PetscErrorCode PetscBLASIntCast(a,&b) checks if the given PetscInt a will fit in a PetscBLASInt, if not it generates a PETSC_ERR_ARG_OUTOFRANGE error
MATLAB ships with BLAS and LAPACK that use 64 bit integers, for example if you run ./configure with, the option --with-blaslapack-lib=[/Applications/MATLAB_R2010b.app/bin/maci64/libmwblas.dylib,/Applications/MATLAB_R2010b.app/bin/maci64/libmwlapack.dylib]
MKL ships with both 32 and 64 bit integer versions of the BLAS and LAPACK. If you pass the flag -with-64-bit-blas-indices PETSc will link against the 64 bit version, otherwise it use the 32 bit version
OpenBLAS can be built to use 64 bit integers. The ./configure options --download-openblas -with-64-bit-blas-indices will build a 64 bit integer version
External packages such as hypre, ML, SuperLU etc do not provide any support for passing 64 bit integers to BLAS/LAPACK so cannot be used with PETSc when PETSc links against 64 bit integer BLAS/LAPACK. ./configure will generate an error if you attempt to link PETSc against any of these external libraries while using 64 bit integer BLAS/LAPACK.