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//===----------------------------------------------------------------------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2022 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
//
//===----------------------------------------------------------------------===//
/// An immutable arbitrary-precision signed integer.
///
/// `StaticBigInt` is primarily intended to be used as the associated type of an
/// `ExpressibleByIntegerLiteral` conformance.
///
/// extension UInt256: ExpressibleByIntegerLiteral {
/// public init(integerLiteral value: StaticBigInt) {
/// precondition(
/// value.signum() >= 0 && value.bitWidth <= 1 + Self.bitWidth,
/// "integer overflow: '\(value)' as '\(Self.self)'"
/// )
/// self.words = Words()
/// for wordIndex in 0..<Words.count {
/// self.words[wordIndex] = value[wordIndex]
/// }
/// }
/// }
@available(SwiftStdlib 5.8, *)
@frozen
public struct StaticBigInt:
_ExpressibleByBuiltinIntegerLiteral,
ExpressibleByIntegerLiteral,
Sendable
{
@available(SwiftStdlib 5.8, *)
@usableFromInline
internal let _value: Builtin.IntLiteral
@available(SwiftStdlib 5.8, *)
@inlinable
public init(_builtinIntegerLiteral value: Builtin.IntLiteral) {
_value = value
}
}
//===----------------------------------------------------------------------===//
// MARK: - Binary Representation
//===----------------------------------------------------------------------===//
@available(SwiftStdlib 5.8, *)
extension StaticBigInt {
/// Indicates the value's sign.
///
/// - Returns: `-1` if the value is less than zero, `0` if it is equal to
/// zero, or `+1` if it is greater than zero.
@available(SwiftStdlib 5.8, *)
@inlinable
public func signum() -> Int {
_isNegative ? -1 : (bitWidth == 1) ? 0 : +1
}
@available(SwiftStdlib 5.8, *)
@inlinable
internal var _isNegative: Bool {
#if compiler(>=5.8) && $BuiltinIntLiteralAccessors
Bool(Builtin.isNegative_IntLiteral(_value))
#else
fatalError("Swift compiler is incompatible with this SDK version")
#endif
}
/// Returns the minimal number of bits in this value's binary representation,
/// including the sign bit, and excluding the sign extension.
///
/// The following examples show the least significant byte of each value's
/// binary representation, separated (by an underscore) into excluded and
/// included bits. Negative values are in two's complement.
///
/// * `-4` (`0b11111_100`) is 3 bits.
/// * `-3` (`0b11111_101`) is 3 bits.
/// * `-2` (`0b111111_10`) is 2 bits.
/// * `-1` (`0b1111111_1`) is 1 bit.
/// * `+0` (`0b0000000_0`) is 1 bit.
/// * `+1` (`0b000000_01`) is 2 bits.
/// * `+2` (`0b00000_010`) is 3 bits.
/// * `+3` (`0b00000_011`) is 3 bits.
@available(SwiftStdlib 5.8, *)
@inlinable
public var bitWidth: Int {
#if compiler(>=5.8) && $BuiltinIntLiteralAccessors
Int(Builtin.bitWidth_IntLiteral(_value))
#else
fatalError("Swift compiler is incompatible with this SDK version")
#endif
}
/// Returns a 32-bit or 64-bit word of this value's binary representation.
///
/// The words are ordered from least significant to most significant, with
/// an infinite sign extension. Negative values are in two's complement.
///
/// let negative: StaticBigInt = -0x0011223344556677_8899AABBCCDDEEFF
/// negative.signum() //-> -1
/// negative.bitWidth //-> 118
/// negative[0] //-> 0x7766554433221101
/// negative[1] //-> 0xFFEEDDCCBBAA9988
/// negative[2] //-> 0xFFFFFFFFFFFFFFFF
///
/// let positive: StaticBigInt = 0x0011223344556677_8899AABBCCDDEEFF
/// positive.signum() //-> +1
/// positive.bitWidth //-> 118
/// positive[0] //-> 0x8899AABBCCDDEEFF
/// positive[1] //-> 0x0011223344556677
/// positive[2] //-> 0x0000000000000000
///
/// - Parameter wordIndex: A nonnegative zero-based offset.
@available(SwiftStdlib 5.8, *)
@inlinable
public subscript(_ wordIndex: Int) -> UInt {
_precondition(wordIndex >= 0, "Negative word index")
let bitIndex = wordIndex.multipliedReportingOverflow(by: UInt.bitWidth)
guard !bitIndex.overflow, bitIndex.partialValue < bitWidth else {
return _isNegative ? ~0 : 0
}
#if compiler(>=5.8) && $BuiltinIntLiteralAccessors
return UInt(
Builtin.wordAtIndex_IntLiteral(_value, wordIndex._builtinWordValue)
)
#else
fatalError("Swift compiler is incompatible with this SDK version")
#endif
}
}
//===----------------------------------------------------------------------===//
// MARK: - Textual Representation
//===----------------------------------------------------------------------===//
@available(SwiftStdlib 5.8, *)
extension StaticBigInt: CustomDebugStringConvertible {
@available(SwiftStdlib 5.8, *)
public var debugDescription: String {
let isNegative = _isNegative
let indicator = isNegative ? "-0x" : "+0x"
// Equivalent to `ceil(bitWidthExcludingSignBit / fourBitsPerHexDigit)`.
// Underestimated for `-(16 ** y)` values (e.g. "-0x1", "-0x10", "-0x100").
let capacity = indicator.utf8.count + (((bitWidth - 1) + 3) / 4)
var result = String(unsafeUninitializedCapacity: capacity) { utf8 in
// Pre-initialize with zeros, ignoring extra capacity.
var utf8 = utf8.prefix(capacity)
utf8.initialize(repeating: UInt8(ascii: "0"))
// Use a 32-bit element type, to generate small hexadecimal strings.
typealias Element = UInt32
let hexDigitsPerElement = Element.bitWidth / 4
_internalInvariant(hexDigitsPerElement <= _SmallString.capacity)
_internalInvariant(UInt.bitWidth.isMultiple(of: Element.bitWidth))
// Lazily compute the magnitude, starting with the least significant bits.
var overflow = isNegative
for bitIndex in stride(from: 0, to: bitWidth, by: Element.bitWidth) {
let wordIndex = bitIndex >> UInt.bitWidth.trailingZeroBitCount
var element = Element(_truncatingBits: self[wordIndex] &>> bitIndex)
if isNegative {
element = ~element
if overflow {
(element, overflow) = element.addingReportingOverflow(1)
}
}
// Overwrite trailing zeros with hexadecimal digits.
let hexDigits = String(element, radix: 16, uppercase: true).utf8
_ = utf8.suffix(hexDigits.count).update(fromContentsOf: hexDigits)
utf8 = utf8.dropLast(hexDigitsPerElement)
}
return capacity
}
// Overwrite leading zeros with the "±0x" indicator.
if let upToIndex = result.firstIndex(where: { $0 != "0" }) {
result.replaceSubrange(..<upToIndex, with: indicator)
} else {
result = "+0x0"
}
return result
}
}
#if SWIFT_ENABLE_REFLECTION
@available(SwiftStdlib 5.8, *)
extension StaticBigInt: CustomReflectable {
@available(SwiftStdlib 5.8, *)
public var customMirror: Mirror {
Mirror(self, unlabeledChildren: EmptyCollection<Void>())
}
}
#endif
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