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>   >      syn = cia->cia_syn & 0xff; > -    if (syn == (syn & -syn)) { > +    if (syn == ffs_val(syn)) { >          fmt = KERN_CRIT "  ECC syndrome %#x -- check bit %d\n"; >          i = ffs(syn) - 1; >      } else { This is a check for multiple bits set, which has a simpler expression to calculate.  (the ffs() in context shows that syn isn't expected to be 0.) In Xen I added this helper while tiding things up, and it's applicable to the more common pattern of checking hweight() of a bitmap against 1. /*  * Calculate if a value has two or more bits set.  Always use this in  * preference to an expression of the form 'hweight(x) > 1'.  */ #define multiple_bits_set(x)                    \     ({                                          \         typeof(x) _v = (x);                     \         (_v & (_v - 1)) != 0;                   \     }) ~Andrew