I am puzzled by a Java data type question. I

Question

I am puzzled by a Java data type question. I

would assume that a primitive boolean would only take 1 bit of storage, but it seems it takes 8 bits (according to Oracle JVM doc)

Moreover, the Oracle tutorial says that the size is not precisely defined. I understand that other JVM implementations may have different implementation for booleans, but why? This makes it so much more confusing

0

02.01.2024

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BinaryByter

If you want to optimize for storage capability, you can store your bits in bytes and evaluate each position using bitmasks. Only really valuable if you have > 8*<length of your unpacking code> booleans to store

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02.01.2024

Roy Автор вопроса

BinaryByter
If you want to optimize for storage capability, yo...

yes, that is what I am trying to go for

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02.01.2024

BinaryByter

The reason that boolean sizes aren't defined is that its not relevant for functionality but that you want booleans to fetch as quickly as possible. X86 can fetch BYTE, WORD, DWORD, QWORD and is optimized for fetching blocks of four (QWORD) - hence why you want to align your structures on qword boundaries

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02.01.2024

BinaryByter

BinaryByter
The reason that boolean sizes aren't defined is th...

https://cdrdv2-public.intel.com/671488/248966-046A-software-optimization-manual.pdf See chapter 3.4.1.4

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02.01.2024

Roy Автор вопроса

BinaryByter
The reason that boolean sizes aren't defined is th...

got it. We (I) usually never have to think on this low level. Mechanical un-sympathetic 😂

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02.01.2024

BinaryByter

BinaryByter
If you want to optimize for storage capability, yo...

do this

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02.01.2024

BinaryByter

BinaryByter
do this

In c++ its a structure called bitset https://cplusplus.com/reference/bitset/bitset/

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02.01.2024

Roy Автор вопроса

BinaryByter
If you want to optimize for storage capability, yo...

Стикер

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02.01.2024

BinaryByter

Basically, you need many bools

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02.01.2024

Roy Автор вопроса

BinaryByter
In c++ its a structure called bitset https://cplus...

Java also has it, no?

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02.01.2024

BinaryByter

Roy
Java also has it, no?

Javas Bitset does not optimize for size

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02.01.2024

Roy Автор вопроса

BinaryByter
Javas Bitset does not optimize for size

yes, let's ignore that for now

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02.01.2024

BinaryByter

Roy
yes, let's ignore that for now

Do we want to optimize for size or no?

0

02.01.2024

Roy Автор вопроса

BinaryByter
Do we want to optimize for size or no?

yes, optimize for size

0

02.01.2024

Sebastian Dicke · Accepted Answer

Sebastian Dicke

It is impossible to fetch a singke bit from memory, most assembly languages do not support that. To store a boolean as a single bit would come with much memory management effort. Such ways of data access exist, for example in C++ with std::vector<bool>, but are not suitable for a general use data type as a primitive boolean.

0

02.01.2024

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