From patchwork Fri Apr 5 23:38:04 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Zack Buhman X-Patchwork-Id: 13619578 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 DD6DDC3A59D for ; Fri, 5 Apr 2024 23:39:46 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1rst98-0000O0-TI; Fri, 05 Apr 2024 19:38:59 -0400 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 1rst97-0000Nm-QA for qemu-devel@nongnu.org; Fri, 05 Apr 2024 19:38:57 -0400 Received: from fout5-smtp.messagingengine.com ([103.168.172.148]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1rst95-00056A-KS for qemu-devel@nongnu.org; Fri, 05 Apr 2024 19:38:57 -0400 Received: from compute7.internal (compute7.nyi.internal [10.202.2.48]) by mailfout.nyi.internal (Postfix) with ESMTP id 21FBE1380522; Fri, 5 Apr 2024 19:38:54 -0400 (EDT) Received: from mailfrontend2 ([10.202.2.163]) by compute7.internal (MEProxy); Fri, 05 Apr 2024 19:38:54 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=buhman.org; h=cc :cc:content-transfer-encoding:content-type:date:date:from:from :in-reply-to:in-reply-to:message-id:mime-version:references :reply-to:subject:subject:to:to; s=fm2; t=1712360334; x= 1712446734; bh=JyJaA02OJsx/nB58pukq3CZO30p1iPwHkLUv67ne780=; b=V lweo7W3mxweyjbRE82hCo+jbvzVjnPtcasmKd7305UNAKWLt/lfcunExT0Rgiith N7UbrfeX1xmfnD+GTVfVNKXr5jn8/3AX6vezpdpIs/2yN3RDn/BeHFn4Fd2oWbyl HFd4MMNOLWS48oiU6AqJm6Cd8Mt+xGzHejefxuAXpmar3wzrFCx4w+Cc8VQLCpkQ /+g4S4ALhJAw5tef/ssUjg1ufHjFuX514T02TEw4U4pNEoTfqfd5XJvzrKYNxg9p Z5CDAY+iC0G5iKvrTXjc5TGMhfHeMpRsGyHhaF6vFTEKTf3pMOevpIDy7bUhp5F7 gPoLnTt8duQDz+hPa+0Gw== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d= messagingengine.com; h=cc:cc:content-transfer-encoding :content-type:date:date:feedback-id:feedback-id:from:from :in-reply-to:in-reply-to:message-id:mime-version:references :reply-to:subject:subject:to:to:x-me-proxy:x-me-proxy :x-me-sender:x-me-sender:x-sasl-enc; s=fm2; t=1712360334; x= 1712446734; bh=JyJaA02OJsx/nB58pukq3CZO30p1iPwHkLUv67ne780=; b=u otH/Z+2cP9n0JPcVjcPhbn+I8jDXinm0MpwYbEAl1zpKiS8LT/GOJgkjkPDaIlKH hUE7v/6Og0sAD1IamIDv8MPKB8BksioprzUUV9xcnpZ+nvsuxn8C5oE3fBHMjxyT iTRYmA75Z/aULN7XDcWFHsACBvpJq4fdMJPOfQNy/b3FzlPOHahDqs+9cQex/8Ag 6LMvzQE/xLvGt5qKaU3RKnnf2rfhvfnSdRRCcHfja9ArKzuMsE2yzncQq4FCGuit gVMF+NybO98WpWMPrqaKBv55rlnN4+gCnYvcTwjRZRS2aq0MfncIFfzYJAnP26f6 7cYPYHOk6MYzsHADWtSqA== X-ME-Sender: X-ME-Received: X-ME-Proxy-Cause: gggruggvucftvghtrhhoucdtuddrgedvledrudeguddgvdegucetufdoteggodetrfdotf fvucfrrhhofhhilhgvmecuhfgrshhtofgrihhlpdfqfgfvpdfurfetoffkrfgpnffqhgen uceurghilhhouhhtmecufedttdenucenucfjughrpefhvfevufffkffojghfggfgsedtke ertdertddtnecuhfhrohhmpegkrggtkhcuuehuhhhmrghnuceoiigrtghksegsuhhhmhgr nhdrohhrgheqnecuggftrfgrthhtvghrnhepvefhhedtveefvefgieehledtkeegvdefvd eftdffteehfeejhfejteeitdfgtdejnecuvehluhhsthgvrhfuihiivgeptdenucfrrghr rghmpehmrghilhhfrhhomhepiigrtghksegsuhhhmhgrnhdrohhrgh X-ME-Proxy: Feedback-ID: i1541475f:Fastmail Received: by mail.messagingengine.com (Postfix) with ESMTPA; Fri, 5 Apr 2024 19:38:50 -0400 (EDT) From: Zack Buhman To: qemu-devel@nongnu.org Cc: peter.maydell@linaro.org, ysato@users.sourceforge.jp, Zack Buhman Subject: [PATCH v2] sh4: mac.w: implement saturation arithmetic logic Date: Sat, 6 Apr 2024 07:38:04 +0800 Message-ID: <20240405233802.29128-3-zack@buhman.org> X-Mailer: git-send-email 2.41.0 In-Reply-To: References: MIME-Version: 1.0 Received-SPF: pass client-ip=103.168.172.148; envelope-from=zack@buhman.org; helo=fout5-smtp.messagingengine.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 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_LOW=-0.7, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham 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 The saturation arithmetic logic in helper_macw is not correct. I tested and verified this behavior on a SH7091, the general pattern is a code sequence such as: sets mov.l _mach,r2 lds r2,mach mov.l _macl,r2 lds r2,macl mova _n,r0 mov r0,r1 mova _m,r0 mac.w @r0+,@r1+ _mach: .long 0xffffffff _macl: .long 0xfffffffe _m: .word 0x0002 .word 0 _n: .word 0x0003 .word 0 test 0: (mach should not be modified if an overflow did not occur) given, prior to saturation mac.l: mach = 0xffffffff ; macl = 0xfffffffe @r0 = 0x0002 ; @r1 = 0x0003 expected saturation mac.w result: mach = 0xffffffff (unchanged) macl = 0x00000004 qemu saturation mac.w result (before this commit): mach = 0x00000001 macl = 0x80000000 In the context of the helper_macw implementation prior to this commit, initially this appears to be a surprising result. This is because (prior to unary negation) the C literal `0x80000000` (due to being outside the range of a `signed int`) is evaluated as an `unsigned int` whereas the literal `1` (due to being inside the range of `signed int`) is evaluated as `signed int`, as in: static_assert(1 < -0x80000000 == 1); static_assert(1 < -1 == 0); This is because the unary negation of an unsigned int is an unsigned int. In other words, if the `res < -0x80000000` comparison used infinite-precision literals, the saturation mac.w result would have been: mach = 0x00000000 macl = 0x00000004 Due to this (forgivable) misunderstanding of C literals, the following behavior also occurs: test 1: (`2 * 3 + 0` is not an overflow) given, prior to saturation mac.l: mach = 0x00000000 ; macl = 0x00000000 @r0 = 0x0002 ; @r1 = 0x0003 expected saturation mac.w result: mach = 0x00000000 (unchanged) macl = 0x00000006 qemu saturation mac.w result (before this commit): mach = 0x00000001 macl = 0x80000000 test 2: (mach should not be accumulated in saturation mode) (16-bit operands are sign-extended) given, prior to saturation mac.l: mach = 0x12345678 ; macl = 0x7ffffffe @r0 = 0x0002 ; @r1 = 0xfffd expected saturation mac.w result: mach = 0x12345678 (unchanged) macl = 0x7ffffff8 qemu saturation mac.w result (before this commit): mach = 0x00000001 macl = 0x7fffffff test 3: (macl should have the correct saturation value) given, prior to saturation mac.l: mach = 0xabcdef12 ; macl = 0x7ffffffa @r0 = 0x0002 ; @r1 = 0x0003 expected saturation mac.w result: mach = 0x00000001 (overwritten) macl = 0x7fffffff qemu saturation mac.w result (before this commit): mach = 0x00000001 macl = 0x80000000 All of the above also matches the description of MAC.W as documented in cd00147165-sh-4-32-bit-cpu-core-architecture-stmicroelectronics.pdf Signed-off-by: Zack Buhman --- target/sh4/op_helper.c | 45 ++++++++++++++++++++++++++++++++---------- 1 file changed, 35 insertions(+), 10 deletions(-) diff --git a/target/sh4/op_helper.c b/target/sh4/op_helper.c index ee16524083..07ff2cf53d 100644 --- a/target/sh4/op_helper.c +++ b/target/sh4/op_helper.c @@ -187,20 +187,45 @@ void helper_macl(CPUSH4State *env, uint32_t arg0, uint32_t arg1) void helper_macw(CPUSH4State *env, uint32_t arg0, uint32_t arg1) { - int64_t res; + int16_t value0 = (int16_t)arg0; + int16_t value1 = (int16_t)arg1; + int32_t mul = ((int32_t)value0) * ((int32_t)value1); - res = ((uint64_t) env->mach << 32) | env->macl; - res += (int64_t) (int16_t) arg0 *(int64_t) (int16_t) arg1; - env->mach = (res >> 32) & 0xffffffff; - env->macl = res & 0xffffffff; + /* Perform 32-bit saturation arithmetic if the S flag is set */ if (env->sr & (1u << SR_S)) { - if (res < -0x80000000) { - env->mach = 1; - env->macl = 0x80000000; - } else if (res > 0x000000007fffffff) { + const int32_t upper_bound = ((1u << 31) - 1); + const int32_t lower_bound = -((1u << 31) - 0); + + /* + * In saturation arithmetic mode, the accumulator is 32-bit + * with carry. MACH is not considered during the addition + * operation nor the 32-bit saturation logic. + */ + int32_t mac = env->macl; + int32_t result; + bool overflow = sadd32_overflow(mac, mul, &result); + if (overflow) { + result = (mac < 0) ? lower_bound : upper_bound; + /* MACH is set to 1 to denote overflow */ + env->macl = result; env->mach = 1; - env->macl = 0x7fffffff; + } else { + /* + * If there is no overflow, the result is already inside + * the saturation bounds. + * + * If there was no overflow, MACH is unchanged. + */ + env->macl = result; } + } else { + /* In non-saturation arithmetic mode, the accumulator is 64-bit */ + int64_t mac = (((uint64_t)env->mach) << 32) | env->macl; + + /* The carry bit of the 64-bit addition is discarded */ + int64_t result = mac + (int64_t)mul; + env->macl = result; + env->mach = result >> 32; } }