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Simplify DAS.
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38933aa079
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@ -158,56 +158,22 @@ void das(
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uint8_t &al,
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ContextT &context
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) {
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/*
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(as modified by https://www.felixcloutier.com/x86/daa ...)
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old_AL ← AL;
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old_CF ← CF;
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CF ← 0;
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IF (((AL AND 0FH) > 9) or AF = 1)
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THEN
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AL ← AL - 6;
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CF ← old_CF OR CarryFromLastAddition; (* CF OR borrow from AL ← AL - 6 *)
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AF ← 1;
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ELSE
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AF ← 0;
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FI;
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IF ((old_AL > 99H) or old_CF = 1)
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THEN
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AL ← AL - 60H;
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CF ← 1;
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ELSE
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CF ← 0;
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FI;
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*/
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/*
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The CF and AF flags are set if the adjustment of the value results in a
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decimal carry in either digit of the result (see the “Operation” section above).
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The SF, ZF, and PF flags are set according to the result. The OF flag is undefined.
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*/
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const uint8_t old_al = al;
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const auto old_carry = context.flags.template flag<Flag::Carry>();
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context.flags.template set_from<Flag::Carry>(0);
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if((al & 0x0f) > 0x09 || context.flags.template flag<Flag::AuxiliaryCarry>()) {
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context.flags.template set_from<Flag::Carry>(old_carry | (al < 0x06));
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al -= 0x06;
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context.flags.template set_from<Flag::AuxiliaryCarry>(1);
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} else {
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context.flags.template set_from<Flag::AuxiliaryCarry>(0);
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}
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if(old_al > 0x99 || old_carry) {
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if(old_al > 0x99 || context.flags.template flag<Flag::Carry>()) {
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al -= 0x60;
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context.flags.template set_from<Flag::Carry>(1);
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} else {
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context.flags.template set_from<Flag::Carry>(0);
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}
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context.flags.template set_from<uint8_t, Flag::Zero, Flag::Sign, Flag::ParityOdd>(al);
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}
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}
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#endif /* BCD_h */
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