linux-kernel - [PATCH 1/5] ARM: findbit: document ARMv5 bit offset calculation

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Message-Id: <E1ooSWP-000FDy-5t@rmk-PC.armlinux.org.uk>
Date:   Fri, 28 Oct 2022 17:47:53 +0100
From:   "Russell King (Oracle)" <rmk+kernel@...linux.org.uk>
To:     Yury Norov <yury.norov@...il.com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Mark Rutland <mark.rutland@....com>,
        Will Deacon <will@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-arm-kernel@...ts.infradead.org
Subject: [PATCH 1/5] ARM: findbit: document ARMv5 bit offset calculation

Document the ARMv5 bit offset calculation code.

Signed-off-by: Russell King (Oracle) <rmk+kernel@...linux.org.uk>
---
 arch/arm/lib/findbit.S | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/arm/lib/findbit.S b/arch/arm/lib/findbit.S
index 7fd3600db8ef..4c584bc4704b 100644
--- a/arch/arm/lib/findbit.S
+++ b/arch/arm/lib/findbit.S
@@ -172,10 +172,10 @@ ENDPROC(_find_next_bit_be)
 .L_found:
 #if __LINUX_ARM_ARCH__ >= 5
 		rsb	r0, r3, #0
-		and	r3, r3, r0
-		clz	r3, r3
-		rsb	r3, r3, #31
-		add	r0, r2, r3
+		and	r3, r3, r0		@ mask out lowest bit set
+		clz	r3, r3			@ count high zero bits
+		rsb	r3, r3, #31		@ offset of first set bit
+		add	r0, r2, r3		@ add offset of first set bit
 #else
 		tst	r3, #0x0f
 		addeq	r2, r2, #4
-- 
2.30.2