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Simplify DAS.

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This commit is contained in:
Thomas Harte 2023-11-08 22:19:51 -05:00
parent 38933aa079
commit 6b666bc92a
1 changed files with 2 additions and 36 deletions
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38
InstructionSets/x86/Implementation/BCD.hpp
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@ -158,56 +158,22 @@ void das(
uint8_t &al, uint8_t &al,
ContextT &context ContextT &context
) { ) {
/*
(as modified by https://www.felixcloutier.com/x86/daa ...)
old_AL ← AL;
old_CF ← CF;
CF ← 0;
IF (((AL AND 0FH) > 9) or AF = 1)
THEN
AL ← AL - 6;
CF ← old_CF OR CarryFromLastAddition; (* CF OR borrow from AL ← AL - 6 *)
AF ← 1;
ELSE
AF ← 0;
FI;
IF ((old_AL > 99H) or old_CF = 1)
THEN
AL ← AL - 60H;
CF ← 1;
ELSE
CF ← 0;
FI;
*/
/*
The CF and AF flags are set if the adjustment of the value results in a
decimal carry in either digit of the result (see the “Operation” section above).
The SF, ZF, and PF flags are set according to the result. The OF flag is undefined.
*/
const uint8_t old_al = al; const uint8_t old_al = al;
const auto old_carry = context.flags.template flag<Flag::Carry>();
context.flags.template set_from<Flag::Carry>(0);
if((al & 0x0f) > 0x09 || context.flags.template flag<Flag::AuxiliaryCarry>()) { if((al & 0x0f) > 0x09 || context.flags.template flag<Flag::AuxiliaryCarry>()) {
context.flags.template set_from<Flag::Carry>(old_carry | (al < 0x06));
al -= 0x06; al -= 0x06;
context.flags.template set_from<Flag::AuxiliaryCarry>(1); context.flags.template set_from<Flag::AuxiliaryCarry>(1);
} else {
context.flags.template set_from<Flag::AuxiliaryCarry>(0);
} }
if(old_al > 0x99 || old_carry) { if(old_al > 0x99 || context.flags.template flag<Flag::Carry>()) {
al -= 0x60; al -= 0x60;
context.flags.template set_from<Flag::Carry>(1); context.flags.template set_from<Flag::Carry>(1);
} else {
context.flags.template set_from<Flag::Carry>(0);
} }
context.flags.template set_from<uint8_t, Flag::Zero, Flag::Sign, Flag::ParityOdd>(al); context.flags.template set_from<uint8_t, Flag::Zero, Flag::Sign, Flag::ParityOdd>(al);
} }
} }
#endif /* BCD_h */ #endif /* BCD_h */