ARM: Add a findLsbSet function and use it to implement clz.

[gem5.git] / src / base / bitfield.hh

diff --git a/src/base/bitfield.hh b/src/base/bitfield.hh
index 664093fa27fc96145ce16448afadf3264c7c3eee..cc3695159e639dc030c055ff82aa9d3a245dbf6a 100644 (file)
--- a/src/base/bitfield.hh
+++ b/src/base/bitfield.hh
@@ -32,7 +32,7 @@
 #ifndef __BASE_BITFIELD_HH__
 #define __BASE_BITFIELD_HH__
 
-#include <inttypes.h>
+#include "base/types.hh"
 
 /**
  * Generate a 64-bit mask of 'nbits' 1s, right justified.
@@ -161,4 +161,21 @@ findMsbSet(uint64_t val) {
     return msb;
 }
 
+/**
+ * Returns the bit position of the LSB that is set in the input
+ */
+inline int
+findLsbSet(uint64_t val) {
+    int lsb = 0;
+    if (!val)
+        return sizeof(val) * 8;
+    if (!bits(val, 31,0)) { lsb += 32; val >>= 32; }
+    if (!bits(val, 15,0)) { lsb += 16; val >>= 16; }
+    if (!bits(val, 7,0))  { lsb += 8;  val >>= 8;  }
+    if (!bits(val, 3,0))  { lsb += 4;  val >>= 4;  }
+    if (!bits(val, 1,0))  { lsb += 2;  val >>= 2;  }
+    if (!bits(val, 0,0))  { lsb += 1; }
+    return lsb;
+}
+
 #endif // __BASE_BITFIELD_HH__