best way to check for modification of self

I am looking for C src or algorithms that would be useful for a program to check its own integrity and make sure it hasnt been modified. Looking at the filesize of the file would not help, since I want to make sure no one has modified just some text, etc. I would like the algorithm or code to be rather quick in doing the check in the initialization of the program. Would finding the src to CRC or sum and adding that into the program be the best solution? Has anyone else dealt with this? -- Christopher Klaus klaus@mail.lds.loral.com cklaus@hotsun.nersc.gov