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Fixed the modulo operator for negative integers
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* this changes the behavior of vanilla modulo operator to use signed
integer division to match how the fixed division operator works.
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@NovaRain
NovaRain committed Jan 25, 2024
1 parent 4f786f3 commit b8fe8cb
Showing 1 changed file with 6 additions and 3 deletions.
9 changes: 6 additions & 3 deletions sfall/Modules/BugFixes.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -3305,13 +3305,16 @@ void BugFixes::init() {
SafeWriteBatch<WORD>(0x04DB, { // fild 64bit > fild 32bit
0x46A3A8, 0x46A3F4, // op_mul_
0x46A4E7, 0x46A566, // op_div_
0x46A280, 0x46A2CD, // op_sub_
0x46A280, 0x46A2CD // op_sub_
});

// Fix for vanilla division operator treating negative integers as unsigned
// Fix for vanilla division and modulo operators treating negative integers as unsigned
//if (IniReader::GetConfigInt("Misc", "DivisionOperatorFix", 1)) {
dlogr("Applying division operator fix.", DL_FIX);
SafeWrite32(0x46A51D, 0xFBF79990); // xor edx, edx; div ebx > cdq; idiv ebx
SafeWriteBatch<DWORD>(0x90FBF799, { // xor edx, edx; div ebx > cdq; idiv ebx
0x46A51D, // op_div_
0x46A669 // op_mod_
});
//}

//if (IniReader::GetConfigInt("Misc", "SpecialUnarmedAttacksFix", 1)) {
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@NovaRain
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@NovaRain NovaRain commented on b8fe8cb Jan 25, 2024 •
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Kinda forgot the modulo when we fixed the division operator in 4.2.3.
Test script code:

variable i;
for (i := -5; i <= 5; i++) begin
   display_msg("Div/Mod test pos: " + i + ", div: " + (i / 3) + ", mod: " + (i % 3));
   display_msg("Div/Mod test neg: " + i + ", div: " + (i / -3) + ", mod: " + (i % -3));
end

Results:

// before                                // now
Div/Mod test pos: -5, div: -1, mod: 2    Div/Mod test pos: -5, div: -1, mod: -2
Div/Mod test neg: -5, div: 1, mod: -5    Div/Mod test neg: -5, div: 1, mod: -2
Div/Mod test pos: -4, div: -1, mod: 0    Div/Mod test pos: -4, div: -1, mod: -1
Div/Mod test neg: -4, div: 1, mod: -4    Div/Mod test neg: -4, div: 1, mod: -1
Div/Mod test pos: -3, div: -1, mod: 1    Div/Mod test pos: -3, div: -1, mod: 0
Div/Mod test neg: -3, div: 1, mod: 0     Div/Mod test neg: -3, div: 1, mod: 0
Div/Mod test pos: -2, div: 0, mod: 2     Div/Mod test pos: -2, div: 0, mod: -2
Div/Mod test neg: -2, div: 0, mod: 1     Div/Mod test neg: -2, div: 0, mod: -2
Div/Mod test pos: -1, div: 0, mod: 0     Div/Mod test pos: -1, div: 0, mod: -1
Div/Mod test neg: -1, div: 0, mod: 2     Div/Mod test neg: -1, div: 0, mod: -1
Div/Mod test pos: 0, div: 0, mod: 0      Div/Mod test pos: 0, div: 0, mod: 0
Div/Mod test neg: 0, div: 0, mod: 0      Div/Mod test neg: 0, div: 0, mod: 0
Div/Mod test pos: 1, div: 0, mod: 1      Div/Mod test pos: 1, div: 0, mod: 1
Div/Mod test neg: 1, div: 0, mod: 1      Div/Mod test neg: 1, div: 0, mod: 1
Div/Mod test pos: 2, div: 0, mod: 2      Div/Mod test pos: 2, div: 0, mod: 2
Div/Mod test neg: 2, div: 0, mod: 2      Div/Mod test neg: 2, div: 0, mod: 2
Div/Mod test pos: 3, div: 1, mod: 0      Div/Mod test pos: 3, div: 1, mod: 0
Div/Mod test neg: 3, div: -1, mod: 3     Div/Mod test neg: 3, div: -1, mod: 0
Div/Mod test pos: 4, div: 1, mod: 1      Div/Mod test pos: 4, div: 1, mod: 1
Div/Mod test neg: 4, div: -1, mod: 4     Div/Mod test neg: 4, div: -1, mod: 1
Div/Mod test pos: 5, div: 1, mod: 2      Div/Mod test pos: 5, div: 1, mod: 2
Div/Mod test neg: 5, div: -1, mod: 5     Div/Mod test neg: 5, div: -1, mod: 2

At least now they match the results from MSVC.

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