From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 33387D70DEB for ; Thu, 28 Nov 2024 18:14:03 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1tGj0u-0000nm-FA; Thu, 28 Nov 2024 13:13:16 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1tGj0p-0000nJ-3h for qemu-devel@nongnu.org; Thu, 28 Nov 2024 13:13:12 -0500 Received: from mail-oo1-xc34.google.com ([2607:f8b0:4864:20::c34]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.90_1) (envelope-from ) id 1tGj0n-0007YV-Hj for qemu-devel@nongnu.org; Thu, 28 Nov 2024 13:13:10 -0500 Received: by mail-oo1-xc34.google.com with SMTP id 006d021491bc7-5ee9dbf1b47so1003527eaf.1 for ; Thu, 28 Nov 2024 10:13:08 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; t=1732817588; x=1733422388; darn=nongnu.org; h=content-transfer-encoding:in-reply-to:from:content-language :references:to:subject:user-agent:mime-version:date:message-id:from :to:cc:subject:date:message-id:reply-to; bh=HWVhMHKiHIZ4cMOKLHT1DDD/tII1X73lG8ZIYKCTD58=; b=L36NMelMDLb/iZYFokdCOVPHP3kl6JQLP+ukPttbVyKjXxMZDCyoNrc+mODK5BqT0F rVWeKlI8VnGkiQDGroXefXYFl5oxbSfje8zDKE/hktsT/FzOPkyaDmIsXlSu7BBzfIKv TxDjBjji8VsRjmbo2fsRgN5rgnngFa4wiSy2SAh8zNcDPe+UWAhUASmklfUQXGNd5ACz 5ax8wx5rBywx+QlYKcIcg+zWYGEVrqdvx1/gJXmrCfPiYLSd2awQ/q1ujzugdSYZYX5W m6gwSDlvTpilNfUH3nnRFmcZPHdQNJt49q1Uy31E1h4fQYbFS1ZE1+ewnWMyvkwVnZOB hE7A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1732817588; x=1733422388; h=content-transfer-encoding:in-reply-to:from:content-language :references:to:subject:user-agent:mime-version:date:message-id :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=HWVhMHKiHIZ4cMOKLHT1DDD/tII1X73lG8ZIYKCTD58=; b=hOErQzuIc18rCUGzOabymisV7S9S1fTaA3lxGrrYkCLfs1L71e5mc5GqN7On6OT6cH xeHYNrsOIabRkl2P3nqGDv9WkDzmoaHvnYkDrRWDinKEyNRvryNtBkzpEbql6Fu/VWn9 FdSlI2pipGX9bWlQ58lpxAyF5wNt0/mwAkowPC2R9aMsHN91vqd9L1hQM7FwDksjydcz +QA+SiZWgC0CyqBxGRkDum4Pft4S+28M4Sm8KfHAV+U86ka74jnqWgO7FL40EQjA4749 J57tZOg0La/gFHTMuc0sI7UTBblGHcGG87uYtGiY/6rUzfYlm5BEX8LvUkWa5rplRxa2 /e2w== X-Forwarded-Encrypted: i=1; AJvYcCWfm/NWKTENtwtokM3uqZg9DwOUwYTtAL35fBoVyWic2BORb/7vaoaBm1ZvCsCvQyktmQY5rt+VVz4W@nongnu.org X-Gm-Message-State: AOJu0YyfO7pcNP2kjnyk3dfF+A4ecgrt7lzenqD8Rwwa4TpthDK7aByn x775yK2HhYmiqM67MANKcoBKq2JigWJ3DpaXU7DuAgNN/85unttBUESROiNoEI8= X-Gm-Gg: ASbGncvE3H9j25/c6UCuV5sR08nF8viIR1fY30zbk26ZTej6h1FTHdfDl9DQZcodd/n LTDok9TaZ8bG1STq9OH/h39kk2Gg/N+95GHNfFc3TuzvVk1uQe+YMOOjfX8zFGTCi44U9Vj3HnQ bIa3HFE5Kw2CT7M6czPhFEbLGUyTzfSxmIx+wMn9PG/TxegnfidsfboocYZMpJDwlm3pcjUIXps Jq/4qXL8fLWMHQFh6qUgnRc2UpD0O4Adu217vRUBMQhErLKnj3LXZSVpsh096WfbtQ= X-Google-Smtp-Source: AGHT+IF5f9v8LKLbJ69XF5/9FR/sat8j2yettNvtdFpwj1uYH5i5lhEhxXYdIEA76jxkRQBSubhonw== X-Received: by 2002:a05:6871:e7cd:b0:29d:f773:6f24 with SMTP id 586e51a60fabf-29df7739d04mr1614261fac.13.1732817587996; Thu, 28 Nov 2024 10:13:07 -0800 (PST) Received: from [172.20.3.167] ([187.217.227.247]) by smtp.gmail.com with ESMTPSA id 46e09a7af769-71d7c820850sm37578a34.73.2024.11.28.10.13.07 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 28 Nov 2024 10:13:07 -0800 (PST) Message-ID: Date: Thu, 28 Nov 2024 12:13:05 -0600 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH] softfloat: Allow runtime choice of default NaN value To: Peter Maydell , qemu-devel@nongnu.org References: <20241128145455.3742294-1-peter.maydell@linaro.org> Content-Language: en-US From: Richard Henderson In-Reply-To: <20241128145455.3742294-1-peter.maydell@linaro.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=2607:f8b0:4864:20::c34; envelope-from=richard.henderson@linaro.org; helo=mail-oo1-xc34.google.com X-Spam_score_int: 12 X-Spam_score: 1.2 X-Spam_bar: + X-Spam_report: (1.2 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_SBL_CSS=3.335, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=no autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On 11/28/24 08:54, Peter Maydell wrote: > Currently we hardcode the default NaN value in parts64_default_nan() > using a compile-time ifdef ladder. This is awkward for two cases: > * for single-QEMU-binary we can't hard-code target-specifics like this > * for Arm FEAT_AFP the default NaN value depends on FPCR.AH > (specifically the sign bit is different) > > Add a field to float_status to specify the default NaN value; fall > back to the old ifdef behaviour if these are not set. > > The default NaN value is specified by setting a uint8_t to a > pattern corresponding to the sign and upper fraction parts of > the NaN; the lower bits of the fraction are set from bit 0 of > the pattern. > > This is an RFC to ask for opinions on whether this is the right > way to let the target set its default NaN. I can't decide whether > I think encoding it into a uint8_t like that is clever, or merely > too clever :-) I think that's perfectly fine. > #elif defined(TARGET_HEXAGON) > - sign = 1; > - frac = ~0ULL; > + /* > + * Sign bit set, all frac bits set. This is an odd special case, > + * where our value doesn't match up with the snan_bit_is_one setting. > + * This is because for Hexagon the returned value is always -1, > + * not a real NaN value. > + */ > + dnan_pattern = 0b11111111; It's a real (signalling) nan value -- the oddity is that the default nan is not quiet. Reviewed-by: Richard Henderson r~