", you almost always want to pick "correct". (There are exceptions to this, of course - but that's usually in terms of absolute correctness of results across large amounts of data, not code correctness.)
Changing between the variable types here is unlikely to make any measurable difference. That's often the case with micro-optimizations. When it comes to performance, architecture is usually much more important than in-method optimizations - and it's also a lot harder to change later on. In general, you should:
Write the cleanest code you can, using types that represent your data most correctly and simply
Determine reasonable performance requirements
Measure your clean implementation
If it doesn't perform well enough, use profiling etc to work out how to improve it

DateTime dtStart = DateTime.Now;
for(int i=0;i=10000;i++)
{
Some Code
}
response.write ((DateTime.Now - dtStart).TotalMilliseconds.ToString());
same way for Long as well and you can know which one is better... ;)

When you are doing things that require a number representing iterations, or the quantity of something, you should always use int unless you have a good semantic reason to use a different type (ie data can never be negative, or it could be bigger than 2^31). Additionally, Worrying about this sort of nano-optimization concern will basically never matter when writing c# code.
That being said, if you are wondering about the differences between things like this (incrementing a 4 byte register versus incrementing 8 bytes), you can always cosult Mr. Agner's wonderful instruction tables.
On an Amd64 machine, incrementing long takes the same amount of time as incrementing int.**
On a 32 bit x86 machine, incrementing int will take less time.
** The same is true for almost all logic and math operations, as long as the value is not both memory bound and unaligned. In .NET a long will always be aligned, so the two will always be the same.

do datatype choices affect performance?

I have an object model that I use to fill results from a query and that I then pass along to a gridview.
Something like this:
public class MyObjectModel
{
public int Variable1 {get;set;}
public int VariableN {get;set;}
}
Let's say variable1 holds the value of a count and I know that the count will never get to become very large (ie. number of upcoming appointments for a certain day). For now, I've put these data types as int. Let's say it's safe to say that someone will book less than 255 appointments per day. Will changing the datatype from int to byte affect performance much? Is it worth the trouble?
Thanks

No, performance will not be affected much at all.
For each int you will be saving 3 bytes, or 6 in total for the specific example. Unless you have many millions of these, the savings in memory are very small.
Not worth the trouble.
Edit:
Just to clarify - my answer is specifically about the example code. In many cases the choices will make a difference, but it is a matter of scale and will require performance testing to ensure correct results.
To answer #Filip's comment - There is a difference between compiling an application to 64bit and selecting an isolated data type.

Using a integer variable smaller than an int (System.Int32) will not provide any performance benefits. This is because most integer operations in the CLR will promote the variable to an int prior to performing the operation. int is considered the "natural" integer size on the systems for which the CLR was developed.
Consider the following code:
for (byte appointmentIndex = 0; appointmentIndex < Variable1; appointmentIndex++)
ProcessAppointment(appointmentIndex);
In the compiled code, the comparison (appointmentIndex < Variable1) and the increment (appointmentIndex++) will (most likely) be performed using 32-bit integers. Even if the optimizer uses a smaller data type, the CPU itself will require additional work to use the smaller data type.
If you are storing an array of values, then using a smaller data type could help save space, which might give a performance advantage in some scenerios.

It will affect the amount of memory allocated for that variable. In my personal opinion, I don't think it's worth the trouble in the example case.
If there were a huge number of variables, or a database table where you could really save, then yes, but not in this case.
Besides, after years of maintenance programming, I can safely say that it's rarely safe to assume an upper limit on anything. if there's even a remote chance that some poor maintenance programmer is going to have to re-write the app because of trying to save a trivial amount of resources, it's not worth the pay-off.

The .NET runtime optimizes the use of Int32 especially for counters etc.
.NET Integer vs Int16?

Contrary to popular belief, making your data type smaller does not make access faster. In fact, it's slower. Look at bool, it's implemented as an int.
This is because internally, your CPU works with native-word-sized registers (32/64 bit these days), and you're forcing it to convert your data back and forth for no reason (well only when writing the result in memory, but it's still a penalty you could easily avoid).
Fiddling with integer widths only affects memory access, and caching specifically. This is the kind of stuff you can only figure out by profiling your application and looking at page fault counters in particular.

I agree with the other answers that performance won't be worth it. But if you're going to do it at all, go with a short instead of a byte. My rule of thumb is to pick the highest number you can imagine, multiply by 10, then use that as the basis to pick your value. So if you can't possibly imagine a value higher than 200, then use 2000 as your basis, which would mean you'd need a short.

using uint vs int [closed]

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I have observed for a while that C# programmers tend to use int everywhere, and rarely resort to uint. But I have never discovered a satisfactory answer as to why.
If interoperability is your goal, uint shouldn't appear in public APIs because not all CLI languages support unsigned integers. But that doesn't explain why int is so prevalent, even in internal classes. I suspect this is the reason uint is used sparingly in the BCL.
In C++, if you have an integer for which negative values make no sense, you choose an unsigned integer.
This clearly signifies that negative numbers are not allowed or expected, and the compiler will do some checking for you. I also suspect in the case of array indices, that the JIT can easily drop the lower bounds check.
However, when mixing int and unit types, extra care and casts will be needed.
Should uint be used more? Why?

int is shorter to type than uint.

Your observation of why uint isn't used in the BCL is the main reason, I suspect.
UInt32 is not CLS Compliant, which means that it is wholly inappropriate for use in public APIs. If you're going to be using uint in your private API, this will mean doing conversions to other types - and it's typically easier and safer to just keep the type the same.
I also suspect that this is not as common in C# development, even when C# is the only language being used, primarily because it is not common in the BCL. Developers, in general, try to (thankfully) mimic the style of the framework on which they are building - in C#'s case, this means trying to make your APIs, public and internal, look as much like the .NET Framework BCL as possible. This would mean using uint sparingly.

Normally int will suffice. If you can satisfy all of the following conditions, you can use uint:
It is not for a public API (since uint is not CLS compliant).
You don't need negative numbers.
You (might) need the additional range.
You are not using it in a comparison with < 0, as that is never true.
You are not using it in a comparison with >= 0, as that is never false.
The last requirement is often forgotten and will introduce bugs:
static void Main(string[] args)
{
if (args.Length == 0) return;
uint last = (uint)(args.Length - 1);
// This will eventually throw an IndexOutOfRangeException:
for (uint i = last; i >= 0; i--)
{
Console.WriteLine(args[i]);
}
}

1) Bad habit. Seriously. Even in C/C++.
Think of the common for pattern:
for( int i=0; i<3; i++ )
foo(i);
There's absolutely no reason to use an integer there. You will never have negative values. But almost everyone will do a simple loop that way, even if it contains (at least) two other "style" errors.
2) int is perceived as the native type of the machine.

I prefer uint to int unless a negative number is actually in the range of acceptable values. In particular, accepting an int param but throwing an ArgumentException if the number is less than zero is just silly--use a uint!
I agree that uint is underused, and I encourage everyone else to use it more.

I program at a lower level application layer where ints rarely get above 100, so negative values are not an issue (e.g. for i < myname.length() type stuff) it's just an old C habit - and shorter to type as mentioned above. However, in some cases, when interfacing to hardware where I'm dealing with event flags from devices, the uint is important in cases where a flag may use the left (highest) most bit.
Honestly, for 99.9% of my work I could easily use ushort, but int, you know, sounds sounds a lot better than ushort.

I have made a Direct3D 10 wrapper in C# & need to use uint if I want to create very large vertex buffers. Large buffers in the video card can not be represented with a signed int.
UINT is very useful & is silly to say otherwise. If anyone thinks just because they have never needed to use uint no one else will, you are wrong.

I think it is just laziness. C# is inherently a choice for development on desktops and other machines with relatively much resources.
C and C++, however, has deep roots in old systems and embedded systems where memory is sparse, so programmers are used to think carefully what datatype to use.
C# programmers are lazy, and since there are enough resources in general, nobody really optimizes memory usage (in general, not always of course). Event if a byte would be sufficient, a lot of C# programmers, including me, just use int for simplicity. Moreover, a lot of API functions accept ints, so it prevents casting.
I agree that choosing the correct datatype is good practice, but I think the main motivation is laziness.
Finally, choosing an integer is more mathematically correct. Unsigned ints don't exist in math (only natural numbers). And since most programmers have a mathematical background, using an integer is more natural.

I think a big part of the reason is that when C first came out most of the examples used int for brevity's sake. We rejoiced at not having to write integer like we did with Fortran and Pascal, and in those days we routinely used them for mundane things like array indices and loop counters. Unsigned integers were special cases for large numbers that needed that last extra bit. I think it's a natural progression that C habits continued into C# and other new languages like Python.

Some languages (e.g. many versions of Pascal) regard unsigned types as representing numeric quantities; an operation between an unsigned type and a signed type of the same size will generally be performed as though the operands were promoted to the next larger type (in some such languages, the largest type has no unsigned equivalent, so such promotion will always be possible).
Other languages (e.g. C) regard N-bit unsigned types as a group which wraps around modulo 2^N. Note that subtracting N from a member of such a group doesn't represent numerical subtraction, but rather yields the group member which, when N is added to it, would yield the original. Arguably, certain operations involving mixtures of signed and unsigned values don't really make sense and should perhaps have been forbidden, but even code which is sloppy with its specifications of things like numeric literals will usually work, and code has been written which mixes signed and unsigned types and, despite being sloppy, does work, that the spec isn't apt to change any time soon.
It's a lot easier to work exclusively with signed types than to work out all the intricacies of interactions between signed and unsigned types. Unsigned types are useful when decomposing large numbers out of smaller pieces (e.g. for serialization) or for reconstituting such numbers, but in general it's better to simply use signed numbers for things that actually represent quantities

I know this is probably an old thread but I wanted to give some clarification.
Lets take an int8 you can store –128 to 127 and it uses 1 byte that is a total of 127 positive numbers.
When you use an int8 one of the bits is used for the negative numbers -128.
When you use a Uint8 you give the negative numbers to the positive so this allows you to use 255 positive numbers with the same amount of storage 1 byte.
The only draw back is the you have now lost the capability to use negative values.
Another problem with this is not all programming languages and databases support this.
The only reason you would use this in my opinion is when you need to be efficient in like gaming programming and you have to store large non negative numbers.
This is why not many programs use this it.
The main reason is storage is not a problem and you can't use it flexibly with other software, plugins, Database, or Api's. Also for example a bank would need negative numbers to store money etc.
I hope this will help someone.

In C# is there any significant performance difference for using UInt32 vs Int32

I am porting an existing application to C# and want to improve performance wherever possible. Many existing loop counters and array references are defined as System.UInt32, instead of the Int32 I would have used.
Is there any significant performance difference for using UInt32 vs Int32?

The short answer is "No. Any performance impact will be negligible".
The correct answer is "It depends."
A better question is, "Should I use uint when I'm certain I don't need a sign?"
The reason you cannot give a definitive "yes" or "no" with regards to performance is because the target platform will ultimately determine performance. That is, the performance is dictated by whatever processor is going to be executing the code, and the instructions available. Your .NET code compiles down to Intermediate Language (IL or Bytecode). These instructions are then compiled to the target platform by the Just-In-Time (JIT) compiler as part of the Common Language Runtime (CLR). You can't control or predict what code will be generated for every user.
So knowing that the hardware is the final arbiter of performance, the question becomes, "How different is the code .NET generates for a signed versus unsigned integer?" and "Does the difference impact my application and my target platforms?"
The best way to answer these questions is to run a test.
class Program
{
static void Main(string[] args)
{
const int iterations = 100;
Console.WriteLine($"Signed: {Iterate(TestSigned, iterations)}");
Console.WriteLine($"Unsigned: {Iterate(TestUnsigned, iterations)}");
Console.Read();
}
private static void TestUnsigned()
{
uint accumulator = 0;
var max = (uint)Int32.MaxValue;
for (uint i = 0; i < max; i++) ++accumulator;
}
static void TestSigned()
{
int accumulator = 0;
var max = Int32.MaxValue;
for (int i = 0; i < max; i++) ++accumulator;
}
static TimeSpan Iterate(Action action, int count)
{
var elapsed = TimeSpan.Zero;
for (int i = 0; i < count; i++)
elapsed += Time(action);
return new TimeSpan(elapsed.Ticks / count);
}
static TimeSpan Time(Action action)
{
var sw = new Stopwatch();
sw.Start();
action();
sw.Stop();
return sw.Elapsed;
}
}
The two test methods, TestSigned and TestUnsigned, each perform ~2 million iterations of a simple increment on a signed and unsigned integer, respectively. The test code runs 100 iterations of each test and averages the results. This should weed out any potential inconsistencies. The results on my i7-5960X compiled for x64 were:
Signed: 00:00:00.5066966
Unsigned: 00:00:00.5052279
These results are nearly identical, but to get a definitive answer, we really need to look at the bytecode generated for the program. We can use ILDASM as part of the .NET SDK to inspect the code in the assembly generated by the compiler.
Here, we can see that the C# compiler favors signed integers and actually performs most operations natively as signed integers and only ever treats the value in-memory as unsigned when comparing for the branch (a.k.a jump or if). Despite the fact that we're using an unsigned integer for both the iterator AND the accumulator in TestUnsigned, the code is nearly identical to the TestSigned method except for a single instruction: IL_0016. A quick glance at the ECMA spec describes the difference:
blt.un.s :
Branch to target if less than (unsigned or unordered), short form.
blt.s :
Branch to target if less than, short form.
Being such a common instruction, it's safe to assume that most modern high-power processors will have hardware instructions for both operations and they'll very likely execute in the same number of cycles, but this is not guaranteed. A low-power processor may have fewer instructions and not have a branch for unsigned int. In this case, the JIT compiler may have to emit multiple hardware instructions (A conversion first, then a branch, for instance) to execute the blt.un.s IL instruction. Even if this is the case, these additional instructions would be basic and probably wouldn't impact the performance significantly.
So in terms of performance, the long answer is "It is unlikely that there will be a performance difference at all between using a signed or an unsigned integer. If there is a difference, it is likely to be negligible."
So then if the performance is identical, the next logical question is, "Should I use an unsigned value when I'm certain I don't need a sign?"
There are two things to consider here: first, unsigned integers are NOT CLS-compliant, meaning that you may run into issues if you're exposing an unsigned integer as part of an API that another program will consume (such as if you're distributing a reusable library). Second, most operations in .NET, including the method signatures exposed by the BCL (for the reason above), use a signed integer. So if you plan on actually using your unsigned integer, you'll likely find yourself casting it quite a bit. This is going to have a very small performance hit and will make your code a little messier. In the end, it's probably not worth it.
TLDR; back in my C++ days, I'd say "Use whatever is most appropriate and let the compiler sort the rest out." C# is not quite as cut-and-dry, so I would say this for .NET: There's really no performance difference between a signed and unsigned integer on x86/x64, but most operations require a signed integer, so unless you really NEED to restrict the values to positive ONLY or you really NEED the extra range that the sign bit eats, stick with a signed integer. Your code will be cleaner in the end.

I don't think there are any performance considerations, other than possible difference between signed and unsigned arithmetic at the processor level but at that point I think the differences are moot.
The bigger difference is in the CLS compliance as the unsigned types are not CLS compliant as not all languages support them.

I haven't done any research on the matter in .NET, but in the olden days of Win32/C++, if you wanted to cast a "signed int" to a "signed long", the cpu had to run an op to extend the sign. To cast an "unsigned int" to an "unsigned long", it just had stuff zero in the upper bytes. Savings was on the order of a couple of clock cycles (i.e., you'd have to do it billions of times to have an even perceivable difference)

There is no difference, performance wise. Simple integer calculations are well known and modern cpu's are highly optimized to perform them quickly.

These types of optimizations are rarely worth the effort. Use the data type that is most appropriate for the task and leave it at that. If this thing so much as touches a database you could probably find a dozen tweaks in the DB design, query syntax or indexing strategy that would offset a code optimization in C# by a few hundred orders of magnitude.

Its going to allocate the same amount of memory either way (although the one can store a larger value, as its not saving space for the sign). So I doubt you'll see a 'performance' difference, unless you use large values / negative values that will cause one option or the other to explode.

this isn't really to do with performance rather requirements for the loop counter.
Prehaps there were lots of iterations to complete
Console.WriteLine(Int32.MaxValue); // Max interation 2147483647
Console.WriteLine(UInt32.MaxValue); // Max interation 4294967295
The unsigned int may be there for a reason.

I've never empathized with the use of int in loops for(int i=0;i<bla;i++). And oftentimes I would also like to use unsigned just to avoid checking the range. Unfortunately (both in C++ and for similar reasons in C#), the recommendation is to not use unsigned to gain one more bit or to ensure non-negativity, :
"Using an unsigned instead of an int to gain one more bit to represent positive integers is almost never a good idea. Attempts to ensure that some values are positive by declaring variables unsigned will typically be defeated by the implicit conversion rules"
page 73 from "The C++ Programming Language" by the language's creator Bjarne Stroustrup.
My understanding (I apologize for not having the source at hand) is that hardware makers also have a bias to optimize for integer types.
Nonetheless, it would be interesting to do the same exercise that #Robear did above but using integer with some positivity assert versus unsigned.