[win-pv-devel] [PATCH 03/10] Use InterlockedBitTestAnd[Set|Reset] in SHARED_INFO

[Paul Durrant <paul.durrant@xxxxxxxxxx>]

Rather then using InterlockedCompareAndExchange to set and clear bits
in the SHARED_INFO event channel masks, use
InterlockedBitTestAnd[Set|Reset] as these will resolve to instrinsics
when available.

Signed-off-by: Paul Durrant <paul.durrant@xxxxxxxxxx>
---
 src/xenbus/shared_info.c | 26 ++++----------------------
 1 file changed, 4 insertions(+), 22 deletions(-)

diff --git a/src/xenbus/shared_info.c b/src/xenbus/shared_info.c
index 9a6af3a..41c99cf 100644
--- a/src/xenbus/shared_info.c
+++ b/src/xenbus/shared_info.c
@@ -74,21 +74,12 @@ SharedInfoSetBit(
     IN  ULONG               Bit
     )
 {
-    ULONG_PTR               Old;
-    ULONG_PTR               New;
-
     ASSERT3U(Bit, <, sizeof (ULONG_PTR) * 8);
 
     KeMemoryBarrier();
 
-    do {
-        Old = *Mask;
-        New = Old | ((ULONG_PTR)1 << Bit);
-    } while (InterlockedCompareExchangePointer((PVOID *)Mask, (PVOID)New, 
(PVOID)Old) != (PVOID)Old);
-
-    KeMemoryBarrier();
-
-    return (Old & ((ULONG_PTR)1 << Bit)) ? FALSE : TRUE;    // return TRUE if 
we set the bit
+    // return TRUE if we set the bit
+    return (InterlockedBitTestAndSet((LONG *)Mask, Bit) == 0) ? TRUE : FALSE;
 }
 
 static BOOLEAN
@@ -97,21 +88,12 @@ SharedInfoClearBit(
     IN  ULONG               Bit
     )
 {
-    ULONG_PTR               Old;
-    ULONG_PTR               New;
-
     ASSERT3U(Bit, <, sizeof (ULONG_PTR) * 8);
 
     KeMemoryBarrier();
 
-    do {
-        Old = *Mask;
-        New = Old & ~((ULONG_PTR)1 << Bit);
-    } while (InterlockedCompareExchangePointer((PVOID *)Mask, (PVOID)New, 
(PVOID)Old) != (PVOID)Old);
-
-    KeMemoryBarrier();
-
-    return (Old & ((ULONG_PTR)1 << Bit)) ? TRUE : FALSE;    // return TRUE if 
we cleared the bit
+    // return TRUE if we cleared the bit
+    return (InterlockedBitTestAndReset((LONG *)Mask, Bit) != 0) ? TRUE : FALSE;
 }
 
 static BOOLEAN
-- 
2.1.1


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