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O(1) bit shift operation for UInt128 #1085

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O(1) bit shift operation for UInt128 #1085

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98ea104
Update UInt128.swift
pacowong Jun 10, 2026
972e253
Update UInt128.swift
pacowong Jun 10, 2026
545bc7f
Merge pull request #1 from pacowong/fix/uint128-shift
pacowong Jun 10, 2026
411b98b
Run swiftformat
pacowong Jun 10, 2026
0a3043d
Remove duplicate `let a` declaration in UInt128 right-shift operator
pacowong Jun 10, 2026
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21 changes: 10 additions & 11 deletions Sources/CryptoSwift/UInt128.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -14,9 +14,9 @@
//

#if canImport(FoundationEssentials)
import FoundationEssentials
import FoundationEssentials
#else
import Foundation
import Foundation
#endif

struct UInt128: Equatable, ExpressibleByIntegerLiteral {
Expand All @@ -31,9 +31,9 @@ struct UInt128: Equatable, ExpressibleByIntegerLiteral {
init(_ raw: Array<UInt8>) {
precondition(raw.count >= 16, "UInt128 requires at least 16 bytes")
let a = UInt64(raw[0]) << 56 | UInt64(raw[1]) << 48 | UInt64(raw[2]) << 40 | UInt64(raw[3]) << 32 |
UInt64(raw[4]) << 24 | UInt64(raw[5]) << 16 | UInt64(raw[6]) << 8 | UInt64(raw[7])
UInt64(raw[4]) << 24 | UInt64(raw[5]) << 16 | UInt64(raw[6]) << 8 | UInt64(raw[7])
let b = UInt64(raw[8]) << 56 | UInt64(raw[9]) << 48 | UInt64(raw[10]) << 40 | UInt64(raw[11]) << 32 |
UInt64(raw[12]) << 24 | UInt64(raw[13]) << 16 | UInt64(raw[14]) << 8 | UInt64(raw[15])
UInt64(raw[12]) << 24 | UInt64(raw[13]) << 16 | UInt64(raw[14]) << 8 | UInt64(raw[15])
Comment on lines 17 to +36

@pacowong pacowong Jun 10, 2026

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modified by swiftformat

self.init((a, b))
}

Expand Down Expand Up @@ -76,13 +76,12 @@ struct UInt128: Equatable, ExpressibleByIntegerLiteral {
}

static func >> (value: UInt128, by: Int) -> UInt128 {
var result = value
for _ in 0..<by {
let a = result.i.a >> 1
let b = result.i.b >> 1 + ((result.i.a & 1) << 63)
result = UInt128((a, b))
}
return result
guard by > 0 else { return value }
guard by < 128 else { return UInt128(a: 0, b: 0) }
guard by < 64 else { return UInt128(a: 0, b: value.i.a >> (by - 64)) }
let a = value.i.a >> by
let b = (value.i.b >> by) | (value.i.a << (64 - by))
return UInt128(a: a, b: b)
}

// Equatable.
Expand Down