Currently, I am using signed values, -2^63 to 2^63-1. Now I need the same range (2 * 2^64), but with positive values only. I found the java documentations mentioning unsigned long, which suits this use.
I tried to declare 2^64 to a Long wrapper object, but it still loses the data, in other words, it only captures till the Long.MAX_VALUE, so I am clearly missing something.
Is BigInteger the signed long that Java supports?
Is there a definition or pointer as to how to declare and use it?
In Java 8, unsigned long support was introduced. Still, these are typical longs, but the sign doesn't affect adding and subtracting. For dividing and comparing, you have dedicated methods in Long. Also, you can do the following:
long l1 = Long.parseUnsignedLong("12345678901234567890");
String l1Str = Long.toUnsignedString(l1)
BigInteger is a bit different. It can keep huge numbers. It stores them as int[] and supports arithmetic.
Although Java has no unsigned long type, you can treat signed 64-bit two's-complement integers (i.e. long values) as unsigned if you are careful about it.
Many primitive integer operations are sign agnostic for two's-complement representations. For example, you can use Java primitive addition, subtraction and multiplication on an unsigned number represented as a long, and get the "right" answer.
For other operations such as division and comparison, the Long class provides method like divideUnsigned and compareUnsigned that will give the correct results for unsigned numbers represented as long values.
The Long methods supporting unsigned operations were added in Java 8. Prior to that, you could use 3rd-party libraries to achieve the same effect. For example, the static methods in the Guava UnsignedLongs class.
Is BigInteger the signed long that Java supports?
BigInteger would be another way to represent integer values greater that Long.MAX_VALUE. But BigInteger is a heavy-weight class. It is unnecessary if your numbers all fall within the range 0 to 264 - 1 (inclusive).
If using a third party library is an option, there is jOOU (a spin off library from jOOQ), which offers wrapper types for unsigned integer numbers in Java. That's not exactly the same thing as having primitive type (and thus byte code) support for unsigned types, but perhaps it's still good enough for your use-case.
import static org.joou.Unsigned.*;
// and then...
UByte b = ubyte(1);
UShort s = ushort(1);
UInteger i = uint(1);
ULong l = ulong(1);
All of these types extend java.lang.Number and can be converted into higher-order primitive types and BigInteger. In your case, earlier versions of jOOU simply stored the unsigned long value in a BigInteger. Version 0.9.3 does some cool bit shifting to fit the value in an ordinary long.
(Disclaimer: I work for the company behind these libraries)
Related
go has the constant MaxUint32, for insigned integers, but does Java have an equivalent constant? Cuz I noticed that MaxUint32 is 4294967295 and Integer.MAX_VALUE is 2x that.
What would be the java equivalent of
r := float64(stringHash(source)) / (float64(math.MaxUint32) + 1)
What's the difference between a float in Java and a float64 in go?
According to this Question on Stack Overflow, MaxUint32 is a constant for the maximum 32-bit number available within in the Go type system, ranging from 0 to 4,294,967,295.
As for Java, I can explain that Java has only signed numeric types. As commented by tgdavies, that means the largest signed 32-bit integer in Java is half that of the unsigned 32-bit integer in Go: 2,147,483,647. As a workaround for compatibility with Go, just us a 64-bit long in Java to accommodate values coming in from Go.
In recent years a facility was added to address numbers as if unsigned. But I believe that should be used only on an exceptional basis. See Declaring an unsigned int in Java, especially this Answer.
And I can quote from The Java Tutorials, provided free-of-cost by Oracle corp, which you should read before posting here on basic Java matters:
The eight primitive data types supported by the Java programming language are:
byte: The byte data type is an 8-bit signed two's complement integer. It has a minimum value of -128 and a maximum value of 127 (inclusive). The byte data type can be useful for saving memory in large arrays, where the memory savings actually matters. They can also be used in place of int where their limits help to clarify your code; the fact that a variable's range is limited can serve as a form of documentation.
short: The short data type is a 16-bit signed two's complement integer. It has a minimum value of -32,768 and a maximum value of 32,767 (inclusive). As with byte, the same guidelines apply: you can use a short to save memory in large arrays, in situations where the memory savings actually matters.
int: By default, the int data type is a 32-bit signed two's complement integer, which has a minimum value of -231 and a maximum value of 231-1. In Java SE 8 and later, you can use the int data type to represent an unsigned 32-bit integer, which has a minimum value of 0 and a maximum value of 232-1. Use the Integer class to use int data type as an unsigned integer. See the section The Number Classes for more information. Static methods like compareUnsigned, divideUnsigned etc have been added to the Integer class to support the arithmetic operations for unsigned integers.
long: The long data type is a 64-bit two's complement integer. The signed long has a minimum value of -263 and a maximum value of 263-1. In Java SE 8 and later, you can use the long data type to represent an unsigned 64-bit long, which has a minimum value of 0 and a maximum value of 264-1. Use this data type when you need a range of values wider than those provided by int. The Long class also contains methods like compareUnsigned, divideUnsigned etc to support arithmetic operations for unsigned long.
float: The float data type is a single-precision 32-bit IEEE 754 floating point. Its range of values is beyond the scope of this discussion, but is specified in the Floating-Point Types, Formats, and Values section of the Java Language Specification. As with the recommendations for byte and short, use a float (instead of double) if you need to save memory in large arrays of floating point numbers. This data type should never be used for precise values, such as currency. For that, you will need to use the java.math.BigDecimal class instead. Numbers and Strings covers BigDecimal and other useful classes provided by the Java platform.
double: The double data type is a double-precision 64-bit IEEE 754 floating point. Its range of values is beyond the scope of this discussion, but is specified in the Floating-Point Types, Formats, and Values section of the Java Language Specification. For decimal values, this data type is generally the default choice. As mentioned above, this data type should never be used for precise values, such as currency.
boolean: The boolean data type has only two possible values: true and false. Use this data type for simple flags that track true/false conditions. This data type represents one bit of information, but its "size" isn't something that's precisely defined.
char: The char data type is a single 16-bit Unicode character. It has a minimum value of '\u0000' (or 0) and a maximum value of '\uffff' (or 65,535 inclusive).
That last one, char, is legacy, and should generally be avoided in favor of using code point integer numbers.
All of those primitive types have wrapper classes, when you need an object.
For extra large integers, use BigInteger class.
For extra large/small fractional numbers, use BigDecimal. Also use BigDecimal when you need accuracy rather than speed-of-execution. Uses cases include fractional money matters.
I'm reading a file format that specifies some types are unsigned integers and shorts. When I read the values, I get them as a byte array. The best route to turning them into shorts/ints/longs I've seen is something like this:
ByteBuffer wrapped = ByteBuffer.wrap(byteArray);
int x = wrapped.getInt();
That looks like it could easily overflow for unsigned ints. Is there a better way to handle this scenario?
Update: I should mention that I'm using Groovy, so I absolutely don't care if I have to use a BigInteger or something like that. I just want the maximum safety on keeping the value intact.
A 32bit value, signed or unsigned, can always be stored losslessly in an int*. This means that you never have to worry about putting unsigned values in signed types from a data safety point of view.
The same is true for 8bit values in bytes, 16bit values in shorts and 64bit values in longs.
Once you've read an unsigned value into the corresponding signed type, you can promote them to signed values of a larger types to more easily work with the intended value:
Integer.toUnsignedLong(int)
Short.toUnsignedInt(short)
Byte.toUnsignedInt(byte)
Since there's no primitive type larger than long, you can either go via BigInteger, or use the convenience methods on Long to do unsigned operations:
BigInteger.valueOf(Long.toUnsignedString(long))
Long.divideUnsigned(long,long) and friends
* This is thanks to the JVM requiring integer types to be two's complement.
To hold an unsigned int/short/byte, you need to use the next "bigger" type, i.e. long/int/short. If you already hold the value in the signed type that can overflow, the conversion can be done by doing the following:
int unsignedVal = byteVal & 0xff
If you just cast them, the negative-bit will be regarded and you will still end up with the negative value.
If you have to handle unsigned longs you need to "switch" to java.math.BigInteger.
Unsigned primitives are a pain in Java.
There's no clean way of handing them, except using larger types with more bits, and taking care to avoid automatic sign extension when casting.
In your case, you can do something like this:
ByteBuffer wrapped = ByteBuffer.wrap(byteArray);
int signedInt = wrapped.getInt();
long unsigned = signedInt & 0xffffffffL;
I usually write the required conversion(s) in a utility class someplace, since they're easy to get wrong. If you copy & paste that one liner conversion everywhere, eventually one will be wrong.
Note that if you need unsigned longs, the only larger type is BigInteger.
If you need anything more than simple conversions, I suggest using Guava since it has some nice classes for dealing with unsigned types. See documentation here.
as we know Java doesn't support unsigned operations because it considers the last bit as a sign bit for all integers.
I know that one way is to use a greater size defined for the numbers involving in the operations. for example if you want to have 32-bit operations, you can do them by long which is 64-bit, then consider the bottom 32 bits as the result.
but the point is that, it takes twofold memory.
I read something about using the class integer but i didn't understand it. Do you have any idea to do unsigned operations with the least memory used?
thanks!
"signed" and "unsigned" is about the interpretation of bit patterns as numeric values. And most (all?) modern CPUs (and the JVM) use Two's Complement representation for signed numbers, having the interesting property that for addition and subtraction, the bit pattern operations are the same as for unsigned numbers.
E.g. In 16-bit, the pattern 0xfff0 is 65520 when interpreted as an unsigned, and -16 as signed number. Subtracting 16 (0x0010) from that number gives 0xffe0, which represents the correct result both for the signed (being -32) as well as the unsigned case (65504).
So, depending on the operations you are doing on your numbers, there are cases where you can simply ignore the signed/unsigned question - just be careful with input and output.
Regarding the relevance of using the shorter representation, only you can tell. And Java can be quite fast when doing numerics. I remember a coding contest quite some years ago where even Java 1.4 outperformed Microsoft C (both with default settings - with optimization switches C was a bit faster).
As we know Java doesn't support unsigned operations because it considers the last bit as a sign bit for all integers.
This is incorrect.
While Java does not support 32 and 64 bit unsigned integer types, it DOES support unsigned integer operations; see the javadoc for the Integer and Long types, and look for the xxxUnsigned methods.
Note that you won't see methods for add, subtract or multiply because they would return the same representations as the primitive operators do.
In short, you can use the 32 bit signed int type to do 32 bit unsigned arithmetic and comparison operations.
For more information:
Java8 unsigned arithmetic
How to use the unsigned Integer in Java 8 and Java 9?
Unsigned long in Java
https://www.baeldung.com/java-unsigned-arithmetic
In C++, I enjoyed having access to a 64 bit unsigned integer, via unsigned long long int, or via uint64_t. Now, in Java longs are 64 bits, I know. However, they are signed.
Is there an unsigned long (long) available as a Java primitive? How do I use it?
Starting Java 8, there is support for unsigned long (unsigned 64 bits). The way you can use it is:
Long l1 = Long.parseUnsignedLong("17916881237904312345");
To print it, you can not simply print l1, but you have to first:
String l1Str = Long.toUnsignedString(l1)
Then
System.out.println(l1Str);
I don't believe so. Once you want to go bigger than a signed long, I think BigInteger is the only (out of the box) way to go.
Nope, there is not. You'll have to use the primitive long data type and deal with signedness issues, or use a class such as BigInteger.
No, there isn't. The designers of Java are on record as saying they didn't like unsigned ints. Use a BigInteger instead. See this question for details.
Java 8 provides a set of unsigned long operations that allows you to directly treat those Long variables as unsigned Long, here're some commonly used ones:
String toUnsignedString(long i)
int compareUnsigned(long x, long y)
long divideUnsigned(long dividend, long divisor)
long remainderUnsigned(long dividend, long divisor)
And additions, subtractions, and multiplications are the same for signed and unsigned longs.
Depending on the operations you intend to perform, the outcome is much the same, signed or unsigned. However, unless you are using trivial operations you will end up using BigInteger.
For unsigned long you can use UnsignedLong class from Guava library:
It supports various operations:
plus
minus
times
mod
dividedBy
The thing that seems missing at the moment are byte shift operators. If you need those you can use BigInteger from Java.
Java does not have unsigned types. As already mentioned, incure the overhead of BigInteger or use JNI to access native code.
The org.apache.axis.types package has a
UnsignedLong class.
for maven:
<dependency>
<groupId>org.apache.axis</groupId>
<artifactId>axis</artifactId>
<version>1.4</version>
</dependency>
Seems like in Java 8 some methods are added to Long to treat old good [signed] long as unsigned. Seems like a workaround, but may help sometimes.
I need to convert a piece of code from Objective-C to Java, but I have a problem understanding the Primitive Types in Objective-C. So I had their data types in my Objective-C code :
UInt64, Uint32, UInt8 ,
which are unsigned integers (as I understand from internet). So my question is, can I use Java primitive types like byte (8bit) - instead of UInt8, int (32bit) - instead of UInt32, and long (64bit) - instead of UInt64.
Unfortunately, it isn't a straight translation and without knowing more about your program, its hard to suggest what the "right" approach is.
If your UInt8 values really range from 0-255, you may have to use Java signed int to be able to hold the entire range.
If you are dealing with byte streams or memory layouts and really need to use just a single byte of memory, than you could try byte, but you may have to test and handle cases to handle when the high-bit is set (value > 127). Ditto with the other unsigned types.
Ideally, if your code just kind of "defaulted" to the unsigned types, but really the signed versions would have worked fine too (i.e. the ranges of your values never equal or exceed 2^7, 2^15, or 2^31 respectively), then you may be fine with the "straight" translation to byte, int, and long.
Yes, those are the correctly sized data types to use in Java. Make sure you take into account that Java does not have unsigned types and the trick is to use the next largest size. 64 bit unsigned arithmetic requires special consideration.