= core: introduce fastMod operation in Sampler

2 files changed, 16 insertions, 2 deletions

diff --git a/kamon-core/src/main/resources/reference.conf b/kamon-core/src/main/resources/reference.conf
index 7c4b4ecb..d7276b53 100644
--- a/kamon-core/src/main/resources/reference.conf
+++ b/kamon-core/src/main/resources/reference.conf
@@ -147,7 +147,8 @@ kamon {
     # Use a AtomicLong to ensure that every .sample-interval number of requests tracing information will be gathered and
     # reported.
     ordered-sampler {
-      sample-interval = 10
+      # must be power of two
+      sample-interval = 8
     }
 
     # Gather tracing information for all traces but only report those whose elapsed-time is equal or greated to the
diff --git a/kamon-core/src/main/scala/kamon/trace/Sampler.scala b/kamon-core/src/main/scala/kamon/trace/Sampler.scala
index be6ace69..9c6e5e63 100644
--- a/kamon-core/src/main/scala/kamon/trace/Sampler.scala
+++ b/kamon-core/src/main/scala/kamon/trace/Sampler.scala
@@ -44,14 +44,27 @@ class RandomSampler(chance: Int) extends Sampler {
 }
 
 class OrderedSampler(interval: Int) extends Sampler {
+  import OrderedSampler._
+
   require(interval > 0, "kamon.trace.ordered-sampler.interval cannot be <= 0")
+  assume(interval isPowerOfTwo, "kamon.trace.ordered-sampler.interval must be power of two")
 
   private val sequencer = Sequencer()
 
-  def shouldTrace: Boolean = sequencer.next() % interval == 0
+  def shouldTrace: Boolean = (sequencer.next() fastMod interval) == 0
   def shouldReport(traceElapsedTime: NanoInterval): Boolean = true
 }
 
+object OrderedSampler {
+  implicit class EnhancedInt(i: Int) {
+    def isPowerOfTwo = !((i & (i - 1)) == 0)
+  }
+
+  implicit class EnhancedLong(dividend: Long) {
+    def fastMod(divisor: Int) = dividend & (divisor - 1)
+  }
+}
+
 class ThresholdSampler(thresholdInNanoseconds: Long) extends Sampler {
   require(thresholdInNanoseconds > 0, "kamon.trace.threshold-sampler.minimum-elapsed-time cannot be <= 0")