From 0aa42d0d1ca829603ce7b6fd1e793a2a5a378828 Mon Sep 17 00:00:00 2001
From: Anton Lydike <me@antonlydike.de>
Date: Sat, 17 Apr 2021 22:59:37 +0200
Subject: [PATCH] implemented instructions beq, bne, blt, bge, bltu, bgeu,
 improved unsigned number handling

---
 riscemu/CPU.py     | 35 ++++++++++++++++++++++++++++++-----
 riscemu/helpers.py | 19 +++++++++++++++----
 2 files changed, 45 insertions(+), 9 deletions(-)

diff --git a/riscemu/CPU.py b/riscemu/CPU.py
index c1a66ad..b0eebf7 100644
--- a/riscemu/CPU.py
+++ b/riscemu/CPU.py
@@ -178,10 +178,20 @@ class CPU:
         INS_NOT_IMPLEMENTED(ins)
 
     def instruction_beq(self, ins: 'LoadedInstruction'):
-        INS_NOT_IMPLEMENTED(ins)
+        ASSERT_LEN(ins.args, 3)
+        reg1 = ins.get_reg(0)
+        reg2 = ins.get_reg(1)
+        dest = ins.get_imm(2)
+        if self.regs.get(reg1) == self.regs.get(reg2):
+            self.pc = dest
 
     def instruction_bne(self, ins: 'LoadedInstruction'):
-        INS_NOT_IMPLEMENTED(ins)
+        ASSERT_LEN(ins.args, 3)
+        reg1 = ins.get_reg(0)
+        reg2 = ins.get_reg(1)
+        dest = ins.get_imm(2)
+        if self.regs.get(reg1) != self.regs.get(reg2):
+            self.pc = dest
 
     def instruction_blt(self, ins: 'LoadedInstruction'):
         ASSERT_LEN(ins.args, 3)
@@ -192,13 +202,28 @@ class CPU:
             self.pc = dest
 
     def instruction_bge(self, ins: 'LoadedInstruction'):
-        INS_NOT_IMPLEMENTED(ins)
+        ASSERT_LEN(ins.args, 3)
+        reg1 = ins.get_reg(0)
+        reg2 = ins.get_reg(1)
+        dest = ins.get_imm(2)
+        if self.regs.get(reg1) >= self.regs.get(reg2):
+            self.pc = dest
 
     def instruction_bltu(self, ins: 'LoadedInstruction'):
-        INS_NOT_IMPLEMENTED(ins)
+        ASSERT_LEN(ins.args, 3)
+        reg1 = to_unsigned(ins.get_reg(0))
+        reg2 = to_unsigned(ins.get_reg(1))
+        dest = ins.get_imm(2)
+        if self.regs.get(reg1) < self.regs.get(reg2):
+            self.pc = dest
 
     def instruction_bgeu(self, ins: 'LoadedInstruction'):
-        INS_NOT_IMPLEMENTED(ins)
+        ASSERT_LEN(ins.args, 3)
+        reg1 = to_unsigned(ins.get_reg(0))
+        reg2 = to_unsigned(ins.get_reg(1))
+        dest = ins.get_imm(2)
+        if self.regs.get(reg1) >= self.regs.get(reg2):
+            self.pc = dest
 
     def instruction_j(self, ins: 'LoadedInstruction'):
         INS_NOT_IMPLEMENTED(ins)
diff --git a/riscemu/helpers.py b/riscemu/helpers.py
index 0441bfc..14226ec 100644
--- a/riscemu/helpers.py
+++ b/riscemu/helpers.py
@@ -35,10 +35,21 @@ def int_from_bytes(bytes, unsigned=False):
     for b in bytes:
         num = num << 8
         num += b
-    sign = num >> (len(bytes) * 8 - 1)
-    if sign and not unsigned:
-        return num - 2 ** (8 * len(bytes))
-    return num
+
+    if unsigned:
+        return num
+
+    return to_signed(num)
+
+
+def to_unsigned(num: int, bytes=4):
+    if num < 0:
+        return 2**(bytes * 8) - num
+
+
+def to_signed(num: int, bytes=4):
+    if num >> (bytes * 8 - 1):
+        return num - 2 ** (8 * bytes)
 
 
 # Colors