From: Jonathan Kimmitt <jonathan@kimmitt.co.uk>
To: caml-list@yquem.inria.fr
Subject: Re: optimize div to right shift (NOT!)
Date: Mon, 13 Dec 2010 12:33:33 +0000 [thread overview]
Message-ID: <BB6FC70B-2E26-4BD2-8335-FB31E90FA377@kimmitt.co.uk> (raw)
In-Reply-To: <20101212172643.3EF80BC5D@yquem.inria.fr>
> A C compiler would optimize this to a right shift. Changing that to 'Int64.shift_right n 1' speeds
> up the code.
Sorry to be a pedant, but this is not correct. The optimisation is only possible when the arguments
are unsigned integers which I don't think is specifiable when working in OCAML
# Int64.shift_right (-2L) 1;;
- : int64 = -1L (So far, so good)
# Int64.div (-1L) 2L;;
- : int64 = 0L (Good)
# Int64.shift_right (-1L) 1;;
- : int64 = -1L (Duh)
next parent reply other threads:[~2010-12-13 12:33 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20101212172643.3EF80BC5D@yquem.inria.fr>
2010-12-13 12:33 ` Jonathan Kimmitt [this message]
2010-12-13 12:58 ` [Caml-list] " Török Edwin
2010-12-13 13:03 ` Benedikt Meurer
2010-12-13 20:13 ` Jon Harrop
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