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fix: slightly better fuzzy scanning #115

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fix: slightly better fuzzy scanning #115

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0df6e46
fix: slightly better fuzzy scanning, succeeds if instructions are mis…
MewtR Oct 10, 2022
b528091
Merge branch 'dev' into betterfuzzyscanning
oSumAtrIX Feb 10, 2023
b1b0762
Merge branch 'dev' into betterfuzzyscanning
oSumAtrIX Mar 2, 2023
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21 changes: 18 additions & 3 deletions src/main/kotlin/app/revanced/patcher/fingerprint/method/impl/MethodFingerprint.kt
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Original file line number Diff line number Diff line change
Expand Up @@ -158,18 +158,33 @@ abstract class MethodFingerprint(
for (index in 0 until instructionLength) {
var patternIndex = 0
var threshold = fingerprintFuzzyPatternScanThreshold
var offset = 0;

while (index + patternIndex < instructionLength) {
scan@ while (index + patternIndex < instructionLength) {
val originalOpcode = instructions.elementAt(index + patternIndex).opcode
val patternOpcode = pattern.elementAt(patternIndex)
val patternOpcode = pattern.elementAt(patternIndex + offset)

if (patternOpcode != null && patternOpcode.ordinal != originalOpcode.ordinal) {
// reaching maximum threshold (0) means,
// the pattern does not match to the current instructions
if (threshold-- == 0) break

// look ahead
for (depth in 1 until threshold + 2) {
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Is threshold + 2 arbitrary?

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Kind of, I wanted to make it so that at a minimum at least the next instruction is considered. If threshold is 0 at that point, you'll only enter that loop once since you start at 1 and would go 'until' 2 (exclusive).

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@oSumAtrIX

val lookAheadIndex = patternIndex + offset + depth
if (lookAheadIndex < patternLength && index + lookAheadIndex < instructionLength)
{
val nextPatternOpcode = pattern.elementAt(lookAheadIndex)
if (nextPatternOpcode != null && nextPatternOpcode.ordinal == originalOpcode.ordinal)
{
offset+=depth;
continue@scan;
}
}
}
}

if (patternIndex < patternLength - 1) {
if (patternIndex + offset < patternLength - 1) {
// if the entire pattern has not been scanned yet
// continue the scan
patternIndex++
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