[nfc][lldb] Move FastSearch from CommandObjectMemoryFind to Process (#93688)

Moving CommandObjectMemoryFind::FastSearch() to Process::FindInMemory(). Plan to expose FindInMemory as public API in SBProcess.

lldb/source/Target/Process.cpp

@@ -112,6 +112,33 @@ public:
   }
 };
 
+class ProcessMemoryIterator {
+public:
+  ProcessMemoryIterator(Process &process, lldb::addr_t base)
+      : m_process(process), m_base_addr(base) {}
+
+  bool IsValid() { return m_is_valid; }
+
+  uint8_t operator[](lldb::addr_t offset) {
+    if (!IsValid())
+      return 0;
+
+    uint8_t retval = 0;
+    Status error;
+    if (0 == m_process.ReadMemory(m_base_addr + offset, &retval, 1, error)) {
+      m_is_valid = false;
+      return 0;
+    }
+
+    return retval;
+  }
+
+private:
+  Process &m_process;
+  const lldb::addr_t m_base_addr;
+  bool m_is_valid = true;
+};
+
 static constexpr OptionEnumValueElement g_follow_fork_mode_values[] = {
     {
         eFollowParent,
@@ -3191,6 +3218,33 @@ Status Process::Halt(bool clear_thread_plans, bool use_run_lock) {
   return Status();
 }
 
+lldb::addr_t Process::FindInMemory(lldb::addr_t low, lldb::addr_t high,
+                                   const uint8_t *buf, size_t size) {
+  const size_t region_size = high - low;
+
+  if (region_size < size)
+    return LLDB_INVALID_ADDRESS;
+
+  std::vector<size_t> bad_char_heuristic(256, size);
+  ProcessMemoryIterator iterator(*this, low);
+
+  for (size_t idx = 0; idx < size - 1; idx++) {
+    decltype(bad_char_heuristic)::size_type bcu_idx = buf[idx];
+    bad_char_heuristic[bcu_idx] = size - idx - 1;
+  }
+  for (size_t s = 0; s <= (region_size - size);) {
+    int64_t j = size - 1;
+    while (j >= 0 && buf[j] == iterator[s + j])
+      j--;
+    if (j < 0)
+      return low + s;
+    else
+      s += bad_char_heuristic[iterator[s + size - 1]];
+  }
+
+  return LLDB_INVALID_ADDRESS;
+}
+
 Status Process::StopForDestroyOrDetach(lldb::EventSP &exit_event_sp) {
   Status error;