Fixed incorrect string comparison on some platforms (fixes #1198)

src/ArduinoJson/Polyfills/safe_strcmp.hpp

@@ -10,23 +10,23 @@
 
 namespace ARDUINOJSON_NAMESPACE {
 
-inline int8_t safe_strcmp(const char* a, const char* b) {
+inline int safe_strcmp(const char* a, const char* b) {
   if (a == b)
     return 0;
   if (!a)
     return -1;
   if (!b)
     return 1;
-  return static_cast<int8_t>(strcmp(a, b));
+  return strcmp(a, b);
 }
 
-inline int8_t safe_strncmp(const char* a, const char* b, size_t n) {
+inline int safe_strncmp(const char* a, const char* b, size_t n) {
   if (a == b)
     return 0;
   if (!a)
     return -1;
   if (!b)
     return 1;
-  return static_cast<int8_t>(strncmp(a, b, n));
+  return strncmp(a, b, n);
 }
 }  // namespace ARDUINOJSON_NAMESPACE

src/ArduinoJson/Strings/ArduinoStringAdapter.hpp

@@ -31,7 +31,7 @@ class ArduinoStringAdapter {
     return !_str->c_str();
   }
 
-  int8_t compare(const char* other) const {
+  int compare(const char* other) const {
     // Arduino's String::c_str() can return NULL
     const char* me = _str->c_str();
     return safe_strcmp(me, other);

src/ArduinoJson/Strings/ConstRamStringAdapter.hpp

@@ -17,7 +17,7 @@ class ConstRamStringAdapter {
  public:
   ConstRamStringAdapter(const char* str = 0) : _str(str) {}
 
-  int8_t compare(const char* other) const {
+  int compare(const char* other) const {
     return safe_strcmp(_str, other);
   }
 

src/ArduinoJson/Strings/FlashStringAdapter.hpp

@@ -15,14 +15,14 @@ class FlashStringAdapter {
  public:
   FlashStringAdapter(const __FlashStringHelper* str) : _str(str) {}
 
-  int8_t compare(const char* other) const {
+  int compare(const char* other) const {
     if (!other && !_str)
       return 0;
     if (!_str)
       return -1;
     if (!other)
       return 1;
-    return int8_t(-strcmp_P(other, reinterpret_cast<const char*>(_str)));
+    return -strcmp_P(other, reinterpret_cast<const char*>(_str));
   }
 
   bool equals(const char* expected) const {

src/ArduinoJson/Strings/SizedFlashStringAdapter.hpp

@@ -15,15 +15,14 @@ class SizedFlashStringAdapter {
   SizedFlashStringAdapter(const __FlashStringHelper* str, size_t sz)
       : _str(str), _size(sz) {}
 
-  int8_t compare(const char* other) const {
+  int compare(const char* other) const {
     if (!other && !_str)
       return 0;
     if (!_str)
       return -1;
     if (!other)
       return 1;
-    return int8_t(
-        -strncmp_P(other, reinterpret_cast<const char*>(_str), _size));
+    return -strncmp_P(other, reinterpret_cast<const char*>(_str), _size);
   }
 
   bool equals(const char* expected) const {

src/ArduinoJson/Strings/SizedRamStringAdapter.hpp

@@ -16,8 +16,8 @@ class SizedRamStringAdapter {
  public:
   SizedRamStringAdapter(const char* str, size_t n) : _str(str), _size(n) {}
 
-  int8_t compare(const char* other) const {
-    return safe_strncmp(_str, other, _size) == 0;
+  int compare(const char* other) const {
+    return safe_strncmp(_str, other, _size);
   }
 
   bool equals(const char* expected) const {

src/ArduinoJson/Strings/StlStringAdapter.hpp

@@ -30,10 +30,10 @@ class StlStringAdapter {
     return false;
   }
 
-  int8_t compare(const char* other) const {
+  int compare(const char* other) const {
     if (!other)
       return 1;
-    return static_cast<int8_t>(_str->compare(other));
+    return _str->compare(other);
   }
 
   bool equals(const char* expected) const {