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[as/286] Add reg8_reg8()

This function implements 8 bit register to register instructions.
It hasn't been tested, but it should work.

--- a/as/target/x86/ins.c

+++ b/as/target/x86/ins.c

@@ -6,6 +6,15 @@

 #include "../../as.h"

 #include "proc.h"

+#define addrbyte(mod, reg, rm) ((mod) << 6 | (reg) << 3 | (rm))

+

+enum addr_mode {

+	MEM_MODE   = 0,

+	MEM8_MODE  = 1,

+	MEM16_MODE = 2,

+	REG_MODE   = 3,

+};

+

 static int

 getclass(Node *np)

 {

@@ -220,4 +229,33 @@

 Node *

 moperand(void)

 {

+}

+

+static int

+reg8toint(Node *np)

+{

+	switch (np->sym->value) {

+	case AREG_AL: return 0;

+	case AREG_CL: return 1;

+	case AREG_DL: return 2;

+	case AREG_BL: return 3;

+	case AREG_AH: return 4;

+	case AREG_CH: return 5;

+	case AREG_DH: return 6;

+	case AREG_BH: return 7;

+	default:      abort();

+	}

+}

+

+void

+reg8_reg8(Op *op, Node **args)

+{

+	int src, dst;

+	char buf[2];

+

+	src = reg8toint(args[0]);

+	dst = reg8toint(args[1]);

+	buf[0] = op->bytes[0];

+	buf[1] = addrbyte(REG_MODE, src, dst);

+	emit(buf, 2);

 }

--- a/as/target/x86/rules.dat

+++ b/as/target/x86/rules.dat

@@ -1,5 +1,5 @@

-reg8	AREG8

-reg16	AREG16

+reg8	AREG_R8CLASS

+reg16	AREG_R16CLASS

 imm8	AIMM8

 imm16	AIMM16

 imm32	AIMM32

--- a/as/target/x86/x86.dat

+++ b/as/target/x86/x86.dat

@@ -24,4 +24,4 @@

 # 8 bit arithmetic operations

-#ADDB	reg8,reg8	2	0x00,0xc0	reg2reg	I286,I386,AMD64

+ADDB	reg8,reg8	2	0x00	reg8_reg8	I286,I386,AMD64