Sujet : Re: Good hash for pointers
De : malcolm.arthur.mclean (at) *nospam* gmail.com (Malcolm McLean)
Groupes : comp.lang.cDate : 24. May 2024, 12:05:19
Autres entêtes
Organisation : A noiseless patient Spider
Message-ID : <v2ps9g$29v2e$1@dont-email.me>
References : 1 2 3 4 5 6 7
User-Agent : Mozilla Thunderbird
On 24/05/2024 11:14, bart wrote:
On 24/05/2024 02:39, Tim Rentsch wrote:
Malcolm McLean <malcolm.arthur.mclean@gmail.com> writes:
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On 24/05/2024 00:52, Tim Rentsch wrote:
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Malcolm McLean <malcolm.arthur.mclean@gmail.com> writes:
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On 23/05/2024 23:49, Tim Rentsch wrote:
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Malcolm McLean <malcolm.arthur.mclean@gmail.com> writes:
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What is a good hash function for pointers to use in portable
ANSI C?
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I have a preliminary question. Do you really mean ANSI C, or
is C99 acceptable?
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C89 is better.
But the pass has been sold.
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I'm not asking which you think is better. I'm asking about
what your requirements are.
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C 89.
I don't want to pull in C99 types and so on just for a hash function.
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In that case I think you are stuck with using a half-baked
solution. The standard integer types available in C89 just
aren't a good fit in a 64-bit world.
I assume the C89 implementation is one that can target current 64 bit machines.
Then char, short, int, long long will almost certainly have widths of 8, 16, 32 and 64 bits respectively.
(I don't know if 'long long' was part of C89, but it sounds like Malcolm just doesn't want to be bothered with stdint.h, and any compiler used is like to support it.
I can't stand it either. Just today I wrote these two lines:
typedef unsigned long long u64;
typedef unsigned char byte;
to avoid stdint.h and its ugly set of types.)
The code is very clean.
And it seems I've got to introduce a lot of ugliness for an efficent hash function. But pointers will of course be in registers, and the hash index should also be in a register. And the hash lookup is in the inner loop, and it is called for every node in the xml document which is visited. So the hash function should be an all register, inline function.
Then I can't be the first person to want to use a pointer as a key for hash table.
And I don't want things to break if pointer representation changes.
-- Check out Basic Algorithms and my other books:https://www.lulu.com/spotlight/bgy1mm
Good hash for pointers
Re: Good hash for pointers