On Jun 1, 2011, at 11:34 AM, Roy Stogner wrote: > > On Wed, 1 Jun 2011, Cody Permann wrote: > >> We (the INL) have the need to grow the number of subdomains in our >> simulations past the current storage capacity of subdomain_id_type. >> This type is currently set as an unsigned char allowing only 256 >> subdomains. We are already starting to run and debug libMesh using >> a locally patched version allowing a storage size of 16 bits. I >> wanted to see what thoughts the other developers have to growing >> this type permanently to 16 bits. Should we make a new configure >> option to allow us to change the default size? Should we just make >> the change to the library? > > My personal preference would be to have it default to 8 bits, but > configurable to 16 bits with --enable-16bit-subdomain-ids and/or > --enable-everything. Default to 16 bits but configurable to > --enable-8bit-subdomain-ids would be fine if enough people disagree > with me. > > If you're futzing around with configuring data sizes and want to make > processor_id_type configure-time expandable that might be nice too. > >> Are there other issues/concerns with changing this type? > > I'm pretty sure we'll break if it goes above 32 bits. (but it > actually might work at 32 bits too, if you want to add a non-default > option for that) > > Struct padding in elem.h is such that adding 1 byte to > sizeof(subdomain_id_type) won't necessarily add 1 byte to > sizeof(Elem). At first glance it looks like it would add 4 bytes on > 32-bit systems or 0 bytes on 64-bit systems, but I wouldn't swear to > any of that.
Yes I came to the exact same conclusion based on what I know about struct padding. I just verified on my 64-bit Mac that changing the subdomain size to 16 bits did _NOT_ change the overall size of an element. (HEX8 is 96 bytes before and after on this system) > --- > Roy ------------------------------------------------------------------------------ Simplify data backup and recovery for your virtual environment with vRanger. Installation's a snap, and flexible recovery options mean your data is safe, secure and there when you need it. Data protection magic? Nope - It's vRanger. Get your free trial download today. http://p.sf.net/sfu/quest-sfdev2dev _______________________________________________ Libmesh-devel mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/libmesh-devel
