commit 8660646dc4d56e97f36595433b5c5737b8fcedb4
from: Witcher01 <witcher01+github@posteo.net>
date: Sun Aug  1 18:04:56 2021 UTC

added instruction SNE for regs

commit - 62fe7ccb10e71b355420d3fced24ad4d88998dc7
commit + 8660646dc4d56e97f36595433b5c5737b8fcedb4
blob - 5d06393b27541e3e57212e9d545981d5932699c5
blob + f8cdd4f86eb97f48254ef798d678cffcc6b3f0c3
--- src/chip8.rs
+++ src/chip8.rs
@@ -49,6 +49,8 @@ impl Chip8 {
         let kk = (instruction & 0x00FF) as u8;
         let x = ((instruction & 0x0F00) >> 8) as usize;
         let y = ((instruction & 0x00F0) >> 4) as usize;
+        // "least significant hex"
+        let lsh = instruction & 0x000F;
 
         match (instruction & 0xF000) >> 12 {
             0x0 => match nnn {
@@ -116,63 +118,78 @@ impl Chip8 {
                 // set Vx to Vx + kk
                 self.regs[x] += kk;
             },
-            0x8 => match instruction & 0x000F {
-                // LD Vx, Vy
-                0x0 => {
-                    self.regs[x] = self.regs[y];
-                },
-                // OR Vx, Vy
-                0x1 => {
-                    self.regs[x] |= self.regs[y];
-                },
-                // AND Vx, Vy
-                0x2 => {
-                    self.regs[x] &= self.regs[y];
-                },
-                // XOR Vx, Vy
-                0x3 => {
-                    self.regs[x] ^= self.regs[y];
-                },
-                // ADD Vx, Vy
-                0x4 => {
-                    // set VF by checking if an overflow occured
-                    match self.regs[x].checked_add(self.regs[y]) {
-                        Some(_) => self.regs[0xF] = 0,
-                        None => self.regs[0xF] = 1,
-                    };
-                    self.regs[x] += self.regs[y];
-                },
-                // SUB Vx, Vy
-                0x5 => {
-                    if self.regs[x] > self.regs[y] {
-                        self.regs[0xF] = 1;
-                    } else {
-                        self.regs[0xF] = 0;
+            0x8 => {
+                match lsh {
+                    // LD Vx, Vy
+                    0x0 => {
+                        self.regs[x] = self.regs[y];
+                    },
+                    // OR Vx, Vy
+                    0x1 => {
+                        self.regs[x] |= self.regs[y];
+                    },
+                    // AND Vx, Vy
+                    0x2 => {
+                        self.regs[x] &= self.regs[y];
+                    },
+                    // XOR Vx, Vy
+                    0x3 => {
+                        self.regs[x] ^= self.regs[y];
+                    },
+                    // ADD Vx, Vy
+                    0x4 => {
+                        // set VF by checking if an overflow occured
+                        match self.regs[x].checked_add(self.regs[y]) {
+                            Some(_) => self.regs[0xF] = 0,
+                            None => self.regs[0xF] = 1,
+                        };
+                        self.regs[x] += self.regs[y];
+                    },
+                    // SUB Vx, Vy
+                    0x5 => {
+                        if self.regs[x] > self.regs[y] {
+                            self.regs[0xF] = 1;
+                        } else {
+                            self.regs[0xF] = 0;
+                        }
+                        self.regs[x] -= self.regs[y];
+                    },
+                    // SHR Vx {, Vy}
+                    0x6 => {
+                        self.regs[0xF] = self.regs[x] & 0x01;
+                        self.regs[x] /= 2;
+                    },
+                    // SUBN Vx, Vy
+                    0x7 => {
+                        if self.regs[y] > self.regs[x] {
+                            self.regs[0xF] = 1;
+                        } else {
+                            self.regs[0xF] = 0;
+                        }
+                        self.regs[x] = self.regs[y] - self.regs[x];
+                    },
+                    // SHL Vx {, Vy}
+                    0xE => {
+                        self.regs[0xF] = self.regs[x] & 0x70;
+                        self.regs[x] *= 2;
+                    },
+                    _ => {
+                        return Err(format!("{:#06x}: not an instruction", instruction));
                     }
-                    self.regs[x] -= self.regs[y];
-                },
-                // SHR Vx {, Vy}
-                0x6 => {
-                    self.regs[0xF] = self.regs[x] & 0x01;
-                    self.regs[x] /= 2;
-                },
-                // SUBN Vx, Vy
-                0x7 => {
-                    if self.regs[y] > self.regs[x] {
-                        self.regs[0xF] = 1;
-                    } else {
-                        self.regs[0xF] = 0;
-                    }
-                    self.regs[x] = self.regs[y] - self.regs[x];
-                },
-                // SHL Vx {, Vy}
-                0xE => {
-                    self.regs[0xF] = self.regs[x] & 0x70;
-                    self.regs[x] *= 2;
-                },
-                _ => {
+                };
+                self.pc += 2;
+            },
+            // SNE Vx, Vy
+            0x9 => {
+                if lsh != 0 {
                     return Err(format!("{:#06x}: not an instruction", instruction));
                 }
+
+                if self.regs[x] != self.regs[y] {
+                    self.pc += 4;
+                } else {
+                    self.pc += 2;
+                }
             },
             _ => {
                 return Err(format!("{:#06x}: not an instruction", instruction));