From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Original-To: caml-list@yquem.inria.fr Delivered-To: caml-list@yquem.inria.fr Received: from mail3-relais-sop.national.inria.fr (mail3-relais-sop.national.inria.fr [192.134.164.104]) by yquem.inria.fr (Postfix) with ESMTP id 85F2EBC37 for ; Wed, 28 Oct 2009 14:57:42 +0100 (CET) X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: AgcDAIvq50rZSMDqi2dsb2JhbACBT5lwAQEBCgsKBxEFvkeEPwSBYQ X-IronPort-AV: E=Sophos;i="4.44,640,1249250400"; d="scan'208";a="37142078" Received: from fmmailgate03.web.de ([217.72.192.234]) by mail3-smtp-sop.national.inria.fr with ESMTP; 28 Oct 2009 14:57:42 +0100 Received: from smtp06.web.de (fmsmtp06.dlan.cinetic.de [172.20.5.172]) by fmmailgate03.web.de (Postfix) with ESMTP id B75C412BDFF0F for ; Wed, 28 Oct 2009 14:54:40 +0100 (CET) Received: from [95.208.117.111] (helo=frosties.localdomain) by smtp06.web.de with asmtp (TLSv1:AES256-SHA:256) (WEB.DE 4.110 #314) id 1N38z2-0006ud-00 for caml-list@inria.fr; Wed, 28 Oct 2009 14:54:40 +0100 Received: from mrvn by frosties.localdomain with local (Exim 4.69) (envelope-from ) id 1N38z2-00071o-4z for caml-list@inria.fr; Wed, 28 Oct 2009 14:54:40 +0100 From: Goswin von Brederlow To: caml-list@inria.fr Subject: How to read different ints from a Bigarray? Date: Wed, 28 Oct 2009 14:54:40 +0100 Message-ID: <87eiond3of.fsf@frosties.localdomain> User-Agent: Gnus/5.110006 (No Gnus v0.6) XEmacs/21.4.22 (linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: goswin-v-b@web.de X-Sender: goswin-v-b@web.de X-Provags-ID: V01U2FsdGVkX1/5a1zIyjYTzK4/jtAxvYNkOp/7R3IAW7TlnYDd 6MOsDyum8OQOx2+kIJiWJakItK2LyWxAw9n6qMrqbsO8D5Dkpn VyXG/KyoI= X-Spam: no; 0.00; bigarray:01 buffer:01 elt:01 bigarray:01 buf:01 buf:01 elt:01 endian:01 byte:01 endian:01 elegantly:01 stubs:01 blit:01 memcpy:01 mfg:98 Hi, I'm working on binding s for linux libaio library (asynchron IO) with a sharp eye on efficiency. That means no copying must be done on the data, which in turn means I can not use string as buffer type. The best type for this seems to be a (int, int8_unsigned_elt, c_layout) Bigarray.Array1.t. So far so good. Now I define helper functions: let get_uint8 buf off = buf.{off} let set_uint8 buf off x = buf.{off} <- x But I want more: get/set_int8 - do I use Obj.magic to "convert" to int8_signed_elt? And endian correcting access for larger ints: get/set_big_uint16 get/set_big_int16 get/set_little_uint16 get/set_little_int16 get/set_big_uint24 ... get/set_little_int56 get/set_big_int64 get/set_little_int64 What is the best way there? For uintXX I can get_uint8 each byte and shift and add them together. But that feels inefficient as each access will range check and the shifting generates a lot of code while cpus can usualy endian correct an int more elegantly. Is it worth the overhead of calling a C function to write optimized stubs for this? And last: get/set_string, blit_from/to_string Do I create a string where needed and then loop over every char calling s.(i) <- char_of_int buf.{off+i}? Or better a C function using memcpy? What do you think? MfG Goswin PS: Does batteries have a better module for this than Bigarray?