FcCharSetFirstPage man page
FcCharSetFirstPage — Start enumerating charset contents
#include <fontconfig/fontconfig.h> FcChar32 FcCharSetFirstPage (const FcCharSet *a, FcChar32[FC_CHARSET_MAP_SIZE] map, FcChar32 *next);
Builds an array of bits in map marking the first page of Unicode coverage of a. *next is set to contains the base code point for the next page in a. Returns the base code point for the page, or FC_CHARSET_DONE if a contains no pages. As an example, if FcCharSetFirstPage returns 0x300 and fills map with
0xffffffff 0xffffffff 0x01000008 0x44300002 0xffffd7f0 0xfffffffb 0xffff7fff 0xffff0003
Then the page contains code points 0x300 through 0x33f (the first 64 code points on the page) because map and map both have all their bits set. It also contains code points 0x343 (0x300 + 32*2 + (4-1)) and 0x35e (0x300 + 32*2 + (31-1)) because map has the 4th and 31st bits set. The code points represented by map and later are left as an excercise for the reader ;).