From 625e8d5e2e79502a5bf2e2e8cd444c53165115ec Mon Sep 17 00:00:00 2001
From: Eduard Urbach <admin@akyoto.dev>
Date: Mon, 24 Jun 2024 21:54:03 +0200
Subject: [PATCH] Improved x64 encoder

---
 src/build/Function.go                  | 12 +++++-----
 src/build/arch/x64/Add.go              |  2 +-
 src/build/arch/x64/Sub.go              |  2 +-
 src/build/arch/x64/numberToRegister.go | 33 ++++++++++++++------------
 src/build/arch/x64/sizeOf.go           | 20 ++++++++++++++++
 5 files changed, 46 insertions(+), 23 deletions(-)
 create mode 100644 src/build/arch/x64/sizeOf.go

diff --git a/src/build/Function.go b/src/build/Function.go
index 58e7cee..cc86f47 100644
--- a/src/build/Function.go
+++ b/src/build/Function.go
@@ -114,17 +114,17 @@ func (f *Function) CompileInstruction(line token.List) error {
 	}
 
 	if expr.Token.Kind == token.Operator {
+		name := expr.Children[0].Token.Text()
+		number, _ := strconv.Atoi(expr.Children[1].Token.Text())
+		register := f.Variables[name].Register
+
 		switch expr.Token.Text() {
 		case "+=":
-			name := expr.Children[0].Token.Text()
-			number, _ := strconv.Atoi(expr.Children[1].Token.Text())
-			f.Assembler.AddRegisterNumber(f.Variables[name].Register, number)
+			f.Assembler.AddRegisterNumber(register, number)
 			return nil
 
 		case "-=":
-			name := expr.Children[0].Token.Text()
-			number, _ := strconv.Atoi(expr.Children[1].Token.Text())
-			f.Assembler.SubRegisterNumber(f.Variables[name].Register, number)
+			f.Assembler.SubRegisterNumber(register, number)
 			return nil
 		}
 	}
diff --git a/src/build/arch/x64/Add.go b/src/build/arch/x64/Add.go
index d394968..f67094d 100644
--- a/src/build/arch/x64/Add.go
+++ b/src/build/arch/x64/Add.go
@@ -6,5 +6,5 @@ import (
 
 // 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)
+	return numRegReg(code, 0x83, 0x81, 0, byte(destination), number)
 }
diff --git a/src/build/arch/x64/Sub.go b/src/build/arch/x64/Sub.go
index af9511c..f2d5e9b 100644
--- a/src/build/arch/x64/Sub.go
+++ b/src/build/arch/x64/Sub.go
@@ -6,5 +6,5 @@ import (
 
 // 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)
+	return numRegReg(code, 0x83, 0x81, 0b101, byte(destination), number)
 }
diff --git a/src/build/arch/x64/numberToRegister.go b/src/build/arch/x64/numberToRegister.go
index 025a2ec..c67889e 100644
--- a/src/build/arch/x64/numberToRegister.go
+++ b/src/build/arch/x64/numberToRegister.go
@@ -1,24 +1,27 @@
 package x64
 
-import (
-	"math"
+// numRegReg encodes an instruction with up to two registers and a number parameter.
+func numRegReg(code []byte, opCode8 byte, opCode32 byte, reg byte, rm byte, number int) []byte {
+	w := byte(1)      // Indicates a 64-bit register.
+	r := byte(0)      // Extension to the "reg" field in ModRM.
+	x := byte(0)      // Extension to the SIB index field.
+	b := byte(0)      // Extension to the "rm" field in ModRM or the SIB base (r8 up to r15 use this).
+	mod := byte(0b11) // Direct addressing mode, no register offsets.
 
-	"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
+	if reg > 0b111 {
+		r = 1
+		reg &= 0b111
 	}
 
-	rex := REX(1, 0, 0, b)
-	modRM := ModRM(0b11, reg, byte(destination))
+	if rm > 0b111 {
+		b = 1
+		rm &= 0b111
+	}
 
-	if number >= math.MinInt8 && number <= math.MaxInt8 {
+	rex := REX(w, r, x, b)
+	modRM := ModRM(mod, reg, rm)
+
+	if sizeOf(number) == 1 {
 		return append(
 			code,
 			rex,
diff --git a/src/build/arch/x64/sizeOf.go b/src/build/arch/x64/sizeOf.go
new file mode 100644
index 0000000..8e6533b
--- /dev/null
+++ b/src/build/arch/x64/sizeOf.go
@@ -0,0 +1,20 @@
+package x64
+
+import "math"
+
+// sizeOf tells you how many bytes are needed to encode this number.
+func sizeOf(number int) int {
+	switch {
+	case number >= math.MinInt8 && number <= math.MaxInt8:
+		return 1
+
+	case number >= math.MinInt16 && number <= math.MaxInt16:
+		return 2
+
+	case number >= math.MinInt32 && number <= math.MaxInt32:
+		return 4
+
+	default:
+		return 8
+	}
+}