Creating More Accuracy in NS_TO_S

include/rcutils/time.h

@@ -49,6 +49,69 @@ typedef int64_t rcutils_time_point_value_t;
 /// A duration of time, measured in nanoseconds.
 typedef int64_t rcutils_duration_value_t;
 
+/**
+ * This function returns an accurate conversion from nanoseconds to seconds.
+ *
+ * The nanoseconds argument has to be an int64_t to ensure exact division
+ *
+ * <hr>
+ * Attribute          | Adherence
+ * ------------------ | -------------
+ * Allocates Memory   | No
+ * Thread-Safe        | Yes
+ * Uses Atomics       | No
+ * Lock-Free          | Yes
+ *
+ * \param[in] nanoseconds The int64_t needed for conversion
+ * \return double That nanoseconds number as seconds.
+ */
+RCUTILS_PUBLIC
+RCUTILS_WARN_UNUSED
+double
+rcutils_nanoseconds_to_seconds(const int64_t nanoseconds);
+
+/**
+ * This function returns an accurate conversion from nanoseconds to milliseconds.
+ *
+ * The nanoseconds argument has to be an int64_t to ensure exact division
+ *
+ * <hr>
+ * Attribute          | Adherence
+ * ------------------ | -------------
+ * Allocates Memory   | No
+ * Thread-Safe        | Yes
+ * Uses Atomics       | No
+ * Lock-Free          | Yes
+ *
+ * \param[in] nanoseconds The int64_t needed for conversion
+ * \return double That nanoseconds number as milliseconds.
+ */
+RCUTILS_PUBLIC
+RCUTILS_WARN_UNUSED
+double
+rcutils_nanoseconds_to_milliseconds(const int64_t nanoseconds);
+
+/**
+ * This function returns an accurate conversion from nanoseconds to microseconds.
+ *
+ * The nanoseconds argument has to be an int64_t to ensure exact division
+ *
+ * <hr>
+ * Attribute          | Adherence
+ * ------------------ | -------------
+ * Allocates Memory   | No
+ * Thread-Safe        | Yes
+ * Uses Atomics       | No
+ * Lock-Free          | Yes
+ *
+ * \param[in] nanoseconds The int64_t needed for conversion
+ * \return double That nanoseconds number as microseconds.
+ */
+RCUTILS_PUBLIC
+RCUTILS_WARN_UNUSED
+double
+rcutils_nanoseconds_to_microseconds(const int64_t nanoseconds);
+
 /**
  * This function returns the time from a system clock.
  * The closest equivalent would be to std::chrono::system_clock::now();

src/time.c

@@ -28,6 +28,48 @@ extern "C"
 #include "rcutils/error_handling.h"
 #include "rcutils/snprintf.h"
 
+double
+rcutils_nanoseconds_to_seconds(const int64_t nanoseconds)
+{
+  // scale the nanoseconds separately for improved accuracy
+  int64_t sec, nsec;
+  nsec = (nanoseconds % 1000000000l);
+  sec = ((nanoseconds - nsec) / 1000000000l);
+
+  double sec_double, nsec_double;
+  nsec_double = 1e-9 * (double)(nsec);
+  sec_double = (double)(sec);
+  return sec_double + nsec_double;
+}
+
+double
+rcutils_nanoseconds_to_milliseconds(const int64_t nanoseconds)
+{
+  // scale the nanoseconds separately for improved accuracy
+  int64_t sec, nsec;
+  nsec = (nanoseconds % 1000000l);
+  sec = ((nanoseconds - nsec) / 1000000l);
+
+  double sec_double, nsec_double;
+  nsec_double = 1e-6 * (double)(nsec);
+  sec_double = (double)(sec);
+  return sec_double + nsec_double;
+}
+
+double
+rcutils_nanoseconds_to_microseconds(const int64_t nanoseconds)
+{
+  // scale the nanoseconds separately for improved accuracy
+  int64_t sec, nsec;
+  nsec = (nanoseconds % 1000l);
+  sec = ((nanoseconds - nsec) / 1000l);
+
+  double sec_double, nsec_double;
+  nsec_double = 1e-3 * (double)(nsec);
+  sec_double = (double)(sec);
+  return sec_double + nsec_double;
+}
+
 rcutils_ret_t
 rcutils_time_point_value_as_nanoseconds_string(
   const rcutils_time_point_value_t * time_point,

test/test_time.cpp

@@ -121,6 +121,36 @@ TEST_F(TestTimeFixture, test_rcutils_time_conversion_macros) {
     9007199254740.992);  // maximum precision double (53 bits)
 }
 
+// Tests the rcutils time unit conversion functions.
+TEST_F(TestTimeFixture, test_rcutils_time_conversion_functions) {
+  // nanoseconds to seconds
+  EXPECT_EQ(rcutils_nanoseconds_to_seconds(1000000000ll), 1.0);  // int64_t
+  EXPECT_EQ(rcutils_nanoseconds_to_seconds(1000000042ll), 1.000000042);  // int64_t
+  EXPECT_EQ(rcutils_nanoseconds_to_seconds(-2999999999ll), -2.999999999);  // int64_t
+  EXPECT_EQ(rcutils_nanoseconds_to_seconds(1 + 1), 0.000000002);  // sum of two int64_ts
+  EXPECT_EQ(
+    rcutils_nanoseconds_to_seconds(9007199254740992),
+    9007199.254740992);  // maximum precision double as an int64_t
+
+  // nanoseconds to milliseconds
+  EXPECT_EQ(rcutils_nanoseconds_to_milliseconds(1000000ll), 1.0);  // int64_t
+  EXPECT_EQ(rcutils_nanoseconds_to_milliseconds(1000042ll), 1.000042);  // int64_t
+  EXPECT_EQ(rcutils_nanoseconds_to_milliseconds(-2999999ll), -2.999999);  // int64_t
+  EXPECT_EQ(rcutils_nanoseconds_to_milliseconds(1 + 1), 0.000002);  // sum of int64_ts
+  EXPECT_EQ(
+    rcutils_nanoseconds_to_milliseconds(9007199254740992),
+    9007199254.740992);  // maximum precision double as an int64_t
+
+  // nanoseconds to microseconds
+  EXPECT_EQ(rcutils_nanoseconds_to_microseconds(1000ll), 1.0);  // int64_t
+  EXPECT_EQ(rcutils_nanoseconds_to_microseconds(1042ll), 1.042);  // int64_t
+  EXPECT_EQ(rcutils_nanoseconds_to_microseconds(-2999ll), -2.999);  // int64_t
+  EXPECT_EQ(rcutils_nanoseconds_to_microseconds(1 + 1), 0.002);  // sum of int64_ts
+  EXPECT_EQ(
+    rcutils_nanoseconds_to_microseconds(9007199254740992),
+    9007199254740.992);  // maximum precision double as an int64_t
+}
+
 // Tests the rcutils_system_time_now() function.
 TEST_F(TestTimeFixture, test_rcutils_system_time_now) {
   rcutils_ret_t ret;