Data from extensive computations on class groups
of quadratic imaginary fields is available below.
It is organized by fundamental discriminant $-d$, and divided
into four groups based on congruences:

- $d\equiv 3\pmod 8$
- $d\equiv 7\pmod 8$
- $d\equiv 4\pmod {16}$
- $d\equiv 8\pmod {16}$

For each congruence class above, there are 4096 files, indexed from
$k=0$ to $k=4095$. The $k$th file contains data for
$k\cdot 2^{28} \leq |d| \lt (k+1)\cdot 2^{28}$. The files are named
accordingly, so the $k=12$ file for $d\equiv 7\pmod8$ is called

`cl7mod8.12.gz`

, the final extension because it has been
compressed with

`gzip`

. The compressed files range in size
from 50 to 200 megabytes.

After uncompressing with `gzip`

,
files have the following format:

- There is one line per field
- Discriminants for a given file are listed in order (in absolute value)
- If $-d_i$ is the $i$th discriminant for a file, line $i+1$ has the form
$a$ | $b$ | $c_1 c_2 \ldots c_t$ |

to signify that
- $d_{i+1} = d_i+m\cdot a$, ($m$ is the modulus for the file)
- $h(-d_{i+1}) = b$,
- invariant factors for the class group are $[c_1, c_2,\ldots, c_t]$.

In particular, $b=\prod_{j=1}^t c_j$.

### Getting files