On Sat, 28 Jan 2023 at 12:15, Tom Lane <t...@sss.pgh.pa.us> wrote: > /* > * Determine the net effect of two direction specifications. > * This relies on having ForwardScanDirection = +1, BackwardScanDirection = > -1, > * and will probably not do what you want if applied to any other values. > */ > #define CombineScanDirections(a, b) ((a) * (b)) > > The main thing this'd buy us is being able to grep for uses of the > trick. If it's written as just multiplication, good luck being > able to find what's depending on that, should you ever need to.
Yeah, I think the multiplication macro is a good way of doing it. Having the definition of it close to the ScanDirection enum's definition is likely a very good idea so that anyone adjusting the enum values is more likely to notice that it'll cause an issue. A small note on the enum declaration about the -1, +1 values being exploited in various places might be a good idea too. I see v6-0006 in [1] further exploits this, so that's further reason to document that. My personal preference would have been to call it ScanDirectionCombine, so the naming is more aligned to the 4 other macro names that start with ScanDirection in sdir.h, but I'm not going to fuss over it. David [1] https://postgr.es/m/caakru_zyixwws1wxszneoy+sjoh_+f5uho-1ufhyi-u0d6z...@mail.gmail.com David
