ds318.1 GFDL Cyber 205 Format

GFDL data in Cyber 205 format has the following file structure:

Each record in a file begins with a 64-bit control word. The length of the record in bytes is in the right-most 24-bits of the control word. However, if this record length is not a multiple of eight, it must be increased to the nearest number that is a multiple of eight to get the true record length. The record length does NOT include the 8 bytes used for the control word.

There are two types of records: a header record and a data record. A header record is 800 bytes long. It is not known how to decode this type of record. A data record is either 680 (for the R30, 170 variable-runs) or 688 (for the R15 QFLUX 171-variable runs) bytes long. Within the data record, each value V is contained in a 32-bit Cyber float, as follows:

EEEEEEEEMMMMMMMMMMMMMMMMMMMMMMMM

where:
EEEEEEEE is the two's complement¹ exponent E,
MMMMMMMMMMMMMMMMMMMMMMMM is the two's complement² mantissa M, and
the value V = M * 2<sup>E

1</sup> if (E >= 128) E=E-256
² if (M >= 8388608) M=M-16777216

The total number of records in a file depends on the size of the grid and the number of time steps. There is one data record containing values for all variables at each gridpoint and time step, and one header record ahead of all the data records for a single grid.