move random int to cpp

cpp/open3d/utility/Random.cpp

@@ -26,6 +26,8 @@
 
 #include "open3d/utility/Random.h"
 
+#include "open3d/utility/Logging.h"
+
 namespace open3d {
 namespace utility {
 
@@ -47,5 +49,22 @@ RandomGlobalContext::RandomGlobalContext() {
     Seed(rd());
 }
 
+RandIntGenerator::RandIntGenerator(const int low, const int high)
+    : distribution_(low, high) {
+    if (low < 0) {
+        utility::LogError("low must be > 0, but got {}.", low);
+    }
+    if (low >= high) {
+        utility::LogError("low must be < high, but got low={} and high={}.",
+                          low, high);
+    }
+}
+
+int RandIntGenerator::operator()() {
+    std::lock_guard<std::mutex> lock(
+            *RandomGlobalContext::GetInstance().GetMutex());
+    return distribution_(*RandomGlobalContext::GetInstance().GetEngine());
+}
+
 }  // namespace utility
 }  // namespace open3d

cpp/open3d/utility/Random.h

@@ -68,13 +68,14 @@ class RandomGlobalContext {
 /// from a uniform distribution
 class RandIntGenerator {
 public:
-    RandIntGenerator(const int min, const int max) : distribution_(min, max) {}
+    /// Generate uniformly distributed random integer from
+    /// [low, low + 1, ... high - 1].
+    ///
+    /// \param low The lower bound (inclusive). \p low must be >= 0.
+    /// \param high The upper bound (exclusive). \p high must be > \p low.
+    RandIntGenerator(const int low, const int high);
 
-    int operator()() {
-        std::lock_guard<std::mutex> lock(
-                *RandomGlobalContext::GetInstance().GetMutex());
-        return distribution_(*RandomGlobalContext::GetInstance().GetEngine());
-    }
+    int operator()();
 
 protected:
     std::uniform_int_distribution<int> distribution_;