Speed up hex encode/decode with lookup tables

Data.hexEncodedString() built each byte via String(format: "%02x", _), paying Foundation format-string parsing per byte on the hot BLE receive path (PeerID(hexData:) is called several times per received packet). Replace it with an ASCII lookup table writing into a preallocated buffer; output is byte-for-byte identical (lowercase hex). Data(hexString:) similarly allocated a two-character substring and went through integer radix parsing per byte; replace with direct nibble lookups over the UTF-8 bytes. Semantics are unchanged except that sign-prefixed pairs like "+f", which the old radix parser incorrectly accepted, are now rejected. Add round-trip, known-vector, and invalid-input tests to BitFoundationTests. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
2026-07-25 07:05:20 +00:00 · 2026-07-01 23:26:38 +02:00
parent f688e529f6
commit 3f6dc7dd36
2 changed files with 124 additions and 14 deletions
@@ -0,0 +1,78 @@
+//
+// DataHexTests.swift
+// bitchatTests
+//
+// This is free and unencumbered software released into the public domain.
+// For more information, see <https://unlicense.org>
+//
+
+import Testing
+import Foundation
+@testable import BitFoundation
+
+struct DataHexTests {
+
+    // MARK: - Encoding
+
+    @Test func encode_knownVectors() {
+        #expect(Data().hexEncodedString() == "")
+        #expect(Data([0x00]).hexEncodedString() == "00")
+        #expect(Data([0x0f]).hexEncodedString() == "0f")
+        #expect(Data([0xf0]).hexEncodedString() == "f0")
+        #expect(Data([0xff]).hexEncodedString() == "ff")
+        #expect(Data([0xde, 0xad, 0xbe, 0xef]).hexEncodedString() == "deadbeef")
+        #expect(Data([0x01, 0x23, 0x45, 0x67, 0x89, 0xab, 0xcd, 0xef]).hexEncodedString() == "0123456789abcdef")
+    }
+
+    @Test func encode_allByteValues_matchesFormatReference() {
+        let all = Data((0...255).map { UInt8($0) })
+        let reference = (0...255).map { String(format: "%02x", $0) }.joined()
+        #expect(all.hexEncodedString() == reference)
+    }
+
+    @Test func encode_worksOnDataSlices() {
+        let data = Data([0xaa, 0xde, 0xad, 0xbe, 0xef, 0xbb])
+        let slice = data.dropFirst().dropLast()
+        #expect(slice.hexEncodedString() == "deadbeef")
+    }
+
+    // MARK: - Decoding
+
+    @Test func decode_knownVectors() {
+        #expect(Data(hexString: "deadbeef") == Data([0xde, 0xad, 0xbe, 0xef]))
+        #expect(Data(hexString: "DEADBEEF") == Data([0xde, 0xad, 0xbe, 0xef]))
+        #expect(Data(hexString: "DeAdBeEf") == Data([0xde, 0xad, 0xbe, 0xef]))
+        #expect(Data(hexString: "00") == Data([0x00]))
+        #expect(Data(hexString: "0123456789abcdef") == Data([0x01, 0x23, 0x45, 0x67, 0x89, 0xab, 0xcd, 0xef]))
+    }
+
+    @Test func decode_handlesPrefixAndWhitespace() {
+        #expect(Data(hexString: "0xdeadbeef") == Data([0xde, 0xad, 0xbe, 0xef]))
+        #expect(Data(hexString: "0XDEADBEEF") == Data([0xde, 0xad, 0xbe, 0xef]))
+        #expect(Data(hexString: "  deadbeef\n") == Data([0xde, 0xad, 0xbe, 0xef]))
+        #expect(Data(hexString: "") == Data())
+        #expect(Data(hexString: "0x") == Data())
+    }
+
+    @Test func decode_rejectsInvalidInput() {
+        #expect(Data(hexString: "abc") == nil)        // odd length
+        #expect(Data(hexString: "zz") == nil)         // non-hex characters
+        #expect(Data(hexString: "0xg1") == nil)       // non-hex after prefix
+        #expect(Data(hexString: "+f") == nil)         // sign characters are not hex
+        #expect(Data(hexString: "-0") == nil)
+        #expect(Data(hexString: "a\u{00e9}") == nil)  // non-ASCII
+        #expect(Data(hexString: "de ad") == nil)      // interior whitespace
+    }
+
+    // MARK: - Round trip
+
+    @Test func roundTrip_randomLengths() {
+        for length in [0, 1, 2, 3, 8, 16, 31, 32, 33, 64, 255, 1024] {
+            let data = Data((0..<length).map { _ in UInt8.random(in: .min ... .max) })
+            let hex = data.hexEncodedString()
+            #expect(hex.count == length * 2)
+            #expect(Data(hexString: hex) == data)
+            #expect(Data(hexString: hex.uppercased()) == data)
+        }
+    }
+}