Regards issue mpaland#118:

* Added comment explaining how we "narrowly escape" undefined behavior with our `NTOA_ABS()` macro.
* Added checks for printing extremal values of the various signed and unsigned integer types, just in case.

printf.c

@@ -132,6 +132,9 @@ typedef uint8_t numeric_base_t;
 #include <float.h>
 #endif
 
+// Note in particular the behavior here on LONG_MIN or LLONG_MIN; it is valid
+// and well-defined, but if you're not careful you can easily trigger undefined
+// behavior with -LONG_MIN or -LLONG_MIN
 #define NTOA_ABS(_x) ( (_x) > 0 ? (NTOA_VALUE_TYPE)(_x) : -((NTOA_VALUE_TYPE)_x) )
 
 // output function type

test/test_suite.cpp

@@ -33,7 +33,7 @@
 #include <string.h>
 #include <sstream>
 #include <math.h>
-
+#include <limits>
 
 namespace test {
   // use functions in own test namespace to avoid stdio conflicts
@@ -1055,6 +1055,59 @@ TEST_CASE("misc", "[]" ) {
 #endif
 }
 
+TEST_CASE("extremal signed integer values", "[]" ) {
+  char buffer[100];
+  char expected[100];
+
+  std::sprintf(expected, "%hhd", std::numeric_limits<char>::max());
+  PRINTING_CHECK(expected, ==, test::sprintf_, buffer, "%hhd", std::numeric_limits<char>::max());
+
+  std::sprintf(expected, "%hd", std::numeric_limits<short int>::max());
+  PRINTING_CHECK(expected, ==, test::sprintf_, buffer, "%hd", std::numeric_limits<short int>::max());
+
+  std::sprintf(expected, "%hd", std::numeric_limits<short int>::max());
+  PRINTING_CHECK(expected, ==, test::sprintf_, buffer, "%hd", std::numeric_limits<short int>::max());
+
+  std::sprintf(expected, "%d", std::numeric_limits<int>::min());
+  PRINTING_CHECK(expected, ==, test::sprintf_, buffer, "%d", std::numeric_limits<int>::min());
+
+  std::sprintf(expected, "%d", std::numeric_limits<int>::max());
+  PRINTING_CHECK(expected, ==, test::sprintf_, buffer, "%d", std::numeric_limits<int>::max());
+
+  std::sprintf(expected, "%ld", std::numeric_limits<long int>::min());
+  PRINTING_CHECK(expected, ==, test::sprintf_, buffer, "%ld", std::numeric_limits<long int>::min());
+
+  std::sprintf(expected, "%ld", std::numeric_limits<long int>::max());
+  PRINTING_CHECK(expected, ==, test::sprintf_, buffer, "%ld", std::numeric_limits<long int>::max());
+
+  std::sprintf(expected, "%lld", std::numeric_limits<long long int>::min());
+  PRINTING_CHECK(expected, ==, test::sprintf_, buffer, "%lld", std::numeric_limits<long long int>::min());
+
+  std::sprintf(expected, "%lld", std::numeric_limits<long long int>::max());
+  PRINTING_CHECK(expected, ==, test::sprintf_, buffer, "%lld", std::numeric_limits<long long int>::max());
+}
+
+TEST_CASE("extremal unsigned integer values", "[]" ) {
+  char buffer[100];
+  char expected[100];
+
+  std::sprintf(expected, "%hhu", std::numeric_limits<char unsigned>::max());
+  PRINTING_CHECK(expected, ==, test::sprintf_, buffer, "%hhu", std::numeric_limits<char unsigned>::max());
+
+  std::sprintf(expected, "%hu", std::numeric_limits<short unsigned>::max());
+  PRINTING_CHECK(expected, ==, test::sprintf_, buffer, "%hu", std::numeric_limits<short unsigned>::max());
+
+  std::sprintf(expected, "%u", std::numeric_limits<unsigned>::max());
+  PRINTING_CHECK(expected, ==, test::sprintf_, buffer, "%u", std::numeric_limits<unsigned>::max());
+
+  std::sprintf(expected, "%lu", std::numeric_limits<long unsigned>::max());
+  PRINTING_CHECK(expected, ==, test::sprintf_, buffer, "%lu", std::numeric_limits<long unsigned>::max());
+
+  std::sprintf(expected, "%llu", std::numeric_limits<long long unsigned>::max());
+  PRINTING_CHECK(expected, ==, test::sprintf_, buffer, "%llu", std::numeric_limits<long long unsigned>::max());
+}
+
+
 #ifdef TEST_WITH_NON_STANDARD_FORMAT_STRINGS
 DISABLE_WARNING_POP
 #endif