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From: "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com>
Newsgroups: comp.lang.c
Subject: Re: Good hash for pointers
Date: Fri, 24 May 2024 10:51:45 -0700
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On 5/24/2024 10:49 AM, Chris M. Thomasson wrote:
> On 5/24/2024 4:05 AM, Malcolm McLean wrote:
> [...]
>> 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 this out, it relies on hashing pointers, the multex... ;^)
> 
> https://groups.google.com/g/comp.lang.c++/c/sV4WC_cBb9Q/m/SkSqpSxGCAAJ
> 
> It can be used for many different things...
> 
> 

The naive hash is:
______________________
// A table of locks
struct mutex_table
{
   std::vector<std::mutex> m_locks;

   mutex_table(std::size_t size) : m_locks(size) { assert(size > 0); }

   // totally contrived simple hash...
   std::size_t hash(void const* ptr)
   {
     std::uintptr_t ptr_uint = (std::uintptr_t)ptr;
     return (std::size_t)(((ptr_uint << 9) * 103) % m_locks.size());
   }
};
______________________

;^)