fix(Decimal128): update toString and fromString methods to correctly handle the case of too many significant digits

Author: kmahar

Diff for: lib/bson/decimal128.js

@@ -325,8 +325,6 @@ Decimal128.fromString = function(string) {
     }
   }
 
-  if (significantDigits > 34) invalidErr(string, 'Too many digits to represent accurately');
-
   // Normalization of exponent
   // Correct exponent based on radix position, and shift significand as needed
   // to represent user input
@@ -392,7 +390,12 @@ Decimal128.fromString = function(string) {
     // If we have seen a radix point, 'string' is 1 longer than we have
     // documented with ndigits_read, so inc the position of the first nonzero
     // digit and the position that digits are read to.
-    if (sawRadix && exponent === EXPONENT_MIN) {
+    if (sawRadix) {
+      firstNonZero = firstNonZero + 1;
+      endOfString = endOfString + 1;
+    }
+    // if negative, we need to increment again to account for - sign at start.
+    if (isNegative) {
       firstNonZero = firstNonZero + 1;
       endOfString = endOfString + 1;
     }
@@ -431,12 +434,8 @@ Decimal128.fromString = function(string) {
               );
             }
           }
-        } else {
-          invalidErr(string, 'overflow');
         }
       }
-    } else {
-      invalidErr(string, 'overflow');
     }
   }
 
@@ -722,9 +721,19 @@ Decimal128.prototype.toString = function() {
   // has trailing zeros.  However, we *cannot* output these trailing zeros,
   // because doing so would change the precision of the value, and would
   // change stored data if the string converted number is round tripped.
-
   if (scientific_exponent >= 34 || scientific_exponent <= -7 || exponent > 0) {
     // Scientific format
+
+    // if there are too many significant digits, we should just be treating numbers
+    // as + or - 0 and using the non-scientific exponent (this is for the "invalid
+    // representation should be treated as 0/-0" spec cases in decimal128-1.json)
+    if (significand_digits > 34) {
+      string.push(0);
+      if (exponent > 0) string.push('E+' + exponent);
+      else if (exponent < 0) string.push('E' + exponent);
+      return string.join('');
+    }
+
     string.push(significand[index++]);
     significand_digits = significand_digits - 1;