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Sources/NBKCoreKit/Private/NBKStrictBinaryInteger+Bits.swift
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| //=----------------------------------------------------------------------------= | ||
| // This source file is part of the Numberick open source project. | ||
| // | ||
| // Copyright (c) 2023 Oscar Byström Ericsson | ||
| // Licensed under Apache License, Version 2.0 | ||
| // | ||
| // See http://www.apache.org/licenses/LICENSE-2.0 for license information. | ||
| //=----------------------------------------------------------------------------= | ||
|
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| //*============================================================================* | ||
| // MARK: * NBK x Strict Binary Integer x Bits x Sub Sequence | ||
| //*============================================================================* | ||
|
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| extension NBK.StrictBinaryInteger.SubSequence { | ||
|
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| //=------------------------------------------------------------------------= | ||
| // MARK: Details | ||
| //=------------------------------------------------------------------------= | ||
|
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| /// Returns the leading zero bit count of `base`. | ||
| /// | ||
| /// - Note: The leading zero bit count is zero when `base` is empty. | ||
| /// | ||
| @inlinable public static func leadingZeroBitCount(of base: Base) -> Int { | ||
| var index = base.endIndex | ||
| var element = 0 as Base.Element | ||
|
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| while index > base.startIndex, element.isZero { | ||
| base.formIndex(before: &index) | ||
| element = base[index] | ||
| } | ||
|
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| let product = base.distance(from: index, to: base.endIndex) * Base.Element.bitWidth | ||
| return product - Base.Element.bitWidth + element.leadingZeroBitCount | ||
| } | ||
|
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| /// Returns the trailing zero bit count of `base`. | ||
| /// | ||
| /// - Note: The trailing zero bit count is zero when `base` is empty. | ||
| /// | ||
| @inlinable public static func trailingZeroBitCount(of base: Base) -> Int { | ||
| var index = base.startIndex | ||
| var element = 0 as Base.Element | ||
|
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| while index < base.endIndex, element.isZero { | ||
| element = base[index] | ||
| base.formIndex(after: &index) | ||
| } | ||
|
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| let product = base.distance(from: base.startIndex, to: index) * Base.Element.bitWidth | ||
| return product - Base.Element.bitWidth + element.trailingZeroBitCount | ||
| } | ||
|
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| /// Returns the most significant bit for the two's complement of `base`. | ||
| /// | ||
| /// - Note: The most significant bit does not exist when `base` is empty. | ||
| /// | ||
| @inlinable public static func mostSignificantBit(twosComplementOf base: Base) -> Bool? { | ||
| //=--------------------------------------= | ||
| guard let index = base.firstIndex(where:{ !$0.isZero }) else { return base.isEmpty ? nil : false } | ||
| //=--------------------------------------= | ||
| let lastIndex = base.index(before: base.endIndex) | ||
| return base[lastIndex].twosComplementSubsequence(index == lastIndex).partialValue.mostSignificantBit | ||
| } | ||
|
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| //=------------------------------------------------------------------------= | ||
| // MARK: Details x Nonzero Bit Count | ||
| //=------------------------------------------------------------------------= | ||
|
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| /// Returns the nonzero bit count of `base`. | ||
| /// | ||
| /// - Note: The nonzero bit count is zero when `base` is empty. | ||
| /// | ||
| @inlinable public static func nonzeroBitCount(of base: Base) -> Int { | ||
| base.reduce(0 as Int) { $0 + $1.nonzeroBitCount } | ||
| } | ||
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| /// Returns whether the nonzero bit count of `base` equals `comparand`. | ||
| /// | ||
| /// - Note: The nonzero bit count is zero when `base` is empty. | ||
| /// | ||
| @inlinable public static func nonzeroBitCount(of base: Base, equals comparand: Int) -> Bool { | ||
| var nonzeroBitCount = 0 as Int | ||
| var index: Base.Index = base.startIndex | ||
|
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| while index < base.endIndex, nonzeroBitCount <= comparand { | ||
| nonzeroBitCount += base[index].nonzeroBitCount | ||
| base.formIndex(after: &index) | ||
| } | ||
|
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| return (nonzeroBitCount == comparand) as Bool | ||
| } | ||
|
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| /// Returns the nonzero bit count for the two's complement of `base`. | ||
| /// | ||
| /// - Note: The nonzero bit count is zero when `base` is empty. | ||
| /// | ||
| @inlinable public static func nonzeroBitCount(twosComplementOf base: Base) -> Int { | ||
| //=--------------------------------------= | ||
| guard var index = base.firstIndex(where:{ !$0.isZero }) else { return 0 as Int } | ||
| //=--------------------------------------= | ||
| var nonzeroBitCount: Int = 1 - base[index].trailingZeroBitCount | ||
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| while index < base.endIndex { | ||
| nonzeroBitCount += base[index].onesComplement().nonzeroBitCount | ||
| base.formIndex(after: &index) | ||
| } | ||
|
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| return nonzeroBitCount as Int | ||
| } | ||
| } |
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