ICU-22403 Fix icuexportdata out-of-bounds during decomposition

icu4c/source/tools/icuexportdata/icuexportdata.cpp

@@ -652,7 +652,6 @@ void writeDecompositionData(const char* basename, uint32_t baseSize16, uint32_t
  status.set(U_INTERNAL_PROGRAM_ERROR);
  handleError(status, basename);
  }
- uset_close(halfWidthCheck);
 
  uset_close(iotaSubscript);
  uset_close(halfWidthVoicing);
@@ -710,6 +709,34 @@ UBool permissibleBmpPair(UBool knownToRoundTrip, UChar32 c, UChar32 second) {
  return false;
 }
 
+
+// Find the slice `needle` within `storage` and return its index, failing which,
+// append all elements of `needle` to `storage` and return the index of it at the end.
+template<typename T>
+size_t findOrAppend(std::vector<T>& storage, const UChar32* needle, size_t needleLen) {
+ // Last index where we might find the start of the complete needle.
+ // bounds check is `i + needleLen <= storage.size()` since the inner
+ // loop will range from `i` to `i + needleLen - 1` (the `-1` is why we use `<=`)
+ for (size_t i = 0; i + needleLen <= storage.size(); i++) {
+ for (size_t j = 0;; j++) {
+ if (j == needleLen) {
+ return i; // found a match
+ }
+ if (storage[i + j] != uint32_t(needle[j])) {
+ break;
+ }
+ }
+ }
+ // We didn't find anything. Append, keeping the append index in mind.
+ size_t index = storage.size();
+ for(size_t i = 0; i < needleLen; i++) {
+ storage.push_back(T(needle[i]));
+ }
+
+ return index;
+}
+
+
 // Computes data for canonical decompositions
 void computeDecompositions(const char* basename,
  const USet* backwardCombiningStarters,
@@ -1027,49 +1054,11 @@ void computeDecompositions(const char* basename,
  handleError(status, basename);
  }
  size_t index = 0;
- bool writeToStorage = false;
- // Sadly, C++ lacks break and continue by label, so using goto in the
- // inner loops to break or continue the outer loop.
  if (!supplementary) {
- outer16: for (;;) {
- if (index == storage16.size()) {
- writeToStorage = true;
- break;
- }
- if (storage16[index] == utf32[0]) {
- for (int32_t i = 1; i < len; ++i) {
- if (storage16[index + i] != uint32_t(utf32[i])) {
- ++index;
- // continue outer
- goto outer16;
- }
- }
- // break outer
- goto after;
- }
- ++index;
- }
+ index = findOrAppend(storage16, utf32, len);
  } else {
- outer32: for (;;) {
- if (index == storage32.size()) {
- writeToStorage = true;
- break;
- }
- if (storage32[index] == uint32_t(utf32[0])) {
- for (int32_t i = 1; i < len; ++i) {
- if (storage32[index + i] != uint32_t(utf32[i])) {
- ++index;
- // continue outer
- goto outer32;
- }
- }
- // break outer
- goto after;
- }
- ++index;
- }
+ index = findOrAppend(storage32, utf32, len);
  }
- after:
  if (index > 0xFFF) {
  status.set(U_INTERNAL_PROGRAM_ERROR);
  handleError(status, basename);
@@ -1081,18 +1070,6 @@ void computeDecompositions(const char* basename,
  status.set(U_INTERNAL_PROGRAM_ERROR);
  handleError(status, basename);
  }
- if (writeToStorage) {
- if (!supplementary) {
- for (int32_t i = 0; i < len; ++i) {
- storage16.push_back(uint16_t(utf32[i]));
- }
- } else {
- for (int32_t i = 0; i < len; ++i) {
- storage32.push_back(uint32_t(utf32[i]));
- }
- }
- }
-
  uint32_t nonRoundTripMarker = 0;
  if (!nonNfdOrRoundTrips) {
  nonRoundTripMarker = (NON_ROUND_TRIP_MARKER << 16);