Prevent div by zero crash in mana widget

[inogenous]

Summary

Bugfixes "Prevent div by zero crash in mana widget"

Purpose of change

Prevents division by zero crash when displaying widgets with defined break levels.

Fixes #75566 . Fixes #72474 .

Describe the solution

Example of where previous crash from div-by-zero happened:

• Provided save used the zenfs_thick_sidebar, which includes widget zenfs_mana_bar_14_no_label that defines break levels.
• When running the provided save, mana value is usually at v=201 with min=0 max=201.
• Those values are computed by known_magic::max_mana where internal values are bionic_penalty=999 mana_base=1000 int_bonus=200.
• But when int falls (because of tiredness), then known_magic::max_mana will return 0 because int_bonus=-100.
• This leads to _var_max=0 in widget::value_color and thus var_range=0 which causes the div by zero.

Backtrace of previous crash being fixed:

Thread 1 "cataclysm-tiles" received signal SIGFPE, Arithmetic exception.
0x0000555556a9c54e in widget::value_color (this=this@entry=0x7fffffffb8d8, value=value@entry=201) at src/widget.cpp:1310
1310            const int value_offset = ( 100 * ( value - _var_min ) ) / var_range;

(gdb) bt
 #0  0x0000555556a9c54e in widget::value_color (this=this@entry=0x7fffffffb8d8, value=value@entry=201) at src/widget.cpp:1310
 #1  0x0000555556aa37dc in widget::color_value_string[abi:cxx11](int, int) (this=this@entry=0x7fffffffb8d8, value=201, width_max=width_max@entry=14) at src/widget.cpp:1262
 #2  0x0000555556aa38ca in widget::show[abi:cxx11](avatar const&, unsigned int) (this=this@entry=0x7fffffffb8d8, ava=..., max_width=max_width@entry=14) at src/widget.cpp:890
 #3  0x0000555556aa497f in widget::layout[abi:cxx11](avatar const&, unsigned int, int, bool) (this=this@entry=0x7fffffffb8d8, ava=..., max_width=<optimized out>, label_width=label_width@entry=0, skip_pad=false) at src/widget.cpp:1834
 #4  0x0000555556aa42c2 in widget::layout[abi:cxx11](avatar const&, unsigned int, int, bool) (this=this@entry=0x7fffffffbe88, ava=..., max_width=<optimized out>, label_width=label_width@entry=9, skip_pad=false) at src/widget.cpp:1794
 #5  0x0000555556aa3cfa in widget::layout[abi:cxx11](avatar const&, unsigned int, int, bool) (this=this@entry=0x7fffffffc438, ava=..., max_width=<optimized out>, label_width=label_width@entry=0, skip_pad=false) at src/widget.cpp:1724
 #6  0x0000555556aa42c2 in widget::layout[abi:cxx11](avatar const&, unsigned int, int, bool) (this=this@entry=0x7fffffffc9e8, ava=..., max_width=<optimized out>, label_width=label_width@entry=0, skip_pad=false) at src/widget.cpp:1794
 #7  0x0000555556aa42c2 in widget::layout[abi:cxx11](avatar const&, unsigned int, int, bool) (this=this@entry=0x555562c47160, ava=..., max_width=<optimized out>, max_width@entry=64, label_width=<optimized out>, skip_pad=skip_pad@entry=false) at src/widget.cpp:1794
 #8  0x0000555556aa5222 in custom_draw_func (args=...) at src/widget.cpp:970
 #9  0x0000555555ec4360 in std::function<int(draw_args const&)>::operator() (this=0x555597eb1780, __args#0=...) at /usr/include/c++/14/bits/std_function.h:591
 #10 game::draw_panels (this=this@entry=0x55555827ef50, force_draw=force_draw@entry=true) at src/game.cpp:4007
 #11 0x0000555555eed1ac in game::draw (this=0x55555827ef50, ui=...) at src/game.cpp:3961
 #12 0x00005555569a962c in ui_adaptor::redraw_invalidated () at src/ui_manager.cpp:440
 #13 0x00005555569a96e9 in ui_adaptor::redraw () at src/ui_manager.cpp:345
 #14 0x00005555569a9710 in ui_manager::redraw () at src/ui_manager.cpp:506
 #15 0x0000555555dd0850 in do_turn () at src/do_turn.cpp:712
 #16 0x00005555557a138d in main (argc=<optimized out>, argv=<optimized out>) at src/main.cpp:873

(gdb) print var_range
$1 = 0
(gdb) print value
$2 = 201
(gdb) print _var_min
$3 = 0
(gdb) print _var_max
$4 = 0

Describe alternatives you've considered

Testing

• Can reliably reproduce the div-by-zero using the save (and config) in Arithmetical error CTD during long-term tasks #75566 . On this branch, the crash can no longer be reproduced.

Additional context

Other conditionals in this method are already checking var_range > 0.

[RenechCDDA]

I think this may resolve #72474 as well, though my past comments note that may have been due to power storage and not mana.

[inogenous]

I think this may resolve #72474 as well

Oh that's great. Yes, you're right! I can reliably reproduce that issue on master, but on this branch I am not able to reproduce the crash. Also, it might actually be the mana bar in that issue also, since the amount of mana is inversely affected by amount of bionic energy, and max mana eventually reaches 0 when bionic power increases.

Thanks for having such good memory @RenechCDDA ! I'll update the description with fixes for this issue also. Thanks!