[stdlib] Replace Integer Parsing Code

Author: Dave Abrahams

stdlib/public/core/CMakeLists.txt

@@ -73,7 +73,7 @@ set(SWIFTLIB_ESSENTIAL
   Index.swift
   Indices.swift.gyb
   InputStream.swift
-  IntegerParsing.swift.gyb
+  IntegerParsing.swift
   Integers.swift.gyb
   Join.swift
   KeyPath.swift

stdlib/public/core/IntegerParsing.swift

@@ -0,0 +1,143 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2017 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+@inline(__always)
+internal func _asciiDigit<CodeUnit : UnsignedInteger, Result : BinaryInteger>(
+  codeUnit u_: CodeUnit, radix: Result
+) -> Result? {
+  let digit = _ascii16("0")..._ascii16("9")
+  let lower = _ascii16("a")..._ascii16("z")
+  let upper = _ascii16("A")..._ascii16("Z")
+
+  let u = UInt16(extendingOrTruncating: u_)
+  let d: UInt16
+  if _fastPath(digit ~= u) { d = u &- digit.lowerBound }
+  else if _fastPath(upper ~= u) { d = u &- upper.lowerBound &+ 10 }
+  else if _fastPath(lower ~= u) { d = u &- lower.lowerBound &+ 10 }
+  else { return nil }
+  guard _fastPath(d < radix) else { return nil }
+  return Result(extendingOrTruncating: d)
+}
+
+@inline(__always)
+internal func _parseUnsignedASCII<
+  Rest : IteratorProtocol, Result: FixedWidthInteger
+>(
+  first: Rest.Element, rest: inout Rest, radix: Result, positive: Bool
+) -> Result?
+where Rest.Element : UnsignedInteger {
+  let r0 = _asciiDigit(codeUnit: first, radix: radix)
+  guard _fastPath(r0 != nil), var result = r0 else { return nil }
+  if !positive {
+    let (result0, overflow0)
+      = (0 as Result).subtractingReportingOverflow(result)
+    guard _fastPath(overflow0 == .none) else { return nil }
+    result = result0
+  }
+  
+  while let u = rest.next() {
+    let d0 = _asciiDigit(codeUnit: u, radix: radix)
+    guard _fastPath(d0 != nil), let d = d0 else { return nil }
+    let (result1, overflow1) = result.multipliedReportingOverflow(by: radix)
+    let (result2, overflow2) = positive
+      ? result1.addingReportingOverflow(d)
+      : result1.subtractingReportingOverflow(d)
+    guard _fastPath(overflow1 == .none && overflow2 == .none)
+    else { return nil }
+    result = result2
+  }
+  return result
+}
+
+@inline(__always)
+internal func _parseASCII<
+  CodeUnits : IteratorProtocol, Result: FixedWidthInteger
+>(
+  codeUnits: inout CodeUnits, radix: Result
+) -> Result?
+where CodeUnits.Element : UnsignedInteger {
+  let c0_ = codeUnits.next()
+  guard _fastPath(c0_ != nil), let c0 = c0_ else { return nil }
+  if _fastPath(c0 != _ascii16("+") && c0 != _ascii16("-")) {
+    return _parseUnsignedASCII(
+      first: c0, rest: &codeUnits, radix: radix, positive: true)
+  }
+  let c1_ = codeUnits.next()
+  guard _fastPath(c1_ != nil), let c1 = c1_ else { return nil }
+  if _fastPath(c0 == _ascii16("-")) {
+    return _parseUnsignedASCII(
+      first: c1, rest: &codeUnits, radix: radix, positive: false)
+  }
+  else {
+    return _parseUnsignedASCII(
+      first: c1, rest: &codeUnits, radix: radix, positive: true)
+  }
+}
+
+extension FixedWidthInteger {
+  /// Creates a new integer value from the given string and radix.
+  ///
+  /// The string passed as `text` may begin with a plus or minus sign character
+  /// (`+` or `-`), followed by one or more numeric digits (`0-9`) or letters
+  /// (`a-z` or `A-Z`). The string is case insensitive.
+  ///
+  ///     let x = Int("123")
+  ///     // x == 123
+  ///
+  ///     let y = Int("-123", radix: 8)
+  ///     // y == -83
+  ///     let y = Int("+123", radix: 8)
+  ///     // y == +83
+  ///
+  ///     let z = Int("07b", radix: 16)
+  ///     // z == 123
+  ///
+  /// If `text` is in an invalid format or contains characters that are out of
+  /// range for the given `radix`, or if the value it denotes in the given
+  /// `radix` is not representable, the result is `nil`. For example, the
+  /// following conversions result in `nil`:
+  ///
+  ///     Int(" 100")                       // Includes whitespace
+  ///     Int("21-50")                      // Invalid format
+  ///     Int("ff6600")                     // Characters out of bounds
+  ///     Int("zzzzzzzzzzzzz", radix: 36)   // Out of range
+  ///
+  /// - Parameters:
+  ///   - text: The ASCII representation of a number in the radix passed as
+  ///     `radix`.
+  ///   - radix: The radix, or base, to use for converting `text` to an integer
+  ///     value. `radix` must be in the range `2...36`. The default is 10.
+  public init?/*<S : StringProtocol>*/(_ text: String, radix: Int = 10) {
+    _precondition(2...36 ~= radix, "Radix not in range 2...36")
+    let r = Self(radix)
+    let s = text// ._ephemeralString
+    defer { _fixLifetime(s) }
+    
+    let c = s._core
+    let result: Self?
+    if _slowPath(c._baseAddress == nil) {
+      var i = s.utf16.makeIterator()
+      result = _parseASCII(codeUnits: &i, radix: r)
+    }
+    else if _fastPath(c.elementWidth == 1), let a = c.asciiBuffer {
+      var i = a.makeIterator()
+      result = _parseASCII(codeUnits: &i, radix: r)
+    }
+    else {
+      let b = UnsafeBufferPointer(start: c.startUTF16, count: c.count)
+      var i = b.makeIterator()
+      result = _parseASCII(codeUnits: &i, radix: r)
+    }
+    guard _fastPath(result != nil) else { return nil }
+    self = result!
+  }
+}