Merge two bytes in java/android

Question

I have a frame of 22 bytes. The frame is the input stream from an accelerometer via bluetooth. The acceleromter readings are a 16 bit number split over two bytes.

When i try to merge the bytes with buffer[1] + buffer[2], rather than adding the bytes, it just puts the results side by side. so 1+2 = 12.

Could someone tell me how to combine these two bytes to obtain the original number. (btw the bytes are sent little endian)

Thanks

Look into bitwise and bit-shift operations. leepoint.net/notes-java/data/expressions/bitops.html — HXCaine
– HXCaine, Commented May 24, 2010 at 10:09
Have a look at this question: stackoverflow.com/questions/1026761/… — David Webb
– David Webb, Commented May 24, 2010 at 10:20

reflog · Accepted Answer · 2010-05-24 10:27:42Z

27

here's the code:

public static short twoBytesToShort(byte b1, byte b2) {
          return (short) ((b1 << 8) | (b2 & 0xFF));
}

answered May 24, 2010 at 10:27

reflog

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4 Comments

Shane Over a year ago

Thats great, Thanks a million

reflog Over a year ago

@Shane, if this works for you, you should 'Accept' the answer :)

EntangledLoops Over a year ago

Why are you OR'ing the bottom byte by 0xFF?

DanielHsH Over a year ago

The &OxFF is a must!!! This is due to the fact that some Java architectures do integer promotions so if 'b2' > 127 the result will have a negative sign (highest bit of 'b2' became the sign bit since it was promoted to 32'th bit of integer). I have personally seen this happening On Android 6 devices

RedXVIIII · Accepted Answer · 2014-01-22 03:03:14Z

-1

Here's a better answer that might make a little more sense...

public static short twoBytesToShort(byte b1, byte b2) {
          return (short) ((b1 << 8) | b2);
}

(b2 & 0xFF) comes out with the same exact binary pattern.

answered Jan 22, 2014 at 3:03

RedXVIIII

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1 Comment

DanielHsH Over a year ago

That is completely wrong and might yield wrong result. The &OxFF is a must!!! This is due to the fact that some Java architectures do integer promotions so if 'b2' > 127 the result will have a negative sign (highest bit of 'b2' became the sign bit since it was promoted to 32'th bit of integer). I have personally seen this happening (On Android 6 devices)

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