toString: Fix bug in emitting exponential notation

spec.emu

@@ -291,52 +291,37 @@ location: https://github.com/tc39/proposal-amount/
       <emu-clause id="sec-amount-rendermvwithfractiondigits" type="abstract operation">
         <h1>RenderAmountValueWithFractionDigits (
           _v_: an Intl mathematical value,
-          _numDigits_: an integer,
-          optional _roundingMode_: a rounding mode
+          _fractionDigits_: an integer
         ): a String
         </h1>
         <dl class="header">
           <dt>description</dt>
-          <dd>It renders the given Intl mathematical value with a given number of fractional digits, rounding, if necessary, using the given rounding mode, which, if missing, is *"halfEven"*.</dd>
+          <dd>It renders the given Intl mathematical value with a given number of fractional digits</dd>
         </dl>
         <emu-alg>
           1. If _v_ is ~not-a-number~, return *"NaN"*.
           1. If _v_ is ~negative-infinity~, return *"-Infinity"*.
           1. If _v_ is ~positive-infinity~, return *"Infinity"*.
           1. If _v_ is ~minus-zero~, then
-            1. If _numDigits_ < 0, then
-              1. Let _exp_ be the unique string representation of -_numDigits_ in base 10 without duplicate leading zeros.
-              1. Return the string-concatenation of *"0"*, *"e"*, and _exp_.
-            1. Otherwise:
-              1. Let _trailingZeroes_ be *"0"* repeated _numDigits_ times.
-              1. Let _z_ be *"-0"*.
-              1. If _numDigits_ = 0, return _z_.
-              1. Otherwise, return the string-concatenation of _z_, *"."* and _trailingZeroes_.
-          1. If _roundingMode_ is *undefined*, set _roundingMode_ to *"halfEven"*.
+            1. Let _s_ be RenderAmountValueWithFractionDigits(0, _fractionDigits_:).
+            1. Return the string-concatenation of *"-"* and _s_.
           1. If _v_ < 0, let _prefix_ be *"-"*, else let _prefix_ be "".
-          1. If _v_ < 0, then
-            1. Set _v_ to -_v_.
-            1. Set _roundingMode_ to ReverseRoundingMode(_roundingMode_).
-          1. Let _rounded_ be ApplyRoundingModeToPositive(_v_ × 10<sup>_numDigits_</sup>, _roundingMode_).
-          1. Let _e_ be the smallest non-negative integer such that _rounded_ × 10<sup>-_numDigits_</sup> is an integer.
-          1. Let _s_ be the unique decimal string representation of _rounded_ without duplicate leading zeroes.
-          1. If _numDigits_ > _e_, then
-            1. If _v_ is an integer, return the string-concatenation of _prefix, _s_, *"."*, and *"0"* repeated _numDigits_ times.
-            1. Otherwise, return the string-concatenation of _prefix_, _s_ and *"0"* repeated _numDigits_ - _e_ times.
-          1. If 0 < _numDigits_, then
-            1. Return the string-concatenation of _prefix, _s_ and *"0"* repeated _e_ - _numDigits_ times.
+          1. If _v_ < 0, set _v_ to -_v_.
+          1. Let _e_ be the smallest non-negative integer such that _v_ × 10<sup>-_e_</sup> is an integer.
+          1. If _v_ = 0, let _s_ be *"0"*, else let _s_ be the unique decimal string representation of _v_ that either starts with "0." or does not start with "0".
+          1. If _e_ < _fractionDigits_, then
+            1. If _v_ is an integer, return the string-concatenation of _prefix_, _s_, *"."*, and *"0"* repeated _fractionDigits_ times.
+            1. Otherwise, return the string-concatenation of _prefix_, _s_ and *"0"* repeated _fractionDigits_ - _e_ times.
+          1. Else if 0 ≤ _fractionDigits_, then
+            1. Return the string-concatenation of _prefix, _s_ and *"0"* repeated _e_ - _fractionDigits_ times.
           1. Otherwise:
-            1. Assert: _rounded_ is an integer.
             1. Let _firstDigit_ be the substring of _s_ from 0 to 1.
-            1. Let _p_ be the unique integer such that 1 ≤ _rounded_ × 10<sup>_p_</sup> < 10.
-            1. Let _n_ be _p_ + _numDigits_.
-            1. Assert: _n_ ≥ 0.
-            1. Let _exp_ be the unique string representation of _n_ in base-10 without duplicate leading zeros.
-            1. If _n_ = 0, then
-              1. Return the string-concatenation of _s_, *"e"*, and _exp_.
-            1. Otherwise:
-              1. Let _remainingDigits_ be the substring of _s_ from 1 to _n_.
-              1. Return the string-concatenation of _firstDigit_, *"."*, _remainingDigits_, *"e"*, and _exp_.
+            1. If _v_ = 0, let _p_ be 0, else let _p_ be the unique integer such that 1 ≤ _v_ × 10<sup>_p_</sup> < 10.
+            1. Let _n_ be _p_ + _fractionDigits_.
+            1. Assert: _n_ < 0.
+            1. Let _exp_ be the unique string representation of -_n_ in base-10 without duplicate leading zeros.
+            1. Let _remainingDigits_ be the substring of _s_ from 1 to _n_.
+            1. Return the string-concatenation of _firstDigit_, *"."*, _remainingDigits_, *"e"*, and _exp_.
         </emu-alg>
       </emu-clause>