The problem is not finding where the constants are defined, it's about finding what the code does based on a hardware datasheet, the constants could be in a fil

The problem is not finding where the constants are defined, it's about finding what the code does based on a hardware datasheet, the constants could be in a file, or could be scattered throughout, it doesn't matter at all. You can also use the magic of base 16 to search for lexical subsets of a value to find where code uses things with the same mask, which are probably related. Extremely effective in reverse engineering a hardware device.