Introduce new Rational constructor for approximating a Double number.

Author: objecthub

CHANGELOG.md

@@ -1,5 +1,9 @@
 # Changelog
 
+## 2.3.6 (2020-05-01)
+- Fixed serious bug that was leading to a stack overflow if zero was added to a negative `BigInt` number
+- Introduced new `Rational` constructor for approximating a `Double` number as a `Rational` 
+
 ## 2.3.5 (2020-04-05)
 - Port to Swift 5.2
 - Migrated project to Xcode 11.4

NumberKit.xcodeproj/project.pbxproj

@@ -492,7 +492,7 @@
 					"@executable_path/../Frameworks",
 					"@loader_path/Frameworks",
 				);
-				MARKETING_VERSION = 2.3.5;
+				MARKETING_VERSION = 2.3.6;
 				PRODUCT_BUNDLE_IDENTIFIER = net.objecthub.NumberKit;
 				PRODUCT_NAME = "$(TARGET_NAME)";
 				SKIP_INSTALL = YES;
@@ -519,7 +519,7 @@
 					"@executable_path/../Frameworks",
 					"@loader_path/Frameworks",
 				);
-				MARKETING_VERSION = 2.3.5;
+				MARKETING_VERSION = 2.3.6;
 				PRODUCT_BUNDLE_IDENTIFIER = net.objecthub.NumberKit;
 				PRODUCT_NAME = "$(TARGET_NAME)";
 				SKIP_INSTALL = YES;
@@ -584,7 +584,7 @@
 					"@executable_path/Frameworks",
 					"@loader_path/Frameworks",
 				);
-				MARKETING_VERSION = 2.3.5;
+				MARKETING_VERSION = 2.3.6;
 				MTL_ENABLE_DEBUG_INFO = INCLUDE_SOURCE;
 				MTL_FAST_MATH = YES;
 				PRODUCT_BUNDLE_IDENTIFIER = net.objecthub.NumberKit;
@@ -623,7 +623,7 @@
 					"@executable_path/Frameworks",
 					"@loader_path/Frameworks",
 				);
-				MARKETING_VERSION = 2.3.5;
+				MARKETING_VERSION = 2.3.6;
 				MTL_FAST_MATH = YES;
 				PRODUCT_BUNDLE_IDENTIFIER = net.objecthub.NumberKit;
 				PRODUCT_NAME = NumberKit;

Sources/NumberKit/IntegerNumber.swift

@@ -57,10 +57,15 @@ public protocol IntegerNumber: SignedNumeric,
   static func %(lhs: Self, rhs: Self) -> Self
 
   /// Constructs an `IntegerNumber` from an `Int64` value. This constructor might crash if
+  /// the value cannot be converted to this type.
   ///
   /// - Note: This is a hack right now.
   init(_ value: Int64)
 
+  /// Constructs an `IntegerNumber` from a `Double` value. This constructor might crash if
+  /// the value cannot be converted to this type.
+  init(_ value: Double)
+  
   /// Returns the integer as a `Double`.
   var doubleValue: Double { get }
 

Sources/NumberKit/Rational.swift

@@ -141,7 +141,20 @@ public struct Rational<T: IntegerNumber>: RationalNumber, CustomStringConvertibl
   public init(_ value: T) {
     self.init(numerator: value, denominator: T.one)
   }
-
+  
+  /// Creates a rational number by rationalizing a `Double` value.
+  public init(_ value: Double, precision: Double = 1.0e-8) {
+    var x = value
+    var a = Foundation.floor(x)
+    var (h1, k1, h, k) = (T.one, T.zero, T(a), T.one)
+    while x - a > precision * k.doubleValue * k.doubleValue {
+      x = 1.0/(x - a)
+      a = Foundation.floor(x)
+      (h1, k1, h, k) = (h, k, h1 + T(a) * h, k1 + T(a) * k)
+    }
+    self.init(numerator: h, denominator: k)
+  }
+  
   /// Create an instance initialized to `value`.
   public init(integerLiteral value: Int64) {
     self.init(T(value))
@@ -341,7 +354,7 @@ extension Rational: ExpressibleByStringLiteral {
   /// Compute absolute number of `num` and return a tuple consisting of the result and a
   /// boolean indicating whether there was an overflow.
   private static func absWithOverflow(_ num: T) -> (value: T, overflow: Bool) {
-    return num < 0 ? T(0).subtractingReportingOverflow(num) : (num, false)
+    return num < 0 ? T.zero.subtractingReportingOverflow(num) : (num, false)
   }
 
   /// Creates a rational number from a numerator and a denominator.
@@ -355,7 +368,7 @@ extension Rational: ExpressibleByStringLiteral {
     let (adenom, overflow2) = Rational.absWithOverflow(denominator)
     let div = Rational.gcd(anum, adenom)
     let (n, overflow3) = anum.dividedReportingOverflow(by: div)
-    let (numer, overflow4) = negative ? T(0).subtractingReportingOverflow(n) : (n, false)
+    let (numer, overflow4) = negative ? T.zero.subtractingReportingOverflow(n) : (n, false)
     let (denom, overflow5) = adenom.dividedReportingOverflow(by: div)
     return (Rational(numerator: numer, denominator: denom),
             overflow1 || overflow2 || overflow3 || overflow4 || overflow5)

Tests/NumberKitTests/RationalTests.swift

@@ -87,6 +87,17 @@ class RationalTests: XCTestCase {
     XCTAssertEqual(r1, Rational(10 * 49, 3 * 31))
   }
 
+  func testRationalize() {
+    let r1 = Rational<Int>(1.0/3.0)
+    XCTAssertEqual(r1, Rational(1, 3))
+    let r2 = Rational<Int>(1931.0 / 9837491.0, precision: 1.0e-14)
+    XCTAssertEqual(r2, Rational(1931, 9837491))
+    let r3 = Rational<Int>(-17.0/3.0)
+    XCTAssertEqual(r3, -Rational(17, 3))
+    let r4 = Rational<BigInt>(1931.0 / 9837491.0, precision: 1.0e-14)
+    XCTAssertEqual(r4, Rational(BigInt(1931), BigInt(9837491)))
+  }
+  
   static let allTests = [
     ("testConstructors", testConstructors),
     ("testPlus", testPlus),