MdePkg/BaseSynchronizationLib: Add InterlockedCompareExchange16

This implements the function InterlockedCompareExchange16 () for all
architectures, using architecture and toolchain specific intrinsics
or primitive assembler instructions.

Contributed-under: TianoCore Contribution Agreement 1.0
Reviewed-by: Olivier Martin <olivier.martin@arm.com>
Acked-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Michael Kinney <michael.d.kinney@intel.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Laszlo Ersek <lersek@redhat.com>

git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@16966 6f19259b-4bc3-4df7-8a09-765794883524

MdePkg/Library/BaseSynchronizationLib/X64/GccInline.c

@@ -88,6 +88,50 @@ InternalSyncDecrement (
 }
 
 
+/**
+  Performs an atomic compare exchange operation on a 16-bit unsigned integer.
+
+  Performs an atomic compare exchange operation on the 16-bit unsigned integer
+  specified by Value.  If Value is equal to CompareValue, then Value is set to
+  ExchangeValue and CompareValue is returned.  If Value is not equal to CompareValue,
+  then Value is returned.  The compare exchange operation must be performed using
+  MP safe mechanisms.
+
+
+  @param  Value         A pointer to the 16-bit value for the compare exchange
+                        operation.
+  @param  CompareValue  16-bit value used in compare operation.
+  @param  ExchangeValue 16-bit value used in exchange operation.
+
+  @return The original *Value before exchange.
+
+**/
+UINT16
+EFIAPI
+InternalSyncCompareExchange16 (
+  IN OUT volatile  UINT16           *Value,
+  IN      UINT16                    CompareValue,
+  IN      UINT16                    ExchangeValue
+  )
+{
+
+
+  __asm__ __volatile__ (
+    "lock                 \n\t"
+    "cmpxchgw    %3, %1       "
+    : "=a" (CompareValue),
+      "=m" (*Value)
+    : "a"  (CompareValue),
+      "r"  (ExchangeValue),
+      "m"  (*Value)
+    : "memory",
+      "cc"
+    );
+
+  return CompareValue;
+}
+
+
 /**
   Performs an atomic compare exchange operation on a 32-bit unsigned integer.