Implemented subtraction

src/build/arch/x64/Add.go

@@ -1,18 +0,0 @@
-package x64
-
-import "git.akyoto.dev/cli/q/src/build/cpu"
-
-// AddRegNum8 adds a byte to the given register.
-func AddRegNum8(code []byte, destination cpu.Register, number uint8) []byte {
-	if destination >= 8 {
-		code = append(code, REX(0, 0, 0, 1))
-		destination -= 8
-	}
-
-	return append(
-		code,
-		0x83,
-		ModRM(0b11, 0b000, byte(destination)),
-		byte(number),
-	)
-}

src/build/arch/x64/Math.go

@@ -0,0 +1,15 @@
+package x64
+
+import (
+	"git.akyoto.dev/cli/q/src/build/cpu"
+)
+
+// AddRegNum adds a number to the given register.
+func AddRegNum(code []byte, destination cpu.Register, number int) []byte {
+	return numberToRegister(0x83, 0x81, 0b000, code, destination, number)
+}
+
+// SubRegNum subtracts a number from the given register.
+func SubRegNum(code []byte, destination cpu.Register, number int) []byte {
+	return numberToRegister(0x83, 0x81, 0b101, code, destination, number)
+}

src/build/arch/x64/numberToRegister.go

@@ -0,0 +1,41 @@
+package x64
+
+import (
+	"math"
+
+	"git.akyoto.dev/cli/q/src/build/cpu"
+)
+
+// numberToRegister encodes an instruction with a register and a number parameter.
+func numberToRegister(opCode8 byte, opCode32 byte, reg byte, code []byte, destination cpu.Register, number int) []byte {
+	b := byte(0)
+
+	if destination >= 8 {
+		b = 1
+		destination -= 8
+	}
+
+	rex := REX(1, 0, 0, b)
+	modRM := ModRM(0b11, reg, byte(destination))
+
+	if number >= math.MinInt8 && number <= math.MaxInt8 {
+		return append(
+			code,
+			rex,
+			opCode8,
+			modRM,
+			byte(number),
+		)
+	}
+
+	return append(
+		code,
+		rex,
+		opCode32,
+		modRM,
+		byte(number),
+		byte(number>>8),
+		byte(number>>16),
+		byte(number>>24),
+	)
+}