CODEWITHSUNDEEP
javac++bitwise-operators
user2092895
user2092895

Reputation: 13

bit operations in java, compared to c

i am trying to convert a c++ software in java, however the bit operations don't produce the same results. overview of what i am doing: there's an ascii file with data entries, 2 bytes long, unsigned (0-65535). Now i want to convert the two-byte unsigned int in two one-byte unsigned short ints.

C++ code:

signed char * pINT8;
signed char ACCBuf[3];
UInt16 tempBuf[128];


tempBuf[0] = Convert::ToUInt16(line);
pINT8 = (signed char *)&tempBuf[0];
ACCBuf[0] = *pINT8;
pINT8++;
ACCBuf[1] = *pINT8;

Java code:

int[] ACCBuf = new int[6];
int[] tempBuf = new int[128];
tempBuf[0] = Integer.parseInt(line);
ACCBuf[0] = tempBuf[0] >> 8;
ACCBuf[1] = 0x00FF & tempBuf[0];

this two codes produce different results. any idea why?

Upvotes: 1

Views: 247

Answers (1)

Olaf Dietsche
Olaf Dietsche

Reputation: 74028

This might depend on the endianess of the system. The C++ code has the lower byte in ACCBUF[0], if it is a little endian system. The Java code has the upper byte in ACCBUF[0], no matter what hardware.

If you want to get the same result in Java, you must swap the high and low byte 

ACCBuf[0] = 0x00FF & tempBuf[0];
ACCBuf[1] = tempBuf[0] >> 8;

now you will have the same bits in either Java or C++.

Another difference between the two code snippets are the types used. You have 32 bit ints in the Java code and 16 bit unsigned ints respectively 8 bit chars in C++. This isn't relevant here, but must be kept in mind, when comparing different code snippets.

Upvotes: 1

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