On Tue, 2021-08-17 at 14:04:26 -0700, Paul Eggert wrote:
> On 8/17/21 3:32 AM, Jim Meyering wrote: >> - size_t h = 0; >> + size_t h = 5381; > > I expect DJB chose that number because of the primeth recurrence sequence > <https://oeis.org/A007097>: > > 2 is 1st prime. > 3 is 2nd prime. > 5 is 3rd prime. > 11 is 5th prime. > 31 is 11th prime. > 127 is 31st prime. > 709 is 127th prime. > 5381 is 709th prime. > 52711 is 5381st prime. > ... > > Although 5381 is the largest number in this sequence that can fit into > 'int' in a portable C program, and that's probably why DJB chose 5381, > we're not limited to such small values here. > > How about the attached patch instead? > How about letting the compiler choose which prime to use? - something like the following: #define H15_PRIME (unsigned long long)5381 #define H32_PRIME (unsigned long long)3657500101 #define H64_PRIME (unsigned long long)4123221751654370051 size_t h = H64_PRIME <= SIZE_MAX ? H64_PRIME : H32_PRIME <= SIZE_MAX ? H32_PRIME : H15_PRIME;
