stdlib_noniso.cpp: Handle rounding corner case for dtostrf

Rounding must be done before separating the integral and decimal portions.

Author: eriknyquist

cores/arduino/WString.cpp

@@ -138,7 +138,7 @@ String::String(float value, unsigned char decimalPlaces)
 
 	if(decimalPlaces)  totalSize += 1 + ((int)decimalPlaces & 0x0FF);
 
-	char buf[totalSize+1];
+	char buf[totalSize + 2];
 	*this = dtostrf(value, 0, decimalPlaces, buf);
 }
 
@@ -149,7 +149,7 @@ String::String(double value, unsigned char decimalPlaces)
 
 	if(decimalPlaces)  totalSize += 1 + ((int)decimalPlaces & 0x0FF);
 
-	char buf[totalSize+1];
+	char buf[totalSize + 2];
 	*this = dtostrf(value, 0, decimalPlaces, buf);
 }
 

cores/arduino/stdlib_noniso.cpp

@@ -215,6 +215,12 @@ char *dtostrf(double number, signed char width, unsigned char prec, char *s)
       number = -number;
     }
 
+    // rounding up to the precision
+    rounding = 0.5;
+    for (i = 0; i < prec; ++i)
+        rounding /= 10.0;
+    number += rounding;
+
     // seperate integral and fractional parts
     integer = (unsigned long long) number;
     fraction = (double) (number - integer);
@@ -231,12 +237,6 @@ char *dtostrf(double number, signed char width, unsigned char prec, char *s)
     out += before;
     if (!prec) goto end;
 
-    // rounding up to the precision
-    rounding = 0.5;
-    for (i = 0; i < prec; ++i)
-        rounding /= 10.0;
-    fraction += rounding;
-
     // generate chars for each digit of the fractional part
     *out++ = '.';
     for (i = 0; i < prec; ++i) {