Nonsensical shot damage calculation

[DragonWizard23]

Describe the bug

In the wield menu, the shot damage calculations don't always add up. The example in this save file is 0+27=24, but the inventory page for the gun itself has 26-2=24 damage.

Attach save file

Kamrar-trimmed.tar.gz

Steps to reproduce

1. Check the inventory of the attached save file.

Expected behavior

I expected that the math would check out.

Screenshots

Versions and configuration

• OS: Windows
  • OS Version: 10.0.26100.2894 (24H2)
• Game Version: 5ad4199 [64-bit]
• Graphics Version: Tiles
• Game Language: System language []
• Mods loaded: [
  Dark Days Ahead [dda],
  Disable NPC Needs [no_npc_food],
  Portal Storms Ignore NPCs [personal_portal_storms],
  Slowdown Fungal Growth [no_fungal_growth]
  ]

Additional context

This bug does not cause the game to crash.

[oosyrag]

Relevant code lives at

Cataclysm-DDA/src/game_inventory.cpp

Lines 1886 to 1907 in baa0ca2

	const int total_damage = loc->gun_damage( true ).total_damage();
	if( loc->has_ammo() ) {
	const int basic_damage = loc->gun_damage( false ).total_damage();
	const damage_instance &damage = loc->ammo_data()->ammo->damage;
	if( !damage.empty() ) {
	const float ammo_mult = damage.damage_units.front().unconditional_damage_mult;
	if( ammo_mult != 1.0f ) {
	return string_format( "%s<color_light_gray>*</color>%s <color_light_gray>=</color> %s",
	get_damage_string( basic_damage, true ),
	get_damage_string( ammo_mult, true ),
	get_damage_string( total_damage, true )
	);
	}
	}
	const int ammo_damage = damage.total_damage();
	return string_format( "%s<color_light_gray>+</color>%s <color_light_gray>=</color> %s",
	get_damage_string( basic_damage, true ),
	get_damage_string( ammo_damage, true ),
	get_damage_string( total_damage, true )
	);

and I'm presuming

Cataclysm-DDA/src/item.cpp

Lines 11057 to 11089 in baa0ca2

	damage_instance item::gun_damage( bool with_ammo, bool shot ) const
	{
	if( !is_gun() ) {
	return damage_instance();
	}
	units::length bl = barrel_length();
	damage_instance ret = type->gun->damage.di_considering_length( bl );
	for( const item *mod : gunmods() ) {
	ret.add( mod->type->gunmod->damage.di_considering_length( bl ) );
	}
	if( with_ammo && has_ammo() ) {
	if( shot ) {
	ret.add( ammo_data()->ammo->shot_damage.di_considering_length( bl ) );
	} else {
	ret.add( ammo_data()->ammo->damage.di_considering_length( bl ) );
	}
	}
	if( damage() > 0 ) {
	// TODO: This isn't a good solution for multi-damage guns/ammos
	for( damage_unit &du : ret ) {
	if( du.amount <= 1.0 ) {
	continue;
	}
	du.amount = std::max<float>( 1.0f, damage_adjusted_gun_damage( du.amount ) );
	}
	}
	return ret;
	}

but I don't know where to go from there or why basic_damage and ammo_damage values are incorrect, but total_damage is.