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From: Malcolm McLean <malcolm.arthur.mclean@gmail.com>
Newsgroups: comp.lang.c
Subject: Re: Good hash for pointers
Date: Fri, 24 May 2024 19:57:17 +0100
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On 24/05/2024 19:28, Bonita Montero wrote:
> Am 23.05.2024 um 13:11 schrieb Malcolm McLean:
>>
>> What is a good hash function for pointers to use in portable ANSI C?
>>
>> The pointers are nodes of a tree, which are read only, and I want to 
>> associate read/write data with them. So potentially a lage number of 
>> pointers,and they might be consecutively ordered if they are taken 
>> from an array, or they might be returned from repeared calls to 
>> malloc() with small allocations. Obviously I have no control over 
>> pointer size or internal representation.
>>
> 
> Use FNV.
>

Here's an attempt.

/* FNV hash of a pointer */
static unsigned int hash(void *address)
{
     int i;
     unsigned long answer = 2166136261;
     unsigned char *byte = (unsigned char *) &address;

     for (i = 0; i < sizeof(void *); i++)
     {
         answer *= 16777619;
         answer ^= byte[i];
     }
     return (unsigned int) (answer & 0xFFFFFFFF);
}

Now what will compilers make of that?

-- 
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