Fix BigInt random_integer() distribution issue.

Fixes #108

1 files changed, 97 insertions, 0 deletions

diff --git a/src/tests/catchy/test_bigint.cpp b/src/tests/catchy/test_bigint.cpp
index 5f4c960cf..9bd99e919 100644
--- a/src/tests/catchy/test_bigint.cpp
+++ b/src/tests/catchy/test_bigint.cpp
@@ -71,4 +71,101 @@ TEST_CASE("Bigint basics", "[bigint]")
       }
    }
 
+TEST_CASE("Bigint random_integer", "[bigint]")
+   {
+   RandomNumberGenerator *rng = RandomNumberGenerator::make_rng();
+
+   SECTION("min is 0")
+      {
+      // 0–9
+      const size_t MIN = 0;
+      const size_t MAX = 10; // excluded
+      const int ITERATIONS = 10000;
+
+      std::vector<int> counts(MAX, 0);
+      std::vector<double> ratios(MAX, 1.0);
+
+      for (size_t i = 0; i < ITERATIONS; i++)
+         {
+         BigInt b = BigInt::random_integer(*rng, MIN, MAX);
+         size_t x = b.to_u32bit();
+         counts[x]++;
+         }
+
+      std::stringstream debug;
+      for (size_t d = MIN; d < MAX; ++d)
+         {
+         auto ratio = static_cast<double>(counts[d]) / ITERATIONS;
+         ratios[d] = ratio;
+
+         if (!debug.str().empty())
+            {
+            debug << ", ";
+            }
+         debug << d << ": " << std::setprecision(3) << ratio;
+         }
+
+      INFO( debug.str() )
+
+      // Have ~ 10 % on each digit from 0-9
+      CHECK(( 0.09 < ratios[0] )); CHECK(( ratios[0] < 0.11 ));
+      CHECK(( 0.09 < ratios[1] )); CHECK(( ratios[1] < 0.11 ));
+      CHECK(( 0.09 < ratios[2] )); CHECK(( ratios[2] < 0.11 ));
+      CHECK(( 0.09 < ratios[3] )); CHECK(( ratios[3] < 0.11 ));
+      CHECK(( 0.09 < ratios[4] )); CHECK(( ratios[4] < 0.11 ));
+      CHECK(( 0.09 < ratios[5] )); CHECK(( ratios[5] < 0.11 ));
+      CHECK(( 0.09 < ratios[6] )); CHECK(( ratios[6] < 0.11 ));
+      CHECK(( 0.09 < ratios[7] )); CHECK(( ratios[7] < 0.11 ));
+      CHECK(( 0.09 < ratios[8] )); CHECK(( ratios[8] < 0.11 ));
+      CHECK(( 0.09 < ratios[9] )); CHECK(( ratios[9] < 0.11 ));
+      //CHECK( false );
+      }
+
+   SECTION("min is 10")
+      {
+      // 10–19
+      const size_t MIN = 10;
+      const size_t MAX = 20; // excluded
+      const size_t ITERATIONS = 10000;
+
+      std::vector<int> counts(MAX, 0);
+      std::vector<double> ratios(MAX, 1.0);
+
+      for (size_t i = 0; i < ITERATIONS; i++)
+         {
+         BigInt b = BigInt::random_integer(*rng, MIN, MAX);
+         size_t x = b.to_u32bit();
+         counts[x]++;
+         }
+
+      std::stringstream debug;
+      for (size_t d = MIN; d < MAX; ++d)
+         {
+         auto ratio = static_cast<double>(counts[d]) / ITERATIONS;
+         ratios[d] = ratio;
+
+         if (!debug.str().empty())
+            {
+            debug << ", ";
+            }
+         debug << d << ": " << std::setprecision(3) << ratio;
+         }
+
+      INFO( debug.str() )
+
+      // Have ~ 10 % on each digit from 10-19
+      CHECK(( 0.09 < ratios[10] )); CHECK(( ratios[10] < 0.11 ));
+      CHECK(( 0.09 < ratios[11] )); CHECK(( ratios[11] < 0.11 ));
+      CHECK(( 0.09 < ratios[12] )); CHECK(( ratios[12] < 0.11 ));
+      CHECK(( 0.09 < ratios[13] )); CHECK(( ratios[13] < 0.11 ));
+      CHECK(( 0.09 < ratios[14] )); CHECK(( ratios[14] < 0.11 ));
+      CHECK(( 0.09 < ratios[15] )); CHECK(( ratios[15] < 0.11 ));
+      CHECK(( 0.09 < ratios[16] )); CHECK(( ratios[16] < 0.11 ));
+      CHECK(( 0.09 < ratios[17] )); CHECK(( ratios[17] < 0.11 ));
+      CHECK(( 0.09 < ratios[18] )); CHECK(( ratios[18] < 0.11 ));
+      CHECK(( 0.09 < ratios[19] )); CHECK(( ratios[19] < 0.11 ));
+      //CHECK( false );
+      }
+   }
+
 #endif