java中的“>>>”是什么意思？

Question

im trying to translate this code to python, but im having a hard time doing so, don't worry about the index values and variable names, I just want to know what the ">>>" part does exactly, perhaps a python equivalent, but an explanation would be great:

target[0] = (char)(source[sourceIndex] >>> 2);
target[1] = (char)((source[sourceIndex] & 3) << 4 | source[sourceIndex + 1] >>> 4);
target[2] = (char)((source[sourceIndex + 1] & 0xf) << 2 | source[sourceIndex + 2] >>> 6);
target[3] = (char)(source[sourceIndex + 2] & 0x3f);

Any help would be appreciated

Answer 1

The "<<<" and ">>" are bit shift operators. Specifically,

The signed left shift operator "<<" shifts a bit pattern to the left, and the signed right shift operator ">>" shifts a bit pattern to the right. The bit pattern is given by the left-hand operand, and the number of positions to shift by the right-hand operand. The unsigned right shift operator ">>>" shifts a zero into the leftmost position, while the leftmost position after ">>" depends on sign extension.

—— from The Java™ Tutorials - Bitwise and Bit Shift Operators

Answer 2

It's an "unsigned right shift".

So, if your number ( x ) is 11110000 (in binary).

x >>> 1 will be 01111000 (in binary).

This is opposed to x >> 1 which will result in 11111000 (in binary).

The >> tries to preserve the "sign bit" but the >>> does not.

Note: I've assumed a 8-bit integer (or a byte in Java). The same thing holds for 2-byte and 4-byte integers.

Answer 3

Thats the unsigned right shift operator. It's a bitwise operator that shifts a zero into the leftmost bit of your operand. Here - http://docs.oracle.com/javase/tutorial/java/nutsandbolts/op3.html .