From line_map comment at (libcpp/include/line-map.h)
/* Physical source file TO_FILE at line TO_LINE at column 0 is represented
by the logical START_LOCATION. TO_LINE+L at column C is represented by
START_LOCATION+(L*(1<<column_bits))+C, as long as C< (1<<column_bits),
What happens when column number is >= 128 ? This is PR 20907.
and the result_location is less than the next line_map's start_location.
(The top line is line 1 and the leftmost column is column 1; line/ column 0
means "entire file/line" or "unknown line/column" or "not applicable".)
INCLUDED_FROM is an index into the set that gives the line mapping
at whose end the current one was included. File(s) at the bottom
of the include stack have this set to -1. REASON is the reason for
creation of this line map, SYSP is one for a system header, two for
a C system header file that therefore needs to be extern "C"
protected in C++, and zero otherwise. */
Thanks, - Devang