finished first row of opcodes

cpu/flags.go

@@ -1,6 +1,10 @@
 package cpu
 
-func Set8BitAddFlags(context op_context, byte1 byte, byte2 byte) byte {
+import (
+	"radu.macocian.me/goboy/cpu/operations"
+)
+
+func Add8BitsAndSetFlags(context op_context, byte1 byte, byte2 byte) byte {
 	result := uint16(byte1) + uint16(byte2)
 	halfcarry := (byte1&0x0F)+(byte2&0x0F) > 0x0F
 	context.cpu.SetNF(false)
@@ -17,3 +21,19 @@ func Add16BitsAndSetFlags(context op_context, op1 uint16, op2 uint16) uint16 {
 	context.cpu.SetCF(result > 0xFFFF)
 	return uint16(result)
 }
+
+func IncAndSetFlags(context op_context, op1 *byte) {
+	halfcarry := *op1&0x0F == 0x0F
+	context.cpu.SetNF(false)
+	context.cpu.SetHF(halfcarry)
+	context.cpu.SetZF(*op1 == byte(0))
+	operations.INC(op1)
+}
+
+func DecAndSetFlags(context op_context, op1 *byte) {
+	halfcarry := *op1&0x0F == 0x00
+	context.cpu.SetZF(*op1 == byte(0))
+	context.cpu.SetNF(true)
+	context.cpu.SetHF(halfcarry)
+	operations.DEC(op1)
+}

cpu/functions.go

@@ -34,48 +34,33 @@ func INCBC(context op_context) {
 
 // 0x04 INCB Increment the contents of register B by 1.
 func INCB(context op_context) {
-	if context.cpu.B&0x0F == 0x0F {
+	IncAndSetFlags(context, &context.cpu.B)
-		context.cpu.SetHF(true)
-	} else {
-		context.cpu.SetHF(false)
-	}
-	operations.INC(&context.cpu.B)
-
-	context.cpu.SetZF(context.cpu.B == byte(0))
-	context.cpu.SetNF(false)
 }
 
 // 0x05 DECB Decrement the contents of register B by 1.
 func DECB(context op_context) {
-	if context.cpu.B&0x0F == 0x00 {
+	DecAndSetFlags(context, &context.cpu.B)
-		context.cpu.SetHF(true)
-	} else {
-		context.cpu.SetHF(false)
-	}
-	operations.DEC(&context.cpu.B)
-
-	context.cpu.SetZF(context.cpu.B == byte(0))
-	context.cpu.SetNF(true)
 }
 
-// 0x06 LD8B Load the 8-bit immediate operand d8 into register B.
+// 0x06 LDBd8 Load the 8-bit immediate operand d8 into register B.
-func LD8B(context op_context) {
+func LDBd8(context op_context) {
-	operations.LD(&context.cpu.B, memory.Read8(uint(context.immediate)))
+	operations.LD(&context.cpu.B, byte(context.immediate))
 }
 
 // 0x07 RLCA Rotate the contents of register A to the left. The contents of bit 7 are placed in both the CY flag and bit 0 of register A.
 func RLCA(context op_context) {
-	a7 := context.cpu.A>>7 == 1
+	a7 := context.cpu.A >> 7
-	operations.Shift(&context.cpu.A)
+	operations.ShiftLeft(&context.cpu.A)
+	context.cpu.A = context.cpu.A | byte(a7)
 
 	context.cpu.SetZF(false)
 	context.cpu.SetNF(false)
 	context.cpu.SetHF(false)
-	context.cpu.SetCF(a7)
+	context.cpu.SetCF(a7 == 1)
 }
 
-// 0x08 LDA16 Store the lower byte of stack pointer SP at the address specified by the 16-bit immediate operand a16, and store the upper byte of SP at address a16 + 1.
+// 0x08 LDa16SP Store the lower byte of stack pointer SP at the address specified by the 16-bit immediate operand a16, and store the upper byte of SP at address a16 + 1.
-func LDA16(context op_context) {
+func LDa16SP(context op_context) {
 	operations.LDInMemory8(context.immediate, operations.GetLowerByte(context.cpu.SP))
 	operations.LDInMemory8(context.immediate+1, operations.GetHigherByte(context.cpu.SP))
 }
@@ -85,3 +70,41 @@ func ADDHLBC(context op_context) {
 	result := Add16BitsAndSetFlags(context, context.cpu.HL(), context.cpu.BC())
 	context.cpu.SetHL(result)
 }
+
+// 0x0A LDABC Load the 8-bit contents of memory specified by register pair BC into register A.
+func LDABC(context op_context) {
+	operations.LDFromMem(&context.cpu.A, uint(context.cpu.BC()))
+}
+
+// 0x0B DECBC Decrement the contents of register pair BC by 1.
+func DECBC(context op_context) {
+	operations.DEC16(&context.cpu.B, &context.cpu.C)
+}
+
+// 0x0C INCC Increment the contents of register C by 1.
+func INCC(context op_context) {
+	IncAndSetFlags(context, &context.cpu.C)
+}
+
+// 0x0D DECC Decrement the contents of register C by 1.
+func DECC(context op_context) {
+	DecAndSetFlags(context, &context.cpu.C)
+}
+
+// 0x0E LDCd8 Load the 8-bit immediate operand d8 into register C.
+func LDCd8(context op_context) {
+	context.cpu.C = byte(context.immediate)
+}
+
+// 0x0F RRRCA Rotate the contents of register A to the right. That is, the contents of bit 7 are copied to bit 6, and the previous contents of bit 6 (before the copy) are copied to bit 5. The same operation is repeated in sequence for the rest of the register. The contents of bit 0 are placed in both the CY flag and bit 7 of register A.
+func RRRCA(context op_context) {
+	a0 := context.cpu.A & 0x01
+	operations.ShiftRight(&context.cpu.A)
+	context.cpu.A = context.cpu.A | byte(a0)<<7
+
+	context.cpu.SetZF(false)
+	context.cpu.SetNF(false)
+	context.cpu.SetHF(false)
+	context.cpu.SetCF(a0 == 1)
+
+}

cpu/operations/shift.go

@@ -1,5 +1,9 @@
 package operations
 
-func Shift(r1 *byte) {
+func ShiftLeft(r1 *byte) {
 	*r1 = *r1 << 1
 }
+
+func ShiftRight(r1 *byte) {
+	*r1 = *r1 >> 1
+}

cpu/operations/shift_test.go

@@ -4,9 +4,9 @@ import (
 	"testing"
 )
 
-func TestShift(t *testing.T) {
+func TestShiftLeft(t *testing.T) {
 	r1 := byte(0b01010101)
-	Shift(&r1)
+	ShiftLeft(&r1)
 
 	expected := byte(0b10101010)
 	actual := r1
@@ -15,3 +15,15 @@ func TestShift(t *testing.T) {
 		t.Errorf("actual %x != expected %x", actual, expected)
 	}
 }
+
+func TestShiftRight(t *testing.T) {
+	r1 := byte(0b01010101)
+	ShiftLeft(&r1)
+
+	expected := byte(0b00101010)
+	actual := r1
+
+	if actual != expected {
+		t.Errorf("actual %x != expected %x", actual, expected)
+	}
+}

cpu/optable.go

@@ -7,6 +7,14 @@ var OpTable = [256]func(context op_context){
 	INCBC,   //0x03
 	INCB,    //0x04
 	DECB,    //0x05
-	LD8B,    //0x06
+	LDBd8,   //0x06
 	RLCA,    //0x07
+	LDa16SP, //0x08
+	ADDHLBC, //0x09
+	LDABC,   //0x0A
+	DECBC,   //0x0B
+	INCC,    //0x0C
+	DECC,    //0x0D
+	LDCd8,   //0x0E
+	RRRCA,   //0x0F
 }

journal/Day 3 - 2025.06.30.md

@@ -0,0 +1,7 @@
+# For the day:
+- Understand the cpu flags and when they are set
+
+# Conclusion
+- Wrote helper functions for setting the flags after addition/subtraction
+- Understood when the half-carry flag is set in addtions and subtractions
+- ?The carry flag is not set of INC and DEC operations?