factorial example

emu/src/mem.cc

@@ -129,6 +129,8 @@ uint32_t Memory::read(uint32_t addr, enum size size)
         throw invl_arg(ERR_MSG("size = SIZE_SPECIAL"));
     }
 
+    logger->write("\t read %x", ret);
+
     return ret;
 }
 

emu/src/rpu32.cc

@@ -514,7 +514,7 @@ enum exec_status RPU32::execute()
         else if (BITSnm(instr.get_raw(), 6, 15) == 0b0100111011)
         {
             // JMP
-            decode_ea(instr.get_ea());
+            decode_ea(instr.get_ea(), instr.get_size());
 
             if (ea_state != EA_STATE_MEM)
                 throw invalid_instr(instr.get_raw());
@@ -525,7 +525,7 @@ enum exec_status RPU32::execute()
         else if (BITSnm(instr.get_raw(), 6, 15) == 0b0100111010)
         {
             // JSR
-            decode_ea(instr.get_ea());
+            decode_ea(instr.get_ea(), instr.get_size());
 
             if (ea_state != EA_STATE_MEM)
                 throw invalid_instr(instr.get_raw());
@@ -823,7 +823,7 @@ uint32_t RPU32::read_ea(uint8_t ea, enum size size)
                   ea);
 
     if (ea_state == EA_STATE_UNINIT)
-        decode_ea(ea);
+        decode_ea(ea, size);
 
     if (ea_state == EA_STATE_REG)
     {
@@ -876,7 +876,7 @@ void RPU32::write_ea(uint8_t ea, uint32_t data, enum size size)
                   data, ea);
 
     if (ea_state == EA_STATE_UNINIT)
-        decode_ea(ea);
+        decode_ea(ea, size);
 
     if (ea_state == EA_STATE_REG)
     {
@@ -903,7 +903,7 @@ void RPU32::write_ea(uint8_t ea, uint32_t data, enum size size)
     }
 }
 
-void RPU32::decode_ea(uint8_t ea)
+void RPU32::decode_ea(uint8_t ea, enum size size)
 {
     uint8_t reg       = BITSnm(ea, 0, 2);
     uint8_t mode      = BITSnm(ea, 3, 5);
@@ -937,7 +937,7 @@ void RPU32::decode_ea(uint8_t ea)
         offset   = regs->read(static_cast<reg_names>(reg + REG_A0), SIZE_LONG);
 
         ea_res = offset;
-        offset += (1 << instr.get_size()); // increment An by operand size
+        offset += (1 << size); // increment An by operand size
 
         regs->write(static_cast<reg_names>(reg + REG_A0), SIZE_LONG, offset);
         break;
@@ -946,7 +946,7 @@ void RPU32::decode_ea(uint8_t ea)
         ea_state = EA_STATE_MEM;
         offset   = regs->read(static_cast<reg_names>(reg + REG_A0), SIZE_LONG);
 
-        offset -= (1 << instr.get_size()); // decrement An by operand size
+        offset -= (1 << size); // decrement An by operand size
         ea_res = offset;
 
         regs->write(static_cast<reg_names>(reg + REG_A0), SIZE_LONG, offset);

emu/src/rpu32.h

@@ -83,7 +83,7 @@ private:
      */
     uint32_t read_ea(uint8_t ea, enum size size);
     void write_ea(uint8_t ea, uint32_t data, enum size size);
-    void decode_ea(uint8_t ea);
+    void decode_ea(uint8_t ea, enum size size);
     enum ea_state ea_state;
     uint32_t ea_res; // address or register number decoded from ea
 

emu/test.s

@@ -7,33 +7,58 @@ reset:
 .globl start
 start:
 	move.l #0x400, %a7 	/* setup the stack */
-	move.w #128, %d2
-	move.w #8, %d3
+	move.w #4, %d1
+	jsr factorial
 
-	jsr multiply
 	stop #0
 
+/* %d0 = %d1! */
+factorial:
+	cmpi.w #0, %d1
+	bne fskip1
+	move.w #1, %d0
+	rts
+
+fskip1:
+	cmpi.w #1, %d1
+	bne fskip2
+	move.w #1, %d0
+	rts
+
+fskip2:
+	move.w %d1, -(%a7)
+	subi #1, %d1
+
+	jsr factorial;
+
+	move.w (%a7)+, %d1
+	/* fact of (%d1 - 1) in %d0 */
+
+	jsr multiply
+	move.w %d2, %d0
+	rts
+	
 done:
 	move.w (%a7), %d0
 	rts
 
-multiply: 				/* %d4 = %d2 * %d3 */
-	cmpi.w #1, %d3 		/* %d2 + 1 = %d2, return */
-	bne notone
-	move.w %d2, %d4
+multiply: 				/* %d2 = %d0 * %d1 */
+	cmpi.w #1, %d1 		/* %d0 * 1 = %d0, return */
+	bne mskip1
+	move.w %d2, %d0
 	rts
 
-notone:
-	cmpi.w #0, %d3 		/* %d2 * 0 = 0 */
-	bne notzero
-	clr.w %d4
+mskip1:
+	clr.l %d2
+	cmpi.w #0, %d1 		/* %d0 * 0 = 0 */
+	bne mskip2
 	rts
 
-notzero:
-	subi.w #1, %d3
-	add.l %d2, %d4
-	cmpi.w #0, %d3
-	bne notzero 		/* Loop until done */
+mskip2:
+	add.l %d0, %d2
+	subi.w #1, %d1
+	cmpi.w #0, %d1
+	bne mskip2 			/* Loop until done */
 	rts
 
 .section .data