private List<Symbol> lookupSymbol(Map<String, List<Symbol>> symbolMap, String prefix,
			String functionName) {

		if (functionName == null || functionName.length() == 0) {
			return null;
		}

		String loolupName = functionName;
		if (prefix != null) {
			loolupName = prefix + functionName;
		}

		List<Symbol> symbols = symbolMap.get(loolupName);
		if (symbols != null) {
			return symbols;
		}

		symbols = symbolMap.get("_" + loolupName);
		return symbols;
	}
Lookup any program symbol with the same name as the function signature.
Also allow for a single '_' in front of the symbol name.

@param symbolMap map of symbol names to all matching symbols
@param prefix  optional prefix on symbol to lookup
@param functionName    function name
@return symbol definition; null if no symbol is found for the given name
Ghidra/Features/Base/src/main/java/ghidra/app/cmd/function/ApplyFunctionDataTypesCmd.java