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From: "rsaxvc at gmail dot com" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug target/106484] Failure to optimize uint64_t/constant division on ARM32 Date: Sat, 08 Jul 2023 18:10:12 +0000 [thread overview] Message-ID: <bug-106484-4-7Z0kmMfk2Y@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-106484-4@http.gcc.gnu.org/bugzilla/> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106484 --- Comment #5 from rsaxvc at gmail dot com --- Related ticket requested with Clang: https://github.com/llvm/llvm-project/issues/63731 latest umulh() function is a little shorter: static uint64_t umulh(uint64_t a, uint64_t b) { const uint32_t a_lo = a; const uint32_t a_hi = a >> 32; const uint32_t b_lo = b; const uint32_t b_hi = b >> 32; /* FOIL method of multiplication See https://en.wikipedia.org/wiki/FOIL_method, but instead of binomials with constants a,b,c,d variables x,y: (ax+b) * (cy + d), consider it with variables a,b,c,d, constants x,y = 1<<32 Results in one UMULL or UMLAL(when merged with accumulate below) per multiply*/ const uint64_t acc0 = (uint64_t)a_lo * b_lo; const uint64_t acc1 = (uint64_t)a_hi * b_lo; const uint64_t acc2 = (uint64_t)a_lo * b_hi; const uint64_t acc3 = (uint64_t)a_hi * b_hi; /* Accumulate the results, keeping only the top 64-bits of the 128-bit result*/ uint64_t acc = acc0; acc >>= 32; acc += acc1; acc += acc2; acc >>= 32; acc += acc3; return acc; }
prev parent reply other threads:[~2023-07-08 18:10 UTC|newest] Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top 2022-07-30 18:38 [Bug target/106484] New: " rsaxvc at gmail dot com 2022-07-30 18:39 ` [Bug target/106484] " rsaxvc at gmail dot com 2022-07-30 22:29 ` pinskia at gcc dot gnu.org 2022-08-01 10:50 ` rearnsha at gcc dot gnu.org 2022-08-01 12:12 ` rsaxvc at gmail dot com 2023-05-04 12:55 ` rsaxvc at gmail dot com 2023-07-08 18:10 ` rsaxvc at gmail dot com [this message]
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