C bit shift tricks of the trade
However by dumb luck, this loop idiom will probably work for large sizes — because even after i overflows, it gets converted to unsigned int for the comparison operation, and after i is incremented sufficiently many times the comparison will eventually yield false and terminate the loop. But when the upper bound is unsigned int , I have to choose either the laziness of using int or the correctness of using unsigned int. This pointless check always yields false , of course.
This gives evidence that programmers make mistakes in carefully distinguishing signed and unsigned integer types in practice. Now if you want to write loops to perform signal processing on the pixels, you must use unsigned variables to count the ranges [0, width and [0, height. In other words, you must write: A wider signed type can always represent narrower unsigned types.
For example, int32 can represent all uint31 values. But the reverse is not true; no unsigned type can represent all the values of a signed type namely the negative ones are always left out. This is more or less the situation in Java. People have made the observation that programming primarily involves unsigned numbers starting from 0 , which is indeed true.
However, one needs to make use of negative numbers occasionally such as when subtracting two unsigned indexes , so signed types must exist in a programming language too. Unsigned and signed types are both useful, but signed types have strictly more functionality than unsigned types.
Thus it is clear that if language simplicity is desired, then unsigned types are the ones that can be safely omitted. Bytes are a different story however. I argue that signed bytes make programming needlessly annoying, and that only unsigned bytes should have been implemented in the first place: However in light of this small gain, there are some serious drawbacks. First, negative numbers can be used to signal error conditions, such as String. They also provide headroom to detect some instances of accidental overflows, such as NegativeArraySizeException when creating a negative-sized array or ArrayIndexOutOfBoundsException when accessing a negative array index.
Second, it detracts from the more important long-term goal of upgrading to fully bit addressing. There are some examples of small addressing gains outside of Java.
But again this is a small gain compared to switching to a fully bit kernel and user processes. Being able to outlaw negative values can be useful in certain cases. For example, data sizes are never negative, so when putting these values in signed types it takes extra effort to explicitly check that the values are are not negative.
Also, bounds checking on unsigned types only needs to check the upper bound, whereas signed types also need to check non-negativity. There are a couple of reasonable ways to implement a Foo library in Java:. Adding unsigned types would increase the already-cluttered Java standard library API. Arrays defines these method variants for filling an entire array:. The set of methods above is already a mouthful. Other parts of Java that must change include the reflection library , the JVM specification , the Java Native Interface specification , etc.
I have successfully implemented in Java numerous low-level libraries that conceptually require unsigned arithmetic. These libraries include cryptographic ciphers and hash functions, random number generators, big integer operations, and data compression. GoingNative — Interactive Panel: The relevant excerpt starts at 42min 39sec:. Could you elaborate on not using unsigned ints, unsigned types, unless you want to do bit arithmetic? Because it means I would need to revise my code review policy.
The rules are just very surprising, and they turn up in code in strange places; they correlate very strongly with bugs. Now, when people use unsigned numbers, they usually have a reason.
It is just highly error-prone. Then still use something signed until you really need something different. Then resort to unsigned. And that is only on a bit system or less, and it just does not come up in practice very much. How frequently have you written arithmetic and wanted mod-2 behavior?
Unsigned integer types do not belong in the Java programming language. They add considerable complexity to the type system, type conversion rules, library APIs, and the language and virtual machine specifications. Yet for developers who truly need unsigned arithmetic, this functionality can already be achieved effectively using signed integer types with only a small amount of knowledge and effort.
Unsigned int considered harmful for Java Introduction Every now and then, a developer comes along and complains about the lack of unsigned integer types in Java, demanding that they be implemented in the language. Continuing the previous example, this is the efficient Java translation: Otherwise, here is some non-trivial code I wrote for unsigned bit division: Bytes are a different story however.
I argue that signed bytes make programming needlessly annoying, and that only unsigned bytes should have been implemented in the first place: However in light of this small gain, there are some serious drawbacks. First, negative numbers can be used to signal error conditions, such as String. They also provide headroom to detect some instances of accidental overflows, such as NegativeArraySizeException when creating a negative-sized array or ArrayIndexOutOfBoundsException when accessing a negative array index.
Second, it detracts from the more important long-term goal of upgrading to fully bit addressing. There are some examples of small addressing gains outside of Java. But again this is a small gain compared to switching to a fully bit kernel and user processes. Being able to outlaw negative values can be useful in certain cases. For example, data sizes are never negative, so when putting these values in signed types it takes extra effort to explicitly check that the values are are not negative.
Also, bounds checking on unsigned types only needs to check the upper bound, whereas signed types also need to check non-negativity. There are a couple of reasonable ways to implement a Foo library in Java:. Adding unsigned types would increase the already-cluttered Java standard library API. Arrays defines these method variants for filling an entire array:. The set of methods above is already a mouthful.
Other parts of Java that must change include the reflection library , the JVM specification , the Java Native Interface specification , etc. I have successfully implemented in Java numerous low-level libraries that conceptually require unsigned arithmetic.
These libraries include cryptographic ciphers and hash functions, random number generators, big integer operations, and data compression. GoingNative — Interactive Panel: The relevant excerpt starts at 42min 39sec:. Could you elaborate on not using unsigned ints, unsigned types, unless you want to do bit arithmetic? Because it means I would need to revise my code review policy.
The rules are just very surprising, and they turn up in code in strange places; they correlate very strongly with bugs. Now, when people use unsigned numbers, they usually have a reason. It is just highly error-prone. Then still use something signed until you really need something different.
Then resort to unsigned. And that is only on a bit system or less, and it just does not come up in practice very much. How frequently have you written arithmetic and wanted mod-2 behavior? Unsigned integer types do not belong in the Java programming language.
They add considerable complexity to the type system, type conversion rules, library APIs, and the language and virtual machine specifications. Yet for developers who truly need unsigned arithmetic, this functionality can already be achieved effectively using signed integer types with only a small amount of knowledge and effort.
Unsigned int considered harmful for Java Introduction Every now and then, a developer comes along and complains about the lack of unsigned integer types in Java, demanding that they be implemented in the language.
Continuing the previous example, this is the efficient Java translation: Otherwise, here is some non-trivial code I wrote for unsigned bit division: To convert a uint32 to a string, this algorithm can be used: Mixed-type arithmetic pitfalls Type conversion rules When a programming language has both signed and unsigned integer types, it means that they will interact with each other in some way or another.
If both operands have the same type, then no further conversion is needed. Usage examples Mixed-type computations easily lead to subtle problems. Other considerations A wider signed type can always represent narrower unsigned types.
There are a couple of reasonable ways to implement a Foo library in Java: Arrays defines these method variants for filling an entire array: Ask Us Anything Video available on: The relevant excerpt starts at 42min 39sec: Conclusion Unsigned integer types do not belong in the Java programming language. Unsigned arithmetic in Java Joseph D. Danger — unsigned types used here!