Fast-food binary formatΒΆ

The fast-food format is a fortran binary format – all fields are surrounded with 4 bytes padding. These value of these padding bytes is the number of bytes of data contained in between the padding bytes. For example, to write out 20 bytes of data in a fast-food file format would require a total of 4+20+4=28 bytes. The first and last 4 bytes of the file will contain the value 20 – showing that 20 bytes of real data are contained in between the two paddings.

The fast-food file consists of a header:

int idat[5];
float fdat[9];
float znow;

For the purposes of these correlation function codes, the only useful quantity is idat[1] which contains N – the number of particles in the file. The rest can simply filled with 0.

After this header, the actual X/Y/Z values are stored. The first 4 bytes after the header contains 4*N for float precision or 8*N for double precision where N=idat[1], is the number of particles in the file. After all of the X values there will be another 4 bytes containing 4*N or 8*N.


Even when the X/Y/Z arrays are written out in double-precision, the padding is still 4 bytes. The blocks for Y/Z similarly follow after the X block.