Backport #75642 Prevent div by zero crash in mana widget #76859
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Prevents division by zero crash when displaying widgets with defined break levels. 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 beng 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 CleverRaven#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 CleverRaven#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 CleverRaven#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 CleverRaven#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 CleverRaven#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 CleverRaven#8 0x0000555556aa5222 in custom_draw_func (args=...) at src/widget.cpp:970 CleverRaven#9 0x0000555555ec4360 in std::function<int(draw_args const&)>::operator() (this=0x555597eb1780, __args#0=...) at /usr/include/c++/14/bits/std_function.h:591 CleverRaven#10 game::draw_panels (this=this@entry=0x55555827ef50, force_draw=force_draw@entry=true) at src/game.cpp:4007 CleverRaven#11 0x0000555555eed1ac in game::draw (this=0x55555827ef50, ui=...) at src/game.cpp:3961 CleverRaven#12 0x00005555569a962c in ui_adaptor::redraw_invalidated () at src/ui_manager.cpp:440 CleverRaven#13 0x00005555569a96e9 in ui_adaptor::redraw () at src/ui_manager.cpp:345 CleverRaven#14 0x00005555569a9710 in ui_manager::redraw () at src/ui_manager.cpp:506 CleverRaven#15 0x0000555555dd0850 in do_turn () at src/do_turn.cpp:712 CleverRaven#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 ```
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Summary
Bugfixes "Prevent sidebar crash when trying to divide by zero"
Purpose of change
Describe the solution
Backport the crash bugfix
Just to be super duper extra safe, we still allow execution even if the value of var_range is negative. This might produce erroneous results, but it won't crash like div by zero.
Reason for the extra safety is that I thought it would prevent #76772, but @harakka was unable to reproduce. Still it appears that div-by-zero could happen on 0.H, so this is the narrowest possible backport.
Describe alternatives you've considered
Backporting the PR without any modification
More investigation into what caused/causes #76772
Testing
None personally
Additional context