BUG #6460: routine my_log2 use incorrect data type ?

The following bug has been logged on the website:

Bug reference: 6460
Logged by: lxzou
Email address: zoulx1982(at)163(dot)com
PostgreSQL version: 9.1.2
Operating system: Windows Server 2008 64 bit
Description:

Hi,
I startup postgres in win server 2008 64-bit with
shared_buffers=1073741819, but find it doesn't work.

I debug the postgres use vs2008, and find it enter an Infinite loop in
my_log2.

when the parameter num is between (2^30) + 1 and (2^31) -1, it will be an
Infinite loop.

because long in win 64 is 4 bytes, so (2^30) << 1 is 2^31, i.e. -2^31.
move left again it will be zero.

size_t in win64 is 8 bytes，so add_size and mul_size can't check overflow,
but in win32 it can do that.

So, whether we should use Size instead of long ?

Best wishes