Add pgm_array<T, N> as a bound-safe alternative to pgm_ptr<T>

See #2220

Author: bblanchon

src/ArduinoJson/Numbers/FloatParts.hpp

@@ -28,8 +28,8 @@ inline int16_t normalize(TFloat& value) {
 
   if (value >= ARDUINOJSON_POSITIVE_EXPONENTIATION_THRESHOLD) {
     for (; index >= 0; index--) {
-      if (value >= traits::positiveBinaryPowersOfTen()[index]) {
-        value *= traits::negativeBinaryPowersOfTen()[index];
+      if (value >= traits::positiveBinaryPowersOfTen()[uint8_t(index)]) {
+        value *= traits::negativeBinaryPowersOfTen()[uint8_t(index)];
         powersOf10 = int16_t(powersOf10 + bit);
       }
       bit >>= 1;
@@ -38,8 +38,8 @@ inline int16_t normalize(TFloat& value) {
 
   if (value > 0 && value <= ARDUINOJSON_NEGATIVE_EXPONENTIATION_THRESHOLD) {
     for (; index >= 0; index--) {
-      if (value < traits::negativeBinaryPowersOfTen()[index] * 10) {
-        value *= traits::positiveBinaryPowersOfTen()[index];
+      if (value < traits::negativeBinaryPowersOfTen()[uint8_t(index)] * 10) {
+        value *= traits::positiveBinaryPowersOfTen()[uint8_t(index)];
         powersOf10 = int16_t(powersOf10 - bit);
       }
       bit >>= 1;

src/ArduinoJson/Numbers/FloatTraits.hpp

@@ -29,7 +29,7 @@ struct FloatTraits<T, 8 /*64bits*/> {
   using exponent_type = int16_t;
   static const exponent_type exponent_max = 308;
 
-  static pgm_ptr<T> positiveBinaryPowersOfTen() {
+  static pgm_array<T, 9> positiveBinaryPowersOfTen() {
     ARDUINOJSON_DEFINE_PROGMEM_ARRAY(  //
         uint64_t, factors,
         {
@@ -43,10 +43,10 @@ struct FloatTraits<T, 8 /*64bits*/> {
             0x5A827748F9301D32,  // 1e128
             0x75154FDD7F73BF3C,  // 1e256
         });
-    return pgm_ptr<T>(reinterpret_cast<const T*>(factors));
+    return pgm_array<T, 9>(reinterpret_cast<const T*>(factors));
   }
 
-  static pgm_ptr<T> negativeBinaryPowersOfTen() {
+  static pgm_array<T, 9> negativeBinaryPowersOfTen() {
     ARDUINOJSON_DEFINE_PROGMEM_ARRAY(  //
         uint64_t, factors,
         {
@@ -60,7 +60,7 @@ struct FloatTraits<T, 8 /*64bits*/> {
             0x255BBA08CF8C979D,  // 1e-128
             0x0AC8062864AC6F43   // 1e-256
         });
-    return pgm_ptr<T>(reinterpret_cast<const T*>(factors));
+    return pgm_array<T, 9>(reinterpret_cast<const T*>(factors));
   }
 
   static T nan() {
@@ -113,7 +113,7 @@ struct FloatTraits<T, 4 /*32bits*/> {
   using exponent_type = int8_t;
   static const exponent_type exponent_max = 38;
 
-  static pgm_ptr<T> positiveBinaryPowersOfTen() {
+  static pgm_array<T, 6> positiveBinaryPowersOfTen() {
     ARDUINOJSON_DEFINE_PROGMEM_ARRAY(uint32_t, factors,
                                      {
                                          0x41200000,  // 1e1f
@@ -123,10 +123,10 @@ struct FloatTraits<T, 4 /*32bits*/> {
                                          0x5a0e1bca,  // 1e16f
                                          0x749dc5ae   // 1e32f
                                      });
-    return pgm_ptr<T>(reinterpret_cast<const T*>(factors));
+    return pgm_array<T, 6>(reinterpret_cast<const T*>(factors));
   }
 
-  static pgm_ptr<T> negativeBinaryPowersOfTen() {
+  static pgm_array<T, 6> negativeBinaryPowersOfTen() {
     ARDUINOJSON_DEFINE_PROGMEM_ARRAY(uint32_t, factors,
                                      {
                                          0x3dcccccd,  // 1e-1f
@@ -136,7 +136,7 @@ struct FloatTraits<T, 4 /*32bits*/> {
                                          0x24e69595,  // 1e-16f
                                          0x0a4fb11f   // 1e-32f
                                      });
-    return pgm_ptr<T>(reinterpret_cast<const T*>(factors));
+    return pgm_array<T, 6>(reinterpret_cast<const T*>(factors));
   }
 
   static T forge(uint32_t bits) {

src/ArduinoJson/Polyfills/pgmspace_generic.hpp

@@ -5,6 +5,7 @@
 #pragma once
 
 #include <ArduinoJson/Namespace.hpp>
+#include <ArduinoJson/Polyfills/assert.hpp>
 
 #if ARDUINOJSON_ENABLE_PROGMEM
 #  include <ArduinoJson/Polyfills/pgmspace.hpp>
@@ -64,4 +65,22 @@ class pgm_ptr {
   const T* ptr_;
 };
 
+template <typename T, size_t N>
+class pgm_array {
+ public:
+  explicit pgm_array(const T* ptr) : ptr_(ptr) {}
+
+  T operator[](size_t index) const {
+    ARDUINOJSON_ASSERT(index < N);
+    return ptr_[intptr_t(index)];
+  }
+
+  size_t size() const {
+    return N;
+  }
+
+ private:
+  pgm_ptr<T> ptr_;
+};
+
 ARDUINOJSON_END_PRIVATE_NAMESPACE