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From: "WolfgaNg.Hospital at arcor dot de" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug target/114835] New: AVR popcountqi2 is not fast&small as can be Date: Wed, 24 Apr 2024 15:20:42 +0000 [thread overview] Message-ID: <bug-114835-4@http.gcc.gnu.org/bugzilla/> (raw) https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114835 Bug ID: 114835 Summary: AVR popcountqi2 is not fast&small as can be Product: gcc Version: 13.2.1 Status: UNCONFIRMED Severity: normal Priority: P3 Component: target Assignee: unassigned at gcc dot gnu.org Reporter: WolfgaNg.Hospital at arcor dot de Target Milestone: --- Created attachment 58025 --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=58025&action=edit AVR assembly code for __popcountqi2 For 8-bit AVRs, the current 16-instruction __popcountqi2 uses 6 ADC instructions to establish the number of bits set in a byte. In "Bit Twiddling Hacks", Sean E. Anderson presents several approaches to this; "parallel/sideways addition" can be coded with one instruction&cycle less. When establishing the "popcount" of an uint8_t, I've seen GCC to widen the value to "half int" and use __popcountqi2 twice.
next reply other threads:[~2024-04-24 15:20 UTC|newest] Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top 2024-04-24 15:20 WolfgaNg.Hospital at arcor dot de [this message] 2024-05-07 14:32 ` [Bug target/114835] " cvs-commit at gcc dot gnu.org 2024-05-07 15:12 ` gjl at gcc dot gnu.org 2024-05-07 15:14 ` gjl at gcc dot gnu.org
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