guessing wrong driver for certain values of ROI_PAC raster

[scottstanie]

Expected behavior and actual behavior.

When saving a ".int" file for the ROI_PAC driver, the values of the raster seem to change gdal's ability to correctly guess the right driver. Large complex numbers fail, maybe by some heuristic that looks like the bytes of another driver. I'm not sure which it is guessing, since all it prints is ERROR 6: Unsupported compression

Steps to reproduce the problem.

$ ipython
Python 3.8.5 (default, Sep  4 2020, 07:30:14)
Type 'copyright', 'credits' or 'license' for more information
IPython 7.18.1 -- An enhanced Interactive Python. Type '?' for help.

In [1]: import numpy as np
# Large complex numbers seem to fail:
In [23]: arr = np.array([2180.8286 +4175.303j , 1256.5812 +2132.886j ,244.31543+2708.4495j, 
 841.01587+2190.2144j,1936.9266 +4414.4624j, 1360.6066 +2391.4644j], dtype=np.complex64)

In [24]: arr.tofile("test_roipac.int")

In [25]: with open("test_roipac.int.rsc", "w") as f:
    ...:     f.write("WIDTH  3\nFILE_LENGTH  2\n")
    ...:

In [26]: !gdalinfo test_roipac.int
ERROR 6: Unsupported compression
gdalinfo failed - unable to open 'test_roipac.int'.

# But the same array, with scaled down numbers, will work
In [27]: (arr / 1000).tofile("test_roipac.int")

In [28]: !gdalinfo test_roipac.int
Driver: ROI_PAC/ROI_PAC raster
Files: test_roipac.int
       test_roipac.int.rsc
Size is 3, 2
Corner Coordinates:
Upper Left  (    0.0,    0.0)
Lower Left  (    0.0,    2.0)
Upper Right (    3.0,    0.0)
Lower Right (    3.0,    2.0)
Center      (    1.5,    1.0)
Band 1 Block=3x1 Type=CFloat32, ColorInterp=Undefined

Operating system

Centos 7

GDAL version and provenance

Installed through conda:

In [29]: !gdalinfo --version
GDAL 3.2.1, released 2020/12/29