From 2d3c2eec5506695b9cae5f88a56ea95529bfbea6 Mon Sep 17 00:00:00 2001
From: Simon Evans <si@si.org>
Date: Tue, 29 Dec 2020 01:12:35 +0000
Subject: [PATCH] Decimal: init?(string:) and scanDecimal() should return nil
 on error.

- If the exponent is too large for Int8 then return nil instead of NaN.

- This matches Darwin's behaviour.
---
 Sources/Foundation/Decimal.swift         |  8 +++---
 Tests/Foundation/Tests/TestDecimal.swift | 31 ++++++++++++++++++++++--
 2 files changed, 33 insertions(+), 6 deletions(-)

diff --git a/Sources/Foundation/Decimal.swift b/Sources/Foundation/Decimal.swift
index 6d4d50fad4..2960f0fcb1 100644
--- a/Sources/Foundation/Decimal.swift
+++ b/Sources/Foundation/Decimal.swift
@@ -2295,7 +2295,7 @@ extension Scanner {
                     repeat {
                         buf.advance()
                     } while decimalValue(buf.currentCharacter) != nil
-                    return Decimal.nan
+                    return nil
                 }
                 result._exponent += 1
             }
@@ -2315,7 +2315,7 @@ extension Scanner {
                         repeat {
                             buf.advance()
                         } while decimalValue(buf.currentCharacter) != nil
-                        return Decimal.nan
+                        return nil
                     }
                     result._exponent -= 1
                 }
@@ -2339,7 +2339,7 @@ extension Scanner {
             while let numeral = decimalValue(buf.currentCharacter) {
                 exponent = 10 * exponent + Int32(numeral)
                 guard exponent <= 2*Int32(Int8.max) else {
-                    return Decimal.nan
+                    return nil
                 }
 
                 buf.advance()
@@ -2350,7 +2350,7 @@ extension Scanner {
             }
             exponent += result._exponent
             guard exponent >= Int32(Int8.min) && exponent <= Int32(Int8.max) else {
-                return Decimal.nan
+                return nil
             }
             result._exponent = exponent
         }
diff --git a/Tests/Foundation/Tests/TestDecimal.swift b/Tests/Foundation/Tests/TestDecimal.swift
index 590d7a99db..8bef77b21e 100644
--- a/Tests/Foundation/Tests/TestDecimal.swift
+++ b/Tests/Foundation/Tests/TestDecimal.swift
@@ -749,7 +749,7 @@ class TestDecimal: XCTestCase {
         }
     }
 
-    func test_ScanDecimal() {
+    func test_ScanDecimal() throws {
         let testCases = [
             // expected, value
             ( 123.456e78, "123.456e78" ),
@@ -764,7 +764,7 @@ class TestDecimal: XCTestCase {
         ]
         for testCase in testCases {
             let (expected, string) = testCase
-            let decimal = Decimal(string:string)!
+            let decimal = try XCTUnwrap(Decimal(string:string))
             let aboutOne = Decimal(expected) / decimal
             let approximatelyRight = aboutOne >= Decimal(0.99999) && aboutOne <= Decimal(1.00001)
             XCTAssertTrue(approximatelyRight, "\(expected) ~= \(decimal) : \(aboutOne) \(aboutOne >= Decimal(0.99999)) \(aboutOne <= Decimal(1.00001))" )
@@ -779,6 +779,33 @@ class TestDecimal: XCTestCase {
             return
         }
         XCTAssertEqual(answer,num,"\(ones) / 9 = \(answer) \(num)")
+
+        // Exponent overflow, returns nil
+        XCTAssertNil(Decimal(string: "1e200"))
+        XCTAssertNil(Decimal(string: "1e-200"))
+        XCTAssertNil(Decimal(string: "1e300"))
+        XCTAssertNil(Decimal(string: "1" + String(repeating: "0", count: 170)))
+        XCTAssertNil(Decimal(string: "0." + String(repeating: "0", count: 170) + "1"))
+        XCTAssertNil(Decimal(string: "0e200"))
+
+        // Parsing zero in different forms
+        let zero1 = try XCTUnwrap(Decimal(string: "000.000e123"))
+        XCTAssertTrue(zero1.isZero)
+        XCTAssertEqual(zero1._isNegative, 0)
+        XCTAssertEqual(zero1._length, 0)
+        XCTAssertEqual(zero1.description, "0")
+
+        let zero2 = try XCTUnwrap(Decimal(string: "+000.000e-123"))
+        XCTAssertTrue(zero2.isZero)
+        XCTAssertEqual(zero2._isNegative, 0)
+        XCTAssertEqual(zero2._length, 0)
+        XCTAssertEqual(zero2.description, "0")
+
+        let zero3 = try XCTUnwrap(Decimal(string: "-0.0e1"))
+        XCTAssertTrue(zero3.isZero)
+        XCTAssertEqual(zero3._isNegative, 0)
+        XCTAssertEqual(zero3._length, 0)
+        XCTAssertEqual(zero3.description, "0")
     }
 
     func test_SimpleMultiplication() {