fix float formatting

Lib/snprintf/snprintf.c

@@ -655,6 +655,8 @@ static void fmtfp(char *buffer, size_t *currlen, size_t maxlen,
     int zpadlen = 0;
     int caps = 0;
     int index;
+    int fzeropad = 0;
+    int fzerocnt = 0;
     double intpart;
     double fracpart;
     double temp;
@@ -728,6 +730,13 @@ static void fmtfp(char *buffer, size_t *currlen, size_t maxlen,
 
     /* Convert fractional part */
     if (fracpart) {
+        // leading zeros in the fractional part
+        fzeropad = 0;
+        fzerocnt = max - 1;
+        while (fracpart < POW10(fzerocnt)) {
+            fzeropad++;
+            fzerocnt--;
+        }
         do {
             temp = fracpart;
             my_modf(fracpart * 0.1, &fracpart);
@@ -785,8 +794,19 @@ static void fmtfp(char *buffer, size_t *currlen, size_t maxlen,
     if (max > 0) {
         dopr_outch(buffer, currlen, maxlen, '.');
 
-        while (fplace > 0)
+        if (zpadlen > fzeropad) {
+            zpadlen -= fzeropad;
+        } else {
+            zpadlen = 0;
+        }
+
+        while (fzeropad-- > 0) {
+            dopr_outch(buffer, currlen, maxlen, '0');
+        }
+
+        while (fplace > 0) {
             dopr_outch(buffer, currlen, maxlen, fconvert[--fplace]);
+        }
     }
 
     while (zpadlen > 0) {