diff --git a/cores/esp8266/FS.cpp b/cores/esp8266/FS.cpp
index 7a13dcede8..125ac527cb 100644
--- a/cores/esp8266/FS.cpp
+++ b/cores/esp8266/FS.cpp
@@ -144,6 +144,14 @@ String Dir::fileName() {
     return _impl->fileName();
 }
 
+size_t Dir::fileSize() {
+    if (!_impl) {
+        return 0;
+    }
+
+    return _impl->fileSize();
+}
+
 bool Dir::next() {
     if (!_impl) {
         return false;
diff --git a/cores/esp8266/FS.h b/cores/esp8266/FS.h
index 3158fd5290..d8d8dedd72 100644
--- a/cores/esp8266/FS.h
+++ b/cores/esp8266/FS.h
@@ -78,6 +78,7 @@ class Dir {
 
     File openFile(const char* mode);
     String fileName();
+    size_t fileSize();
     bool next();
 
 protected:
diff --git a/cores/esp8266/FSImpl.h b/cores/esp8266/FSImpl.h
index 8e48a9fda0..20d886e764 100644
--- a/cores/esp8266/FSImpl.h
+++ b/cores/esp8266/FSImpl.h
@@ -56,6 +56,7 @@ class DirImpl {
     virtual ~DirImpl() { }
     virtual FileImplPtr openFile(OpenMode openMode, AccessMode accessMode) = 0;
     virtual const char* fileName() = 0;
+    virtual size_t fileSize() = 0;
     virtual bool next() = 0;
 };
 
diff --git a/cores/esp8266/core_esp8266_noniso.c b/cores/esp8266/core_esp8266_noniso.c
index 40fe5e6dd4..d5b9d82f28 100644
--- a/cores/esp8266/core_esp8266_noniso.c
+++ b/cores/esp8266/core_esp8266_noniso.c
@@ -148,7 +148,8 @@ char* ultoa(unsigned long value, char* result, int base) {
 }
 
 char * dtostrf(double number, signed char width, unsigned char prec, char *s) {
-
+    bool negative = false;
+    
     if (isnan(number)) {
         strcpy(s, "nan");
         return s;
@@ -158,50 +159,65 @@ char * dtostrf(double number, signed char width, unsigned char prec, char *s) {
         return s;
     }
 
-    if (number > 4294967040.0 || number < -4294967040.0) {
-        strcpy(s, "ovf");
-        return s;
-    }
-
     char* out = s;
-    int signInt_Part = 1;
-
+   
+    int fillme = width; // how many cells to fill for the integer part
+    if (prec > 0) {
+        fillme -= (prec+1);
+    } 
+   
     // Handle negative numbers
     if (number < 0.0) {
-        signInt_Part = -1;
+        negative = true;
+        fillme--;
         number = -number;
     }
 
-    // calc left over digits 
-    if (prec > 0)
-    {
-        width -= (prec + 1);
-    }
-
     // Round correctly so that print(1.999, 2) prints as "2.00"
-    double rounding = 0.5;
+    // I optimized out most of the divisions
+    double rounding = 2.0;
     for (uint8_t i = 0; i < prec; ++i)
-        rounding /= 10.0;
+        rounding *= 10.0;     
+    rounding = 1.0 / rounding; 
 
     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;
-    out += sprintf(out, "%*ld", width, int_part * signInt_Part);
-
-    // Print the decimal point, but only if there are digits beyond
-    if (prec > 0) {
-        *out = '.';
-        ++out;
-
-
-        for (unsigned char decShift = prec; decShift > 0; decShift--) {
-            remainder *= 10.0;
-        }
-        sprintf(out, "%0*d", prec, (int)remainder);
+   
+    // Figure out how big our number really is
+    double tenpow = 1.0;
+    int digitcount = 1;
+    while (number >= 10.0 * tenpow) {
+        tenpow *= 10.0;   
+        digitcount++;
+    }
+   
+    number /= tenpow;
+    fillme -= digitcount;
+   
+    // Pad unused cells with spaces
+    while (fillme-- > 0) {
+        *out++ = ' ';
+    }
+    
+    // Handle negative sign
+    if (negative) *out++ = '-';
+   
+    // Print the digits, and if necessary, the decimal point
+    digitcount += prec;
+    int8_t digit = 0;
+    while (digitcount-- > 0) {       
+        digit = (int8_t)number;
+        if (digit > 9) digit = 9; // insurance
+        *out++ = (char)('0' | digit);
+        if ((digitcount == prec) && (prec > 0)) {
+            *out++ = '.';
+        }   
+        number -= digit;
+        number *= 10.0;
     }
 
+    // make sure the string is terminated
+    *out = 0;
     return s;
 }
 
+
diff --git a/cores/esp8266/spiffs_api.cpp b/cores/esp8266/spiffs_api.cpp
index 157ae86bcd..d9c7c618f4 100644
--- a/cores/esp8266/spiffs_api.cpp
+++ b/cores/esp8266/spiffs_api.cpp
@@ -308,6 +308,13 @@ class SPIFFSDirImpl : public DirImpl {
         return (const char*) _dirent.name;
     }
 
+    size_t fileSize() override {
+        if (!_valid)
+            return 0;
+
+        return _dirent.size;
+    }
+
     bool next() override {
         spiffs_dirent* result = SPIFFS_readdir(&_dir, &_dirent);
         _valid = (result != nullptr);