Sujet : Re: Good hash for pointers
De : malcolm.arthur.mclean (at) *nospam* gmail.com (Malcolm McLean)
Groupes : comp.lang.cDate : 24. May 2024, 15:07:28
Autres entêtes
Organisation : A noiseless patient Spider
Message-ID : <v2q6v0$2br8t$1@dont-email.me>
References : 1 2 3 4 5 6 7 8
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On 24/05/2024 14:18, Tim Rentsch wrote:
bart <bc@freeuk.com> writes:
On 24/05/2024 02:39, Tim Rentsch wrote:
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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.
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I assume the C89 implementation is one that can target current 64
bit machines.
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Then char, short, int, long long will almost certainly have widths
of 8, 16, 32 and 64 bits respectively.
C89 doesn't have long long.
(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.
What he said was C89. He didn't mention stdint.h. I take
him at his word. If what he wants is something different,
he should say clearly what it is, and not make people guess
about it. (To be clear this recommendation is intended for
every questioner, not just Malcolm.)
cJSON.c is C89. And these additions to the resource compiler were inspired by a menntion of cJSON.c here.
So a C89 hash for a pointer to an unsigned int would be ideal. However it might be impossible to write one which is both efficient in terms of machine instructions and a good hash function in that it distributes the hashes evenly given an uneven distribution of keys. And pointers returned from repeated calls to malloc() are going to have an odd distribution of values.
-- Check out Basic Algorithms and my other books:https://www.lulu.com/spotlight/bgy1mm
Good hash for pointers
Re: Good hash for pointers