1 files changed, 17 insertions, 12 deletions

diff --git a/py/formatfloat.c b/py/formatfloat.c
index 9ff80d9f63..35cd5d51af 100644
--- a/py/formatfloat.c
+++ b/py/formatfloat.c
@@ -1,5 +1,5 @@
 /*
- * This file is part of the Micro Python project, http://micropython.org/
+ * This file is part of the MicroPython project, http://micropython.org/
  *
  * The MIT License (MIT)
  *
@@ -118,7 +118,7 @@ int mp_format_float(FPTYPE f, char *buf, size_t buf_size, char fmt, int prec, ch
             *s++ = '?';
         }
         if (buf_size >= 1) {
-            *s++ = '\0';
+            *s = '\0';
         }
         return buf_size >= 2;
     }
@@ -161,7 +161,7 @@ int mp_format_float(FPTYPE f, char *buf, size_t buf_size, char fmt, int prec, ch
     if (fmt == 'g' && prec == 0) {
         prec = 1;
     }
-    int e, e1; 
+    int e, e1;
     int dec = 0;
     char e_sign = '\0';
     int num_digits = 0;
@@ -209,7 +209,7 @@ int mp_format_float(FPTYPE f, char *buf, size_t buf_size, char fmt, int prec, ch
                 e_sign_char = '+';
             }
         } else if (fp_isless1(f)) {
-            e++; 
+            e++;
             f *= FPCONST(10.0);
         }
 
@@ -232,7 +232,7 @@ int mp_format_float(FPTYPE f, char *buf, size_t buf_size, char fmt, int prec, ch
 
             num_digits = prec;
             if (num_digits) {
-                *s++ = '.'; 
+                *s++ = '.';
                 while (--e && num_digits) {
                     *s++ = '0';
                     num_digits--;
@@ -266,7 +266,7 @@ int mp_format_float(FPTYPE f, char *buf, size_t buf_size, char fmt, int prec, ch
             f *= FPCONST(0.1);
         }
 
-        // If the user specified fixed format (fmt == 'f') and e makes the 
+        // If the user specified fixed format (fmt == 'f') and e makes the
         // number too big to fit into the available buffer, then we'll
         // switch to the 'e' format.
 
@@ -327,12 +327,12 @@ int mp_format_float(FPTYPE f, char *buf, size_t buf_size, char fmt, int prec, ch
         if (prec == 0) {
             prec = 1;
         }
-        num_digits = prec; 
+        num_digits = prec;
     }
 
     // Print the digits of the mantissa
     for (int i = 0; i < num_digits; ++i, --dec) {
-        int32_t d = f;
+        int32_t d = (int32_t)f;
         *s++ = '0' + d;
         if (dec == 0 && prec > 0) {
             *s++ = '.';
@@ -365,7 +365,7 @@ int mp_format_float(FPTYPE f, char *buf, size_t buf_size, char fmt, int prec, ch
             if (rs == buf) {
                 break;
             }
-            rs--; 
+            rs--;
         }
         if (*rs == '0') {
             // We need to insert a 1
@@ -376,12 +376,17 @@ int mp_format_float(FPTYPE f, char *buf, size_t buf_size, char fmt, int prec, ch
                 rs[1] = '0';
                 if (e_sign == '-') {
                     e--;
+                    if (e == 0) {
+                        e_sign = '+';
+                    }
                 } else {
-                    e++; 
+                    e++;
                 }
+            } else {
+                // Need at extra digit at the end to make room for the leading '1'
+                s++;
             }
-            s++;
-            char *ss = s; 
+            char *ss = s;
             while (ss > rs) {
                 *ss = ss[-1];
                 ss--;