Aleksandar Markovic 3ec404d88c MIPS: math-emu: RINT.<D|S>: Fix several problems by reimplementation ... Reimplement RINT.<D|S> kernel emulation so that all RINT.<D|S> specifications are met. For the sake of simplicity, let's analyze RINT.S only. Prior to this patch, RINT.S emulation was essentially implemented as (in pseudocode) <output> = ieee754sp_flong(ieee754sp_tlong(<input>)), where ieee754sp_tlong() and ieee754sp_flong() are functions providing conversion from double to integer, and from integer to double, respectively. On surface, this implementation looks correct, but actually fails in many cases. Following problems were detected: 1. NaN and infinity cases will not be handled properly. The function ieee754sp_flong() never returns NaN nor infinity. 2. For RINT.S, for all inputs larger than LONG_MAX, and smaller than FLT_MAX, the result will be wrong, and the overflow exception will be erroneously set. A similar problem for negative inputs exists as well. 3. For some rounding modes, for some negative inputs close to zero, the return value will be zero, and should be -zero. This is because ieee754sp_flong() never returns -zero. This patch removes the problems above by implementing dedicated functions for RINT.<D|S> emulation. The core of the new function functionality is adapted version of the core of the function ieee754sp_tlong(). However, there are many details that are implemented to match RINT.<D|S> specification. It should be said that the functionality of ieee754sp_tlong() actually closely corresponds to CVT.L.S instruction, and it is used while emulating CVT.L.S. However, RINT.S and CVT.L.S instructions differ in many aspects. This patch fulfills missing support for RINT.<D|S>. Signed-off-by: Miodrag Dinic <miodrag.dinic@imgtec.com> Signed-off-by: Goran Ferenc <goran.ferenc@imgtec.com> Signed-off-by: Aleksandar Markovic <aleksandar.markovic@imgtec.com> Cc: David S. Miller <davem@davemloft.net> Cc: Douglas Leung <douglas.leung@imgtec.com> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Hans Verkuil <hans.verkuil@cisco.com> Cc: James Hogan <james.hogan@imgtec.com> Cc: Maciej W. Rozycki <macro@imgtec.com> Cc: Masahiro Yamada <yamada.masahiro@socionext.com> Cc: Mauro Carvalho Chehab <mchehab@kernel.org> Cc: Paul Burton <paul.burton@imgtec.com> Cc: Petar Jovanovic <petar.jovanovic@imgtec.com> Cc: Raghu Gandham <raghu.gandham@imgtec.com> Cc: Randy Dunlap <rdunlap@infradead.org> Cc: linux-mips@linux-mips.org Cc: linux-kernel@vger.kernel.org Patchwork: https://patchwork.linux-mips.org/patch/17141/ Signed-off-by: Ralf Baechle <ralf@linux-mips.org>		2017-08-29 15:21:56 +02:00
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mips	MIPS: math-emu: RINT.<D|S>: Fix several problems by reimplementation	2017-08-29 15:21:56 +02:00
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