I was just reading the OpenCL 1.2 specification and I noticed that between 1.1 and 1.2 the cl_khr_fp64 went from being an extension to an "optional core feature". From appendix F.2
Double-precision is now an optional core feature instead of an extension.
Out of curiosity what is the difference? Extensions to OpenCL are optional but an "optional core feature" is also optional so I don't really see what the difference is.