Is there a way to get the first active bit through SQL (MySQL)?

I have a column named a, and a column named b.

I want to fill with an UPDATE ... SET b = ... query the b column, so that it contains the first bit 开发者_开发百科that a has set to 1. Okay, you probably didn't understand, it's much easier to understand with an example:

a = 2508 = 0x9CC = 0100111001100  
b = 4    = 0x4   = 0000000000100

a = 2080 = 0x820 = 0100000100000  
b = 32   = 0x20  = 0000000100000

Is there a way to do this in pure SQL?

This should do it:

update your_table
set b = if(a > 0,pow(2,instr(reverse(bin(a)),'1')-1),0);