O(1) bit shift operation for UInt128#1085
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Signed-off-by: pacowong <paco@goodnotesapp.com>
Signed-off-by: pacowong <paco@goodnotesapp.com>
Update UInt128.swift
Co-Authored-By: Claude Sonnet 4.6 (1M context) <noreply@anthropic.com>
pacowong
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Jun 10, 2026
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| @@ -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]) | |||
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Fixes #
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Changes proposed in this pull request:
>>right-shift operator onUInt128with an O(1) direct bit-manipulation implementation. The previous code shifted one bit at a time in a loop (for _ in 0..<by), degrading linearly with the shift amount. The new implementation handles all cases in constant time: early exits for shift ≤ 0, shift ≥ 128, and shift ≥ 64, with a single-expression bit combine for the general case ((value.i.b >> by) | (value.i.a << (64 - by))).