issue-442: Fixes an issue encountered on PPC with undefined conversions from 'base::subtle::Atomic64*' to 'const volatile Atomic32*'

git-svn-id: http://gperftools.googlecode.com/svn/trunk@160 6b5cf1ce-ec42-a296-1ba9-69fdba395a50

1 files changed, 19 insertions, 0 deletions

diff --git a/src/base/spinlock_internal.cc b/src/base/spinlock_internal.cc
index b9fadde..172a637 100644
--- a/src/base/spinlock_internal.cc
+++ b/src/base/spinlock_internal.cc
@@ -80,6 +80,7 @@ int32 SpinLockWait(volatile Atomic32 *w, int n,
 static int SuggestedDelayNS(int loop) {
   // Weak pseudo-random number generator to get some spread between threads
   // when many are spinning.
+#ifdef BASE_HAS_ATOMIC64
   static base::subtle::Atomic64 rand;
   uint64 r = base::subtle::NoBarrier_Load(&rand);
   r = 0x5deece66dLL * r + 0xb;   // numbers from nrand48()
@@ -96,6 +97,24 @@ static int SuggestedDelayNS(int loop) {
   // The futex path multiplies this by 16, since we expect explicit wakeups
   // almost always on that path.
   return r >> (44 - (loop >> 3));
+#else
+  static Atomic32 rand;
+  uint32 r = base::subtle::NoBarrier_Load(&rand);
+  r = 0x343fd * r + 0x269ec3;   // numbers from MSVC++
+  base::subtle::NoBarrier_Store(&rand, r);
+
+  r <<= 1;   // 31-bit random number now in top 31-bits.
+  if (loop < 0 || loop > 32) {   // limit loop to 0..32
+    loop = 32;
+  }
+  // loop>>3 cannot exceed 4 because loop cannot exceed 32.
+  // Select top 20..24 bits of lower 31 bits,
+  // giving approximately 0ms to 16ms.
+  // Mean is exponential in loop for first 32 iterations, then 8ms.
+  // The futex path multiplies this by 16, since we expect explicit wakeups
+  // almost always on that path.
+  return r >> (12 - (loop >> 3));
+#endif
 }
 
 } // namespace internal