C:\test\C>gcm
anonyM: gcm for  s=2147483648 & r=1 to 1073741824 took:8.535316994670
anonyM: gcm2 for s=2147483648 & r=1 to 1073741824 took:2.271266720696

##</code><code>##

U64 gcm2( U64 max, U64 lcm ) {
    I32 b;

    _BitScanForward64( &b, lcm & 0xfff );
    lcm <<= ( 12 - b );
    return ( max / lcm ) * lcm;
}