GNU bug report logs - #50093
djb2 correction

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Message #19 received at 50093-done <at> debbugs.gnu.org (full text, mbox):

From: Paul Eggert <eggert <at> cs.ucla.edu>
To: alex.murray <at> canonical.com
Cc: Jim Meyering <jim <at> meyering.net>, 50093-done <at> debbugs.gnu.org
Subject: Re: bug#50093: djb2 correction
Date: Wed, 18 Aug 2021 07:48:09 -0700

On 8/17/21 7:50 PM, Alex Murray wrote:
> 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;

That's equivalent to the patch I suggested; on my platform it even 
generates the same machine code. It's better to avoid macros when that's 
easy, as is the case here.

I installed the patch, except with uint_fast64_t instead of unsigned 
long long int as that's a better type for the 64-bit constants in 
question. (In case you're wondering what that "_fast" is doing there, 
POSIX and the C standard guarantee the existence of uint_fast64_t but 
not of uint64_t, as a concession to Unisys mainframes where long long is 
72 bits.)

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