On Mon, Sep 7, 2015 at 6:03 PM, Ted Unangst <t...@tedunangst.com> wrote: > Michael Warmuth-Uhl wrote: >> On 2015-09-07, Otto Moerbeek wrote: >> It seems to fix the issues on amd64, but I'm not sure if the accuracy of >> long double and sqrtl is guaranteed to be enough in general. > > using floating point seems suspect. i think what's needed is an integer sqrt > function.
Floating point works fine for integers as long as your integers fit within the mantissa component of the floating point representation. Assuming the usual IEEE-754 implementation: For double, this means integers cannot exceed 2^53 (9007199254740992) without losing least significant bits (2^53-1 can be represented, 2^53 can be represented but has lost the least significant bit so typically that means it's assumed to be zero - which is fine, but that means that 1+2^53 cannot be represented). For long double, this means integers cannot exceed 2^113 (10384593717069655257060992658440192) without losing least significant bits. That said, you can implement integer square root using binary search. -- Raul
