left shift operator/function

Community Support
1

Hello:
    I’m not able to find a left/right shift operator like in C: 8 >>  1 = 4.

I can use div 2, 4 8  etc. But is there a shift function/operator?

Thanks in advance.

2

Hi

You can achieve shifting using vs/sv and prev/next. In example below x is the number of shifts and y is the starting number:

q){0b sv prev/[x;0b vs y]}[1;8]

4

“0b vs” will convert a number to its binary representation, “0b sv” is the reverse operation:

q)0b vs 8

0000000000000000000000000000000000000000000000000000000000001000b

q)0b sv 0b vs 8

8

The operators prev and next will move the sequence:

q)next 0b vs 8

0000000000000000000000000000000000000000000000000000000000010000b

q)prev 0b vs 8

0000000000000000000000000000000000000000000000000000000000000100b

Hope this helps.

Thomas Smyth

AquaQ Analytics

3

Thanks Thomas.
I don’t know sv can be used on numbers before.

Meanwhile, I find a solution based on integer multiple and division.

lshift: { x * prd y # 2 }   

rshift: { x div prd y # 2 } 

Also I’m wondering why this operator is not provided by kdb+, given that there is a x86 assembly instruction for it.

Regards

Hao