ARM: Be more smart about switching instructions when immediates...

src/utils.h

Index: src/utils.h
===================================================================
--- src/utils.h	(revision 4849)
+++ src/utils.h	(working copy)
@@ -47,6 +47,36 @@
 }
 
 
+// X must be a power of 2.  Returns the number of trailing zeros.
+template <typename T>
+static inline int WhichPowerOf2(T x) {

[Søren Thygesen Gjesse, 2010/06/14 07:56:47]

Shouldn't there be a test case for this?

[Erik Corry, 2010/06/14 21:05:46]

Assert added.

+  ASSERT(IsPowerOf2(x));
+  if (x < 0) return 31;
+  if (x == 0) return 32;
+  int bits = 0;
+  if (x >= 0x10000) {
+    bits += 16;
+    x >>= 16;
+  }
+  if (x >= 0x100) {
+    bits += 8;
+    x >>= 8;
+  }
+  if (x >= 0x10) {
+    bits += 4;
+    x >>= 4;
+  }
+  switch (x) {
+    case 1: return bits;
+    case 2: return bits + 1;
+    case 4: return bits + 2;
+    case 8: return bits + 3;
+    default: UNREACHABLE();
+  }
+  return 0;
+}
+
+
 // The C++ standard leaves the semantics of '>>' undefined for
 // negative signed operands. Most implementations do the right thing,
 // though.