Syntax/operators Java - What does this line mean?

Question

I've found one line in Java like this :

result |= (b & 0x1f) << shift;

I've searched about what operators do but I'm still not able to understand what it is supposed to do assuming result, b and shift are integer values.
Could anyone tell me what does this line is supposed to do ?

Update - Here is the sample part of the code found here

int b, shift = 0, result = 0;
do {
    b = encoded.charAt(index++) - 63;
    result |= (b & 0x1f) << shift;
    shift += 5;
} while (b >= 0x20);

You need to provide more context to learn what this is doing. Is the code from here: http://jeffreysambells.com/2010/05/27/decoding-polylines-from-google-maps-direction-api-with-java — Adam Burry, Aug 26 '13 at 15:14
possible duplicate of [What does "|=" mean in Java?](http://stackoverflow.com/questions/3420925/what-does-mean-in-java) — Zavior, Aug 26 '13 at 15:15
If you know what `&`, `<<` and `|=` does, you should be able to understand what that line does. — Bernhard Barker, Aug 26 '13 at 15:22
@Adam Burry updated. @Dukeling Yes, of course, I can't get that part in particular : `(b & 0x1f) << shift` even if I have basic knowledge in hexadecimal values and shift operator. — Sw4Tish, Aug 26 '13 at 15:23

score 5 · Accepted Answer · answered Aug 26 '13 at 15:34

Maybe this explanation might help you:

A. (b & 0x1f): performs a logical AND operation between b and 0xf1. This means: return the last 5 bits of b

B. A << shift: shifts to the left an amount of shift bits the result of A operation. This means: shift the last 5 bits of b an amount of shift bits to the left.

C. result |= B: assigns to result variable the result of perform a logical OR operation between result itself and the result of B operation. This means: perform a logical OR between result and the last 5 bits of b shifted to the left an amount of shift bits, and then assign the result to result variable.

Hope it be understandable.

score 2 · Answer 2 · edited Jan 30 '17 at 14:41

2

It preserves the last 5 bits of b, left shifts them some amount and ors them into result.

In this case it is reversing the process described here: https://developers.google.com/maps/documentation/utilities/polylinealgorithm

edited Jan 30 '17 at 14:41

andriy

4,074
9
44
71

answered Aug 26 '13 at 15:13

Adam Burry

1,904
13
20

Thanks for the documentation ! – Sw4Tish Aug 26 '13 at 15:34

Syntax/operators Java - What does this line mean?

2 Answers2