Date: Wed, 10 Jun 2026 18:53:11 -0700 From: Adrian Chadd <adrian@freebsd.org> To: Piotr Kubaj <pkubaj@freebsd.org> Cc: freebsd-ppc@freebsd.org Subject: Re: Proposal to switch powerpc64le to IEEE-754 binary128 Message-ID: <CAJ-VmonbXXpq4TBZ38idRPVHM1h%2BSFChvyr3DhVjHkVeaw9KjA@mail.gmail.com> In-Reply-To: <ah8sFn_mmGrJp9Ru@talos-powerpc64le>
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So, a few of us chatted in IRC about it. * The minimum for PPC64LE was POWER7 anyway, right? * There's no easy way to deal with this in library versioning and such, so we should just rip the bandaid off * We can fix the ports as they come up. * people wishing to run stuff built on -15 or earlier should just run a userland jail. so given that! * Please include something to propose to put in UPDATING * Please explain what will happen with all the toolchains in -HEAD (eg all the gcc versions will use the right base type, we won't have gcc compiling a different ABI to llvm21, etc) * Let's figure out when the flag day should be. -adrian On Tue, 2 Jun 2026 at 13:04, Piotr Kubaj <pkubaj@freebsd.org> wrote: > > Hello, > > as you may know, FreeBSD currently uses 64-bit long double. Since plain > double is also 64-bit, long double actually gives no advantage over > double and is actually the same type. > > However, we can do better, at least on powerpc64le. On Linux with glibc, > many distros have already switched to IEEE-754 binary128, which is > 128-bit long double. On FreeBSD, aarch64 and riscv64 already use 128-bit > long double. > Apart from the arguments "others do it", 128-bit long double provides > obviously better precision - it's analogous to float vs double. > Operations on long doubles are also slower and variables take twice as > much memory, but that's expected of bigger types. > > Upgrades are another issue: LLVM uses different functions for operations > on 64-bit long doubles and on binary128. This means that after upgrades, > software using long doubles will need to be rebuilt. Otherwise, there's > a risk of strange issues. I have verified that bootstraps for all the > major languages work fine (rust, ghc, sbcl, openjdk), but I assume that > some scientific software may have issues. > > The current patchset is at: https://reviews.freebsd.org/D57388 > > Some ports will probably also need to be patched, but that's another > issue. > > If you have some spare system for testing, I recommend a try and a > report, straight "make buildworld installworld" is expected to work. > > I have a powerpc64le VM where it works: > root@ieeeldbl:~ # echo | cc -dM -E - | grep LDBL > #define __DECIMAL_DIG__ __LDBL_DECIMAL_DIG__ > #define __LDBL_DECIMAL_DIG__ 36 > #define __LDBL_DENORM_MIN__ 6.47517511943802511092443895822764655e-4966L > #define __LDBL_DIG__ 33 > #define __LDBL_EPSILON__ 1.92592994438723585305597794258492732e-34L > #define __LDBL_HAS_DENORM__ 1 > #define __LDBL_HAS_INFINITY__ 1 > #define __LDBL_HAS_QUIET_NAN__ 1 > #define __LDBL_MANT_DIG__ 113 > #define __LDBL_MAX_10_EXP__ 4932 > #define __LDBL_MAX_EXP__ 16384 > #define __LDBL_MAX__ 1.18973149535723176508575932662800702e+4932L > #define __LDBL_MIN_10_EXP__ (-4931) > #define __LDBL_MIN_EXP__ (-16381) > #define __LDBL_MIN__ 3.36210314311209350626267781732175260e-4932L > #define __LDBL_NORM_MAX__ 1.18973149535723176508575932662800702e+4932L > > On a system with the current default, 64-bit long double, the following > will be reported: > root@blackbird:~ # echo | cc -dM -E - | grep LDBL > #define __DECIMAL_DIG__ __LDBL_DECIMAL_DIG__ > #define __LDBL_DECIMAL_DIG__ 17 > #define __LDBL_DENORM_MIN__ 4.9406564584124654e-324L > #define __LDBL_DIG__ 15 > #define __LDBL_EPSILON__ 2.2204460492503131e-16L > #define __LDBL_HAS_DENORM__ 1 > #define __LDBL_HAS_INFINITY__ 1 > #define __LDBL_HAS_QUIET_NAN__ 1 > #define __LDBL_MANT_DIG__ 53 > #define __LDBL_MAX_10_EXP__ 308 > #define __LDBL_MAX_EXP__ 1024 > #define __LDBL_MAX__ 1.7976931348623157e+308L > #define __LDBL_MIN_10_EXP__ (-307) > #define __LDBL_MIN_EXP__ (-1021) > #define __LDBL_MIN__ 2.2250738585072014e-308L > #define __LDBL_NORM_MAX__ 1.7976931348623157e+308Lhome | help
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