Hello all, my comment said ffs(), but the code only uses fls() and that's what I meant.
Am So., 20. Jan. 2019 um 04:49 Uhr schrieb Linus Torvalds <[email protected]>: > But yes, our current int_sqrt64() does seem buggy as-is, because it's > *supposed* to work on u64's, even if I don't think we really have any > users that care. Right. No real bug, just not 100% correct code. > And as Will mentioned, the regular int_sqrt() looks perfectly fine, > and subtracting 1 from the __fls() return value would actually > _introduce_ a bug. I think no bug introduced as the code handling 0 and 1 is already done. For __fls() and fls64() I am actually using the folloing code: /* * fls - find last (most-significant) bit set * Note fls(0) = 0, fls(1) = 1, fls(0x80000000) = 32. */ static __always_inline unsigned int flsl(unsigned long x) { return x ? sizeof(x) * 8 - __builtin_clzl(x) : 0; } Please note the "_builtin_clzl()" instead of the "_builtin_clz()". The real bug is that we compute 1 to 64 for bit 0 to bit 63, whereas the algorithm expects 0 to 63 for the value of m. best regards, Florian La Roche
