Add rounding functions for chrono durations and timepoints.

Author: AnthonyCalandra

CPP17.md

@@ -39,6 +39,7 @@ C++17 includes the following new library features:
 - [gcd and lcm](#gcd-and-lcm)
 - [std::not_fn](#stdnot_fn)
 - [string conversion to/from numbers](#string-conversion-tofrom-numbers)
+- [rounding functions for chrono durations and timepoints](#rounding-functions-for-chrono-durations-and-timepoints)
 
 ## C++17 Language Features
 
@@ -686,6 +687,17 @@ if (ec == std::errc{}) { std::cout << n << std::endl; } // 123
 else { /* handle failure */ }
 ```
 
+### Rounding functions for chrono durations and timepoints
+Provides abs, round, ceil, and floor helper functions for `std::chrono::duration` and `std::chrono::time_point`.
+```c++
+using seconds = std::chrono::seconds;
+std::chrono::milliseconds d{ 5500 };
+std::chrono::abs(d); // == 5s
+std::chrono::round<seconds>(d); // == 6s
+std::chrono::ceil<seconds>(d); // == 6s
+std::chrono::floor<seconds>(d); // == 5s
+```
+
 ## Acknowledgements
 * [cppreference](http://en.cppreference.com/w/cpp) - especially useful for finding examples and documentation of new library features.
 * [C++ Rvalue References Explained](http://web.archive.org/web/20240324121501/http://thbecker.net/articles/rvalue_references/section_01.html) - a great introduction I used to understand rvalue references, perfect forwarding, and move semantics.

README.md

@@ -70,6 +70,7 @@ C++17 includes the following new library features:
 - [gcd and lcm](#gcd-and-lcm)
 - [std::not_fn](#stdnot_fn)
 - [string conversion to/from numbers](#string-conversion-tofrom-numbers)
+- [rounding functions for chrono durations and timepoints](#rounding-functions-for-chrono-durations-and-timepoints)
 
 C++14 includes the following new language features:
 - [binary literals](#binary-literals)
@@ -1360,6 +1361,17 @@ if (ec == std::errc{}) { std::cout << n << std::endl; } // 123
 else { /* handle failure */ }
 ```
 
+### Rounding functions for chrono durations and timepoints
+Provides abs, round, ceil, and floor helper functions for `std::chrono::duration` and `std::chrono::time_point`.
+```c++
+using seconds = std::chrono::seconds;
+std::chrono::milliseconds d{ 5500 };
+std::chrono::abs(d); // == 5s
+std::chrono::round<seconds>(d); // == 6s
+std::chrono::ceil<seconds>(d); // == 6s
+std::chrono::floor<seconds>(d); // == 5s
+```
+
 ## C++14 Language Features
 
 ### Binary literals