fixing / improving printFloat() from Mikal Hart

hardware/cores/arduino/Print.cpp

@@ -81,7 +81,7 @@ void Print::print(long n, int base)
 
 void Print::print(double n)
 {
-  printFloat(n*100, 2);
+  printFloat(n, 2);
 }
 
 void Print::println(void)
@@ -167,20 +167,37 @@ void Print::printNumber(unsigned long n, uint8_t base)
       'A' + buf[i - 1] - 10));
 }
 
-void Print::printFloat(double number, uint8_t scale) 
+void Print::printFloat(double number, uint8_t digits) 
 { 
-  double mult = pow(10,scale); 
-  double rounded = floor(number /mult); 
-  double biground = rounded * mult; 
-  double remainder = (number - biground);  
-  remainder = remainder / mult; 
-  print(long(rounded)); 
-  print("."); 
+  // Handle negative numbers
+  if (number < 0.0)
+  {
+     print('-');
+     number = -number;
+  }
 
-  while (scale--) {  
-    double toPrint = floor(remainder * 10); 
-    print(int(toPrint)); 
-    remainder -= (toPrint/10); 
-    remainder *= 10; 
+  // Round correctly so that print(1.999, 2) prints as "2.00"
+  double rounding = 0.5;
+  for (uint8_t i=0; i<digits; ++i)
+    rounding /= 10.0;
+  
+  number += rounding;
+
+  // Extract the integer part of the number and print it
+  unsigned long int_part = (unsigned long)number;
+  double remainder = number - (double)int_part;
+  print(int_part);
+
+  // Print the decimal point, but only if there are digits beyond
+  if (digits > 0)
+    print("."); 
+
+  // Extract digits from the remainder one at a time
+  while (digits-- > 0)
+  {
+    remainder *= 10.0;
+    int toPrint = int(remainder);
+    print(toPrint);
+    remainder -= toPrint; 
   } 
-} 
+}