From: Martin Jambon <martin.jambon@ens-lyon.org>
To: Xavier Leroy <xavier.leroy@inria.fr>
Cc: caml-list@inria.fr
Subject: Re: [Caml-list] Hashing failure
Date: Fri, 21 Dec 2012 11:03:13 -0800 [thread overview]
Message-ID: <50D4B271.7030209@ens-lyon.org> (raw)
In-Reply-To: <50D433BE.4010309@inria.fr>
On Fri 21 Dec 2012 02:02:38 AM PST, Xavier Leroy wrote:
> On 12/20/2012 09:18 PM, Thomas Braibant wrote:
>
>> [Reducing a hash value to a [0, N) interval ]
>> My question is : is there a safe way to bullet-proof my code against
>> these pathological cases, without too much hinderance (this is some
>> code whose efficiency is critical...)
>
> Some possibilities to reduce an integer k to the interval [0, N):
>
> abs (k mod N)
> (if N > 0, k mod N is guaranteed to be in (-N,N) )
>
> (k land max_int) mod N
> ("land max_int" masks the sign bit off and preserves all other
> bits, reducing k to [0, max_int])
Is the two's complement representation of integers guaranteed by all
OCaml implementations? It would be helpful if the manual was explicit
about it.
Martin
prev parent reply other threads:[~2012-12-21 19:03 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <CAHR=VkzBhR5FMsWO-_BVzYV4yhSARP8rg7G3b=jezU6OOOg0jQ@mail.gmail.com>
2012-12-20 20:18 ` Thomas Braibant
2012-12-20 20:32 ` [Caml-list] " Thomas Braibant
2012-12-20 21:01 ` Martin Jambon
2012-12-21 7:58 ` [Caml-list] " Jacques Garrigue
2012-12-21 10:02 ` Xavier Leroy
2012-12-21 19:03 ` Martin Jambon [this message]
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