nth_msf

Find the position of the first bit set in mask, searching from (but not including) nth_bit downwards.

Bits are numbered from 0 (least significant) to sizeof(ulong) * 8 - 1 (31 or 63, usually). To start searching from the last bit, set nth_bit to -1 or GLIB_SIZEOF_LONG * 8.

Parameters:

mask	a ulong containing flags
nth_bit	the index of the bit to start the search from

Returns:

the index of the first bit set which is lower than nth_bit, or -1 if no lower bits are set