fix(printf): fixed support of NaN

(hot) fixes #37

README.md

@@ -28,7 +28,7 @@ Therefore I decided to write an own, final implementation which meets the follow
  - Support of decimal/floating number representation (with an own fast itoa/ftoa)
  - Reentrant and thread-safe, malloc free, no static vars/buffers
  - LINT and compiler L4 warning free, mature, coverity clean, automotive ready
- - Extensive test suite (> 350 test cases) passing
+ - Extensive test suite (> 370 test cases) passing
  - Simply the best *printf* around the net
  - MIT license
 

printf.c

@@ -311,6 +311,14 @@ static size_t _ftoa(out_fct_type out, char* buffer, size_t idx, size_t maxlen, d
   // powers of 10
   static const double pow10[] = { 1, 10, 100, 1000, 10000, 100000, 1000000, 10000000, 100000000, 1000000000 };
 
+  // test for NaN
+  if (value != value) {
+    out('n', buffer, idx++, maxlen);
+    out('a', buffer, idx++, maxlen);
+    out('n', buffer, idx++, maxlen);
+    return idx;
+  }
+
   // test for negative
   bool negative = false;
   if (value < 0) {
@@ -341,8 +349,10 @@ static size_t _ftoa(out_fct_type out, char* buffer, size_t idx, size_t maxlen, d
       ++whole;
     }
   }
-  else if ((diff == 0.5) && ((frac == 0U) || (frac & 1U))) {
+  else if (diff < 0.5) {
-    // if halfway, round up if odd, OR if last digit is 0
+  }
+  else if ((frac == 0U) || (frac & 1U)) {
+    // if halfway, round up if odd OR if last digit is 0
     ++frac;
   }
 

test/test_suite.cpp

@@ -31,6 +31,7 @@
 #include "catch.hpp"
 
 #include <string.h>
+#include <math.h>
 
 namespace test {
   // use functions in own test namespace to avoid stdio conflicts
@@ -1019,6 +1020,9 @@ TEST_CASE("length", "[]" ) {
 TEST_CASE("float", "[]" ) {
   char buffer[100];
 
+  test::sprintf(buffer, "%.4f", NAN);   // using the NAN macro of math.h
+  REQUIRE(!strcmp(buffer, "nan"));
+
   test::sprintf(buffer, "%.4f", 3.1415354);
   REQUIRE(!strcmp(buffer, "3.1415"));