RE: from where comes "__moddi3"?
On Sat, 2007-07-21 at 14:27 -0700, David Schwartz wrote: > > On 7/21/07, Jan Engelhardt <[EMAIL PROTECTED]> wrote: > > > v & 0x0F <=> v % 16 > > Indeed. (Why would anyone want to mod/div by 15 anyway?). My bad. > > Actually, it's the compiler's bad. That's a pretty fundamental equivalence > that the compiler should recognize for native integral types. for unsigned ones for sure yes... but the original question was about 15 not 16. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
RE: from where comes "__moddi3"?
> On 7/21/07, Jan Engelhardt <[EMAIL PROTECTED]> wrote: > > v & 0x0F <=> v % 16 > Indeed. (Why would anyone want to mod/div by 15 anyway?). My bad. Actually, it's the compiler's bad. That's a pretty fundamental equivalence that the compiler should recognize for native integral types. DS - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: from where comes "__moddi3"?
On Sat, 2007-07-21 at 21:58 +0200, Jan-Benedict Glaw wrote: > On Sat, 2007-07-21 21:31:13 +0200, Peter Zijlstra <[EMAIL PROTECTED]> wrote: > > On Sat, 2007-07-21 at 15:21 -0400, Robert P. J. Day wrote: > > > > use do_div(). > > > > 16 works because gcc translates that into a right shift. > > Right shift? Doesn't it just mask out everything but the low 4 bit? Yeah, its bitwise and for modulo and shifts for mult and div. Silly mistake on my side. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: from where comes "__moddi3"?
On 7/21/07, Jan Engelhardt <[EMAIL PROTECTED]> wrote: v & 0x0F <=> v % 16 Indeed. (Why would anyone want to mod/div by 15 anyway?). My bad. Regards, -- Alex - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: from where comes "__moddi3"?
On Sat, 2007-07-21 21:31:13 +0200, Peter Zijlstra <[EMAIL PROTECTED]> wrote: > On Sat, 2007-07-21 at 15:21 -0400, Robert P. J. Day wrote: > > use do_div(). > > 16 works because gcc translates that into a right shift. Right shift? Doesn't it just mask out everything but the low 4 bit? MfG, JBG -- Jan-Benedict Glaw [EMAIL PROTECTED] +49-172-7608481 Signature of: God put me on earth to accomplish a certain number of the second :things. Right now I am so far behind I will never die. signature.asc Description: Digital signature
Re: from where comes "__moddi3"?
On Sat, 21 Jul 2007, Peter Zijlstra wrote: > On Sat, 2007-07-21 at 15:21 -0400, Robert P. J. Day wrote: > > again, probably displaying my abject ignorance, but i wrote a > > trivial module that tries to "var % 15", and i get: > > > > WARNING: "__moddi3" undefined! > > > > and, not surprisingly, when i try to insmod: > > > > insmod: error inserting 'seq.ko': -1 Unknown symbol in module > > > > (using 16 rather than 15 works fine, as i assume that the modulus > > call is simply replaced by an optimized bitwise comparison.) > > > > so ... from where comes __moddi3? i know there are places in the > > kernel source tree that do non-power-of-2 moduli, and they work fine, > > no? thanks. > > let me guess, 32 bit kernel, and var is 64 bit? um ... yeah. duh. var type is actually loff_t. i should have realized that. > gcc translates that into a libgcc call, which we _explicitly_ do not > have because 64bit divisions are expensive! > > use do_div(). gotcha. thanks. rday -- Robert P. J. Day Linux Consulting, Training and Annoying Kernel Pedantry Waterloo, Ontario, CANADA http://fsdev.net/wiki/index.php?title=Main_Page - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: from where comes "__moddi3"?
On Jul 21 2007 23:33, Alexander Shishkin wrote: > On 7/21/07, Robert P. J. Day <[EMAIL PROTECTED]> wrote: >> >> again, probably displaying my abject ignorance, but i wrote a >> trivial module that tries to "var % 15", and i get: >> >> WARNING: "__moddi3" undefined! > ...which comes from libgcc1 which you obviously don't want to link against. > > Does (var & 0x0f) not work for you? v & 0x0F <=> v % 16 Jan -- - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: from where comes "__moddi3"?
On 7/21/07, Robert P. J. Day <[EMAIL PROTECTED]> wrote: again, probably displaying my abject ignorance, but i wrote a trivial module that tries to "var % 15", and i get: WARNING: "__moddi3" undefined! ...which comes from libgcc1 which you obviously don't want to link against. Does (var & 0x0f) not work for you? Regards, -- Alex - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: from where comes "__moddi3"?
On Sat, 2007-07-21 at 15:21 -0400, Robert P. J. Day wrote: > again, probably displaying my abject ignorance, but i wrote a > trivial module that tries to "var % 15", and i get: > > WARNING: "__moddi3" undefined! > > and, not surprisingly, when i try to insmod: > > insmod: error inserting 'seq.ko': -1 Unknown symbol in module > > (using 16 rather than 15 works fine, as i assume that the modulus > call is simply replaced by an optimized bitwise comparison.) > > so ... from where comes __moddi3? i know there are places in the > kernel source tree that do non-power-of-2 moduli, and they work fine, > no? thanks. let me guess, 32 bit kernel, and var is 64 bit? gcc translates that into a libgcc call, which we _explicitly_ do not have because 64bit divisions are expensive! use do_div(). 16 works because gcc translates that into a right shift. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
