fix(sampling): preserve deterministic sampler rate

Author: MilanGarnier

dd-trace-core/src/main/java/datadog/trace/common/sampling/DeterministicSampler.java

@@ -38,11 +38,11 @@ protected <T extends CoreSpan<T>> long getSamplingId(T span) {
 
   private static final double MAX = Math.pow(2, 64) - 1;
 
-  private final float rate;
+  private final double rate;
   private final long threshold;
 
   public DeterministicSampler(final double rate) {
-    this.rate = (float) rate;
+    this.rate = rate;
     this.threshold = cutoff(rate);
   }
 

dd-trace-core/src/test/java/datadog/trace/common/sampling/DeterministicTraceSamplerTest.java

@@ -357,6 +357,15 @@ void testSamplingAll(String traceId) {
     assertTrue(sampler.sample(span));
   }
 
+  @TableTest({
+    "rate       ",
+    "0.123456789",
+    "0.999999999"
+  })
+  void preservesConfiguredSampleRate(double rate) {
+    assertEquals(rate, new DeterministicSampler.TraceSampler(rate).getSampleRate());
+  }
+
   @ParameterizedTest(name = "rate={0}")
   @MethodSource("testCutoffCalculationArguments")
   void testCutoffCalculation(int rate) {