wrong implementation of __mulhi3

[amaneureka]

This is current implementation in code base:

if a is an even integer or any integer with 0s at lower significant followed by 1s. then it will end up in an infinite loop.

Correct code should be

while(a)
{
    if (a & 1) r += b;
    b <<= 1;
    a >>= 1;
}