fix: 默认使用单精度浮点，节约flash空间，抄自 stm32duino/Arduino_Core_STM32#2036

Author: chenxuuu

Diff for: cores/AirMCU/Print.cpp

@@ -129,6 +129,11 @@ size_t Print::print(unsigned long long n, int base)
   }
 }
 
+size_t Print::print(float n, int digits)
+{
+  return printFloat(n, digits);
+}
+
 size_t Print::print(double n, int digits)
 {
   return printFloat(n, digits);
@@ -221,6 +226,13 @@ size_t Print::println(unsigned long long num, int base)
   return n;
 }
 
+size_t Print::println(float num, int digits)
+{
+  size_t n = print(num, digits);
+  n += println();
+  return n;
+}
+
 size_t Print::println(double num, int digits)
 {
   size_t n = print(num, digits);
@@ -406,7 +418,8 @@ size_t Print::printULLNumber(unsigned long long n64, uint8_t base)
   return bytes;
 }
 
-size_t Print::printFloat(double number, uint8_t digits)
+template <class T>
+size_t Print::printFloat(T number, uint8_t digits)
 {
   size_t n = 0;
 
@@ -430,7 +443,7 @@ size_t Print::printFloat(double number, uint8_t digits)
   }
 
   // Round correctly so that print(1.999, 2) prints as "2.00"
-  double rounding = 0.5;
+  T rounding = 0.5;
   for (uint8_t i = 0; i < digits; ++i) {
     rounding /= 10.0;
   }
@@ -439,7 +452,7 @@ size_t Print::printFloat(double number, uint8_t digits)
 
   // Extract the integer part of the number and print it
   unsigned long int_part = (unsigned long)number;
-  double remainder = number - (double)int_part;
+  T remainder = number - (T)int_part;
   n += print(int_part);
 
   // Print the decimal point, but only if there are digits beyond

Diff for: cores/AirMCU/Print.h

@@ -36,7 +36,8 @@ class Print {
     int write_error;
     size_t printNumber(unsigned long, uint8_t);
     size_t printULLNumber(unsigned long long, uint8_t);
-    size_t printFloat(double, uint8_t);
+    template <class T>
+    size_t printFloat(T, uint8_t);
   protected:
     void setWriteError(int err = 1)
     {
@@ -86,6 +87,7 @@ class Print {
     size_t print(unsigned long, int = DEC);
     size_t print(long long, int = DEC);
     size_t print(unsigned long long, int = DEC);
+    size_t print(float, int = 2);
     size_t print(double, int = 2);
     size_t print(const Printable &);
 
@@ -100,6 +102,7 @@ class Print {
     size_t println(unsigned long, int = DEC);
     size_t println(long long, int = DEC);
     size_t println(unsigned long long, int = DEC);
+    size_t println(float, int = 2);
     size_t println(double, int = 2);
     size_t println(const Printable &);
     size_t println(void);

Diff for: platform.txt

@@ -31,9 +31,9 @@ compiler.extra_flags=-mcpu={build.mcu} {build.fpu} {build.float-abi} -DUSE_FULL_
 # 汇编编译器参数
 compiler.S.flags={compiler.extra_flags} -c -x assembler-with-cpp {compiler.air.extra_include}
 
-compiler.c.flags={compiler.extra_flags} -c {build.flags.optimize} {build.flags.debug} {compiler.warning_flags} -std={compiler.c.std} -ffunction-sections -fdata-sections --param max-inline-insns-single=500 -MMD {compiler.air.extra_include}
+compiler.c.flags={compiler.extra_flags} -c {build.flags.optimize} {build.flags.debug} {compiler.warning_flags} -std={compiler.c.std} -fsingle-precision-constant -ffunction-sections -fdata-sections --param max-inline-insns-single=500 -MMD {compiler.air.extra_include}
 
-compiler.cpp.flags={compiler.extra_flags} -c {build.flags.optimize} {build.flags.debug} {compiler.warning_flags} -std={compiler.cpp.std} -ffunction-sections -fdata-sections -fno-threadsafe-statics --param max-inline-insns-single=500 -fno-rtti -fno-exceptions -fno-use-cxa-atexit -MMD {compiler.air.extra_include}
+compiler.cpp.flags={compiler.extra_flags} -c {build.flags.optimize} {build.flags.debug} {compiler.warning_flags} -std={compiler.cpp.std} -fsingle-precision-constant -ffunction-sections -fdata-sections -fno-threadsafe-statics --param max-inline-insns-single=500 -fno-rtti -fno-exceptions -fno-use-cxa-atexit -MMD {compiler.air.extra_include}
 
 compiler.ar.flags=rcs