[Fontconfig] fc-query output

[Dave Pawson]

  I'm trying to learn a little more about fonts on my Linux box
for use with xsl-fo.

My current problem is trying to find out if a Unicode code point is
present in any given font.

fc-query dumps a (btree?) list of the code points supported (AFAICT).
I'm looking for a way of testing if  U+1234 is present in font xxx.otf
so that I give a yes/no if the code point is present in this font?k

I can capture the charset: section of fc-query output
but I'm looking for an algorithm /explanation of the format of the section?

E.g for one of my fonts...
       charset:
       0000: 00000000 ffffffff ffffffff 7fffffff 00000000 ffffdfef
bfffffff bfffffff
       0001: 00000000 00020000 000c0006 61000003 00040000 00000000
00000000 00000000
       0002: 00000000 00000000 00000000 00000000 00000000 00000000
3f0000c0 00000000
       0003: 00000000 00000000 00000000 00000000 00000000 00000200
00000001 00000000
       0020: 77180000 06010047 00000010 00000000 00000000 00001000
00000000 00000000
       0021: 00000000 00000004 00000000 00000000 00000000 00000000
00000000 00000000
       0022: 44068044 00000800 00000100 00000031 00000000 00000000
00000000 00000000
       0025: 00000000 00000000 00000000 00000000 00000000 00000000
00000400 00000000
       00fb: 00000006 00000000 00000000 00000000 00000000 00000000
00000000 00000000

Any pointers as to how to interpret this would be appreciated.
I've pulled the fontconfig source... but my C is 30 years old and rusty.