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Emulator: Simplify isCarry(Subtraction) function

master
Riyyi 2 years ago
parent
059441c30a
commit
b48f308bfc
2 changed files with 24 additions and 59 deletions
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  1. 77
      src/cpu.cpp
  2. 6
      src/cpu.h

77
src/cpu.cpp
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@ -347,8 +347,8 @@ void CPU::adc8()
// Set flags
m_nf = 0;
m_hf = isCarry(m_a, register_, old_carry, 0xf);
m_cf = isCarry(m_a, register_, old_carry, 0xff);
m_hf = isCarry(0xf, m_a, register_, old_carry);
m_cf = isCarry(0xff, m_a, register_, old_carry);
// Add the value in r8 plus the carry flag to A
m_a = (m_a + register_ + old_carry) & 0xff;
@ -391,8 +391,8 @@ void CPU::add8()
// Set flags
m_nf = 0;
m_hf = isCarry(m_a, register_, 0x10);
m_cf = isCarry(m_a, register_, 0x100);
m_hf = isCarry(0xf, m_a, register_);
m_cf = isCarry(0xff, m_a, register_);
// Add the value in r8 to A
m_a = (m_a + register_) & 0xff;
@ -486,8 +486,8 @@ void CPU::cp()
// Zero flag
m_zf = ((m_a - register_) & 0xff) == 0;
m_nf = 1;
m_hf = isCarrySubtraction(m_a, register_, 0xf);
m_cf = isCarrySubtraction(m_a, register_, 0xff);
m_hf = isCarrySubtraction(0xf, m_a, register_);
m_cf = isCarrySubtraction(0xff, m_a, register_);
};
uint8_t opcode = pcRead();
@ -587,7 +587,7 @@ void CPU::dec8()
// Set flags
m_nf = 1;
m_hf = isCarrySubtraction(register_, 1, 0xf);
m_hf = isCarrySubtraction(0xf, register_, 1);
// Decrement value in register r8 by 1
register_ = (register_ - 1) & 0xff;
@ -627,7 +627,7 @@ void CPU::inc8()
// Set flags
m_nf = 0;
m_hf = isCarry(register_, 1, 0x10);
m_hf = isCarry(0xf, register_, 1);
// Increment value in register r8 by 1
register_ = (register_ + 1) & 0xff;
@ -713,8 +713,8 @@ void CPU::sbc8()
// Set flags
m_nf = 1;
m_hf = isCarrySubtraction(m_a, register_, old_carry, 0xf);
m_cf = isCarrySubtraction(m_a, register_, old_carry, 0xff);
m_hf = isCarrySubtraction(0xf, m_a, register_, old_carry);
m_cf = isCarrySubtraction(0xff, m_a, register_, old_carry);
// Subtract the value in r8 and the carry flag from A
m_a = (m_a - register_ - old_carry) & 0xff;
@ -759,8 +759,8 @@ void CPU::sub8()
// Set flags
m_nf = 1;
m_hf = isCarrySubtraction(m_a, register_, 0xf);
m_cf = isCarrySubtraction(m_a, register_, 0xff);
m_hf = isCarrySubtraction(0xf, m_a, register_);
m_cf = isCarrySubtraction(0xff, m_a, register_);
// Subtract the value in r8 from A
m_a = (m_a - register_) & 0xff;
@ -890,8 +890,8 @@ void CPU::addr16()
// Set flags
m_nf = 0;
m_hf = isCarry(hl(), register_, 0x1000);
m_cf = isCarry(hl(), register_, 0x10000);
m_hf = isCarry(0xfff, hl(), register_);
m_cf = isCarry(0xffff, hl(), register_);
// Add the value in r16 to HL
uint32_t data = (hl() + register_) & 0xffff;
@ -922,8 +922,8 @@ void CPU::adds8()
// Set flags
m_zf = 0;
m_nf = 0;
m_hf = isCarry(m_sp, signed_data, 0x10);
m_cf = isCarry(m_sp, signed_data, 0x100);
m_hf = isCarry(0xf, m_sp, signed_data);
m_cf = isCarry(0xff, m_sp, signed_data);
// Add the signed value s8 to SP
m_sp = m_sp + signed_data;
@ -1340,8 +1340,8 @@ void CPU::ldr16()
// Set flags
m_zf = 0;
m_nf = 0;
m_hf = isCarry(m_sp, signed_data, 0x10);
m_cf = isCarry(m_sp, signed_data, 0x100);
m_hf = isCarry(0xf, m_sp, signed_data);
m_cf = isCarry(0xff, m_sp, signed_data);
break;
}
case 0xf9: { // LD SP,HL
@ -1676,47 +1676,14 @@ uint32_t CPU::ffRead(uint32_t address)
return Emu::the().readMemory(address | (0xff << 8)) & 0xff;
}
bool CPU::isCarry(uint32_t lhs, uint32_t rhs, uint32_t limit_bit)
bool CPU::isCarry(uint32_t limit_bit, uint32_t first, uint32_t second, uint32_t third)
{
// limit_bit values:
// 8-bit half-carry = 0x10 or 16
// 8-bit carry = 0x100 or 256
// 16-bit half-carry = 0x1000 or 4096
// 16-bit carry = 0x10000 or 65536
// Example for 8-bit half-carry:
// 0b00111110 62 | 0b00111000 56
// 0b00100010 34 + | 0b00010001 17 +
// --------------- | ---------------
// 0b01100000 96 | 0b01001001 73
// |
// 0b00111110 62 | 0b00111000 56
// 0b00100010 34 ^ | 0b00010001 17 ^
// --------------- | ---------------
// 0b00011100 | 0b00101001
// 0b01100000 96 ^ | 0b01001001 73 ^
// --------------- | ---------------
// 0b01111100 | 0b01100000
// 0b00010000 16 & | 0b00010000 16 &
// --------------- | ---------------
// 0b00010000 = true! | 0b00000000 = false!
return (lhs ^ rhs ^ (lhs + rhs)) & limit_bit;
return (first & limit_bit) + (second & limit_bit) + (third & limit_bit) > limit_bit;
}
bool CPU::isCarry(uint32_t lhs, uint32_t middle, uint32_t rhs, uint32_t limit_bit)
bool CPU::isCarrySubtraction(uint32_t limit_bit, uint32_t lhs, uint32_t rhs, uint32_t rhs_extra)
{
return (lhs & limit_bit) + (middle & limit_bit) + (rhs & limit_bit) > limit_bit;
}
bool CPU::isCarrySubtraction(uint32_t lhs, uint32_t rhs, uint32_t limit_bit)
{
return (lhs & limit_bit) < (rhs & limit_bit);
}
bool CPU::isCarrySubtraction(uint32_t lhs, uint32_t middle, uint32_t rhs, uint32_t limit_bit)
{
return (lhs & limit_bit) < (middle & limit_bit) + (rhs & limit_bit);
return (lhs & limit_bit) < (rhs & limit_bit) + (rhs_extra & limit_bit);
}
// -----------------------------------------

6
src/cpu.h
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@ -123,10 +123,8 @@ private:
void ffWrite(uint32_t address, uint32_t value);
uint32_t ffRead(uint32_t address);
bool isCarry(uint32_t lhs, uint32_t rhs, uint32_t limit_bit);
bool isCarry(uint32_t lhs, uint32_t middle, uint32_t rhs, uint32_t limit_bit);
bool isCarrySubtraction(uint32_t lhs, uint32_t rhs, uint32_t limit_bit);
bool isCarrySubtraction(uint32_t lhs, uint32_t middle, uint32_t rhs, uint32_t limit_bit);
bool isCarry(uint32_t limit_bit, uint32_t first, uint32_t second, uint32_t third = 0x0);
bool isCarrySubtraction(uint32_t limit_bit, uint32_t lhs, uint32_t rhs, uint32_t rhs_extra = 0x0);
// Registers
uint32_t m_a { 0 }; // Accumulator

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