--------------------------------------------------------------------------------------------------
change functions in gnumeric or - highly recommended - add variants instead:
some - old - info about programming gnumeric is in 'main_dir/doc/developer'.
assuming you already managed to compile gnumeric and have found that most functions reside in subdirs of 'plugins', there mostly in 'functions.c' ... poor mans simple approach:
take a function already existing there, if given together with it's 'help section' starting with sthg. like 'static GnmFuncHelp const help_function_name', most likely a block from one '/* info what function */' comment to the next one,
for first tests try an easy one, e.g. without subroutines like 'function_name1', and copy below itself,
in first step only change the function_name and! the 'help_function_name',
I. additional step to learn: add an appropriate entry in the 'GnmFuncDescriptor const xxxxxx_functions' section at the bottom of the file, copy from original function and adapt name and help_name,
II. add. step to learn: add an appropriate entry in '
plugin.xml.in' in that directory, copy from original function and change name, do not change plugin.xml, it's overwriten in compilation,
re-compile, and check if it's working, if not read compiler comments, if yes adapt to your needs,
be aware to use 'gnm_float' instead of 'double' or 'long double' as datatype, and - for most cases - 'gnm_code_function' instead of 'code_function' to enable datatype independent code, e.g. gnm_float x = gnm_pow( gnm_float y, gnm_float z ), instead of double x = pow( double y, double z ),
'numbers.h' in 'src' directory is the main dispatcher between double vs. long double and c-code vs. 'gnumeric substitutes in goffice' functions,
the rest is up to you, your knowledge in 'pure-C' programming, your luck in guessing the meaning of parameters and your patience to approach your goal in small steps,
what helped me immensely - after difficulties to get it running - is 'WHENCE' together with 'GG', 'SS' and 'confect' by John Denker, see
https://www.av8n.com/gnumeric/ , it allows several almost independent gnumeric installations side by side, and thus 'trial and error' while keeping an undisturbed original as reference.
hope that helps a little, hope I didn't miss steps ...
--------------------------------------------------------------------------------------------------
