I referred to SoftFloat library in QEMU code, and the case "Operand is smaller than INT_MIN" is different between SoftFloat and Mips-B, while the case "Operand is a NaN" is different between SoftFloat and Mips-A.
Aleksandar ________________________________________ From: Maciej Rozycki Sent: Tuesday, June 07, 2016 4:39 AM To: Aleksandar Markovic Cc: qemu-devel@nongnu.org; peter.mayd...@linaro.org; pro...@gmail.com; kbast...@mail.uni-paderborn.de; mark.cave-ayl...@ilande.co.uk; ag...@suse.de; blauwir...@gmail.com; jcmvb...@gmail.com; Aleksandar Markovic; qemu-...@nongnu.org; qemu-...@nongnu.org; Petar Jovanovic; pbonz...@redhat.com; Miodrag Dinic; edgar.igles...@gmail.com; g...@mprc.pku.edu.cn; Leon Alrae; afaer...@suse.de; Aurelien Jarno; r...@twiddle.net Subject: Re: [PATCH v6 8/9] target-mips: Add nan2008 flavor of <CEIL|CVT|FLOOR|ROUND|TRUNC>.<L|W>.<S|D> On Mon, 16 May 2016, Aleksandar Markovic wrote: > Here one can distinguish three cases: > > CASE MIPS-A: (FCR31.NAN2008 == 1) > > 1. Operand is a NaN, result should be 0; > 2. Operand is larger than INT_MAX, result should be INT_MAX; > 2. Operand is smaller than INT_MIN, result should be INT_MIN. > > CASE MIPS-B: (FCR31.NAN2008 == 0) > > 1. Operand is a NaN, result should be INT_MAX; > 2. Operand is larger than INT_MAX, result should be INT_MAX; > 2. Operand is smaller than INT_MIN, result should be INT_MAX. > > CASE SOFTFLOAT: > > 1. Operand is a NaN, result is INT_MAX; > 2. Operand is larger than INT_MAX, result is INT_MAX; > 2. Operand is smaller than INT_MIN, result is INT_MIN. > > It is interesting that neither MIPS-A nor MIPS-B desired behaviors > are in this sense identical to correspondent SoftFloat behavior. A bug in SoftFloat probably -- it has only been fixed quite recently to handle all MIPS architecture's peculiarites correctly and this case must have been missed then, making data produced not necessarily identical between the legacy-NaN hard-float and the soft-float ABIs, even though intent has been for it to be. FAOD, you refer to SoftFloat in the most recent version of GCC, do you? Maciej
