From mboxrd@z Thu Jan 1 00:00:00 1970 X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on inbox.vuxu.org X-Spam-Level: X-Spam-Status: No, score=-2.0 required=5.0 tests=MAILING_LIST_MULTI, RCVD_IN_DNSWL_MED,RCVD_IN_MSPIKE_H3,RCVD_IN_MSPIKE_WL,RDNS_NONE, SPF_PASS autolearn=ham autolearn_force=no version=3.4.2 Received: (qmail 19426 invoked from network); 22 Mar 2020 01:20:14 -0000 Received-SPF: pass (mother.openwall.net: domain of lists.openwall.com designates 195.42.179.200 as permitted sender) receiver=inbox.vuxu.org; client-ip=195.42.179.200 envelope-from= Received: from unknown (HELO mother.openwall.net) (195.42.179.200) by inbox.vuxu.org with ESMTP; 22 Mar 2020 01:20:14 -0000 Received: (qmail 3663 invoked by uid 550); 22 Mar 2020 01:20:11 -0000 Mailing-List: contact musl-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Reply-To: musl@lists.openwall.com Received: (qmail 3642 invoked from network); 22 Mar 2020 01:20:10 -0000 Date: Sat, 21 Mar 2020 21:19:58 -0400 From: Rich Felker To: musl@lists.openwall.com Message-ID: <20200322011958.GM11469@brightrain.aerifal.cx> References: <20200114185058.GV23985@port70.net> <20200114185835.GG30412@brightrain.aerifal.cx> <20200206145156.GF1663@brightrain.aerifal.cx> <20200222195925.GK1663@brightrain.aerifal.cx> <20200223001942.GM1663@brightrain.aerifal.cx> <20200320181250.GC11469@brightrain.aerifal.cx> MIME-Version: 1.0 Content-Type: multipart/mixed; boundary="69pVuxX8awAiJ7fD" Content-Disposition: inline In-Reply-To: <20200320181250.GC11469@brightrain.aerifal.cx> User-Agent: Mutt/1.5.21 (2010-09-15) Subject: Re: [musl] Q: dealing with missing removal of excess precision --69pVuxX8awAiJ7fD Content-Type: text/plain; charset=us-ascii Content-Disposition: inline On Fri, Mar 20, 2020 at 02:12:50PM -0400, Rich Felker wrote: > On Sun, Feb 23, 2020 at 07:14:08PM +0300, Alexander Monakov wrote: > > On Sat, 22 Feb 2020, Rich Felker wrote: > > > > > I'm not well acquainted with SSE, and only so-so with x87, so pretty > > > much I'm reading them for higher-level issues with tooling > > > compatibility (like the concerns I already raised and looked up and > > > seem to have resolved about x87 constraints and non-GCC compilers) and > > > logic, then planning to apply and test them. I think being aware of > > > non-obvious mistake modes that have already been found would be a lot > > > more useful than staring at things, especially if the bugs you've > > > found are in subtleties of the insn behavior or constraint behavior. > > > > Okay, thanks. I found two issues: > > > > 1. i386 lrint* functions mistakenly used fistpll instead of fistpl (I > > posted the fix for x32 asm after noticing my own mistake). > > > > 2. Some functions bind a 32-bit lvalue as output for fnstsw %ax, which > > as the operand says writes only 16 bits. They should be changed to either > > use a 16-bit lvalue, or a zero-initialized 32-bit lvalue with "+a" constraint. > > > > Plus, not bugs, but still worth mentioning: > > > > 3. The new remquol in C could alternatively be implemented by using fxam > > to extract sign bits instead of loading them from stack slots. The current > > approach makes sense given the ABI, but an implementation aiming for better > > code after inlining could choose to use fxam instead of forcing a spill. > > > > 4. I did not manage to find a copy of Figueroa's "When is double rounding > > innocuous", but I could cite e.g. "Innocuous Double Rounding of Basic > > Arithmetic Operations" by Pierre Roux instead (in i386/sqrtf.c). > > > > If you like you can fetch a Git tree with my patches from > > > > https://git.sr.ht/~amonakov/musl > > > > (issue 1 is already corrected in that repo) > > Hi. I'm trying to catch up on this and other patches after being sick > and not getting much done for a while. Is there anything else I should > be aware of before going forward with these? > > One minor cosmetic change I'd like to make to commit names if you > don't object is changing "x86-family" to "x87-family" for the commits > that are "i386 + long double functions on x86_64" since I found it > confusing when there's one commit for "x86 family" then a separate one > for x86_64 versions of the same function. Let me know if you think of > any alternative that might be more clear than "x87" With the fixups mentioned (included in attached patches), i386 and x86_64 are passing libc-test and seem fine. OK if I merge them (rebasing the fixups in as fixups)? With s/x86/x87/ naming? Rich --69pVuxX8awAiJ7fD Content-Type: text/plain; charset=us-ascii Content-Disposition: attachment; filename="0001-fabsf-i386-fixup.patch" >From 3f99f4595aa3ce528008ee22d65512768376a9a6 Mon Sep 17 00:00:00 2001 From: Rich Felker Date: Sat, 21 Mar 2020 16:23:51 -0400 Subject: [PATCH 1/3] fabsf i386 fixup --- src/math/i386/fabsf.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/src/math/i386/fabsf.c b/src/math/i386/fabsf.c index d07be321..d882eee3 100644 --- a/src/math/i386/fabsf.c +++ b/src/math/i386/fabsf.c @@ -1,6 +1,6 @@ #include -float fabs(float x) +float fabsf(float x) { __asm__ ("fabs" : "+t"(x)); return x; -- 2.21.0 --69pVuxX8awAiJ7fD Content-Type: text/plain; charset=us-ascii Content-Disposition: attachment; filename="0002-sqrt-i386-fixup.patch" >From 7fd1bc3b8ecf61d758498edd7f4a75a079ee8df5 Mon Sep 17 00:00:00 2001 From: Rich Felker Date: Sat, 21 Mar 2020 16:24:04 -0400 Subject: [PATCH 2/3] sqrt i386 fixup --- src/math/i386/sqrt.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/src/math/i386/sqrt.c b/src/math/i386/sqrt.c index 619df056..934fbcca 100644 --- a/src/math/i386/sqrt.c +++ b/src/math/i386/sqrt.c @@ -10,6 +10,6 @@ double sqrt(double x) /* Rounding to double would have encountered an exact halfway case. Adjust mantissa downwards if fsqrt rounded up, else upwards. (result of fsqrt could not have been exact) */ - ux.i.m ^= (fpsr & 0x200) + 0x200; + ux.i.m ^= (fpsr & 0x200) + 0x300; return (double)ux.f; } -- 2.21.0 --69pVuxX8awAiJ7fD Content-Type: text/plain; charset=us-ascii Content-Disposition: attachment; filename="0003-sqrt-i386-fixup-2.patch" >From b60ddebd251ff28559b48aa758026da8fbbab3f7 Mon Sep 17 00:00:00 2001 From: Rich Felker Date: Sat, 21 Mar 2020 16:57:38 -0400 Subject: [PATCH 3/3] sqrt i386 fixup 2 --- src/math/i386/sqrt.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/src/math/i386/sqrt.c b/src/math/i386/sqrt.c index 934fbcca..a34f4ce8 100644 --- a/src/math/i386/sqrt.c +++ b/src/math/i386/sqrt.c @@ -3,7 +3,7 @@ double sqrt(double x) { union ldshape ux; - unsigned fpsr; + unsigned short fpsr; __asm__ ("fsqrt; fnstsw %%ax": "=t"(ux.f), "=a"(fpsr) : "0"(x)); if ((ux.i.m & 0x7ff) != 0x400) return (double)ux.f; -- 2.21.0 --69pVuxX8awAiJ7fD--