Re: [PATCH v3 03/22] host-utils: introduce uabs64()
On 10/21/21 3:34 PM, Eduardo Habkost wrote: On Thu, Oct 21, 2021 at 4:04 PM Richard Henderson wrote: On 9/10/21 4:26 AM, Luis Pires wrote: Introduce uabs64(), a function that returns the absolute value of a 64-bit int as an unsigned value. This avoids the undefined behavior for common abs implementations, where abs of the most negative value is undefined. I do question the comment there wrt undefined. We compile with -fwrapv, which means that *no* overflow is undefined; we always have properly truncated twos-compliment values. Can we really assume that -fwrapv would make llabs(LLONG_MIN) not undefined? We would be calling a function compiled by somebody else (possibly without -fwrapv). Fair enough. r~
Re: [PATCH v3 03/22] host-utils: introduce uabs64()
On Thu, Oct 21, 2021 at 4:04 PM Richard Henderson wrote: > > On 9/10/21 4:26 AM, Luis Pires wrote: > > Introduce uabs64(), a function that returns the absolute value of > > a 64-bit int as an unsigned value. This avoids the undefined behavior > > for common abs implementations, where abs of the most negative value is > > undefined. > > I do question the comment there wrt undefined. We compile with -fwrapv, which > means that > *no* overflow is undefined; we always have properly truncated twos-compliment > values. Can we really assume that -fwrapv would make llabs(LLONG_MIN) not undefined? We would be calling a function compiled by somebody else (possibly without -fwrapv). -- Eduardo
Re: [PATCH v3 03/22] host-utils: introduce uabs64()
On 9/10/21 4:26 AM, Luis Pires wrote: Introduce uabs64(), a function that returns the absolute value of a 64-bit int as an unsigned value. This avoids the undefined behavior for common abs implementations, where abs of the most negative value is undefined. I do question the comment there wrt undefined. We compile with -fwrapv, which means that *no* overflow is undefined; we always have properly truncated twos-compliment values. r~
