问题
how does one write a hexadecimal integer literal that is equal to Int.MIN_VALUE
(which is -2147483648
in decimal) in Kotlin?
AFAIK, an Int is 4 bytes...and sometimes it seems like 2's complement is used to represent integers...but I'm not sure. I've tried the following hex literals to help myself understand the system:
0xFFFFFFFF
but this is aLong
, not anInt
0xFFFFFFFF.toInt()
which is -1-0xFFFFFFFF.toInt()
which is 10x7FFFFFFF
which is 2147483647 which isInt.MAX_VALUE
-0x7FFFFFFF
which is -2147483647 which isInt.MIN_VALUE+1
0xFFFFFFF
which is 268435455 in decimal0x0FFFFFFF
which is also 268435455 in decimal
But I can't figure out what hexadecimal integer literal can be used to represent Int.MIN_VALUE
.
I hope the answer doesn't make me feel stupid...
回答1:
Int represents a 32-bit signed integer. 32 bits means 8 hex digits:
___7 F F F F F F F
0111 1111 1111 1111 1111 1111 1111 1111
As you can see the left-most bit is 0 thus this is a positive integral in a 32 bit representation. By 2's complement definition and example the minimal 32-bit negative value will have 1
at left-most bit followed by 0
:
1000 0000 0000 0000 0000 0000 0000 0000
___8 0 0 0 0 0 0 0
that is 0x80000000
.
In Kotlin you need to prepend the -
sign to denote negative Int
which is not true in Java. Consider following example
println(0x7FFFFFFF) // -> prints 2147483647 (Integer.MAX_VALUE)
println(-0x80000000) // -> prints -2147483648 (Integer.MIN_VALUE)
println(0x80000000) // -> prints 2147483648 (does not fit into Int)
It's not the same as in Java:
System.out.println(0x7FFFFFFF); // -> prints 2147483647 (Integer.MAX_VALUE)
System.out.println(-0x80000000); // -> prints -2147483648 (Integer.MIN_VALUE)
System.out.println(0x80000000); // -> prints -2147483648 (Integer.MIN_VALUE)
This is in line with Kotlin spec although the overflow behavior of hexadecimal literals is yet to be defined.
Further reading:
- Why is Java able to store 0xff000000 as an int?
来源:https://stackoverflow.com/questions/38175798/write-a-hexadecimal-integer-literal-equal-to-int-min-value-in-kotlin