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switch effect multiplication to double and add extensive comment (re: 2012-03-23T03:06:39Z!alarantalara@gmail.com)

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Simon Forsyth 2012-03-26 05:01:16 +00:00
parent 6cdad25548
commit 7ab1d45c2e
1 changed files with 12 additions and 4 deletions
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16
src/unit_abilities.cpp
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@ -882,15 +882,23 @@ effect::effect(const unit_ability_list& list, int def, bool backstab) :
effect_list_.push_back(set_effect);
}
float multiplier = 1.0f;
float divisor = 1.0f;
/* Do multiplication with floating point values rather than integers
* We want two places of precision for each multiplier
* Using integers multiplied by 100 to keep precision causes overflow
* after 3-4 abilities for 32-bit values and ~8 for 64-bit
* Avoiding the overflow by dividing after each step introduces rounding errors
* that may vary depending on the order effects are applied
* As the final values are likely <1000 (always true for mainline), loss of less significant digits is not an issue
*/
double multiplier = 1.0;
double divisor = 1.0;
std::map<std::string,individual_effect>::const_iterator e, e_end;
for (e = values_mul.begin(), e_end = values_mul.end(); e != e_end; ++e) {
multiplier *= e->second.value/100.0f;
multiplier *= e->second.value/100.0;
effect_list_.push_back(e->second);
}
for (e = values_div.begin(), e_end = values_div.end(); e != e_end; ++e) {
divisor *= e->second.value/100.0f;
divisor *= e->second.value/100.0;
effect_list_.push_back(e->second);
}
int addition = 0;