[xen staging] x86/bitops: adjust partial first word handling in __find_next{,_zero}_bit()

[patchbot@xxxxxxx]

commit 0e6f9fbb8a7724e6cb73733a68a60b64f841ea61
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Mon Feb 23 08:43:29 2026 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Mon Feb 23 08:43:29 2026 +0100

    x86/bitops: adjust partial first word handling in __find_next{,_zero}_bit()
    
    There's no need to subtract "bit" in what is passed to __scanbit(), as the
    other bits are zero anyway after the shift (in __find_next_bit()) or can
    be made so (in __find_next_zero_bit()) by flipping negation and shift. (We
    actually leverage the same facts in find_next{,_zero}_bit() as well.) This
    way in __scanbit() the TZCNT alternative can be engaged.
    
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Acked-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
 xen/arch/x86/bitops.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/xen/arch/x86/bitops.c b/xen/arch/x86/bitops.c
index 720ab32362..22cfb6d8ec 100644
--- a/xen/arch/x86/bitops.c
+++ b/xen/arch/x86/bitops.c
@@ -35,8 +35,8 @@ unsigned int __find_next_bit(
     if ( bit != 0 )
     {
         /* Look for a bit in the first word. */
-        set = __scanbit(*p >> bit, BITS_PER_LONG - bit);
-        if ( set < (BITS_PER_LONG - bit) )
+        set = __scanbit(*p >> bit, BITS_PER_LONG);
+        if ( set < BITS_PER_LONG )
             return (offset + set);
         offset += BITS_PER_LONG - bit;
         p++;
@@ -85,8 +85,8 @@ unsigned int __find_next_zero_bit(
     if ( bit != 0 )
     {
         /* Look for zero in the first word. */
-        set = __scanbit(~(*p >> bit), BITS_PER_LONG - bit);
-        if ( set < (BITS_PER_LONG - bit) )
+        set = __scanbit(~*p >> bit, BITS_PER_LONG);
+        if ( set < BITS_PER_LONG )
             return (offset + set);
         offset += BITS_PER_LONG - bit;
         p++;
--
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