implemented branching operations

STATE.md

@@ -21,7 +21,9 @@
   - step dispatch shell + trace in nestest format
   - set_test_start for the nestest harness
 - nestest harness working (main.rs): loads nestest.nes, runs from $C000 with CYC:7, dumps trace to ours.log
-- First 5 trace lines match the nestest reference log exactly (PC, regs, P, SP, CYC), then it panics on the next unimplemented opcode (JSR 0x20), which names the next target
+- Batch 1 done (subroutines + stack): JSR, RTS, PHA, PLA, PHP, PLP, RTI, BRK, plus NOP and SEC as quick wins. Verified SP:FD->FB across JSR (push high-then-low works)
+- Trace now matches the nestest reference log through line 8 (C72E SEC, CYC:29). Next panic is on BCS 0xB0 at line 9 (Batch 2)
+- trace bytes are length-aware via opcode_len (fixed-width byte field, columns align for awk diff)
 
 ## Next
 
@@ -29,8 +31,8 @@ Finish the official CPU. Nestest analysis findings: the full 8991-line log tests
 
 CPU implementation batches (by family, ordered by nestest log frequency):
 
-- Batch 1 - Subroutines + stack: JSR 0x20 (push ret-1 high then low), RTS 0x60 (pop low then high), PHA 0x48, PLA 0x68, PHP 0x08, PLP 0x28 (B-flag on push rule), RTI 0x40, BRK 0x00
+- Batch 1 - DONE (see Done section)
-- Batch 2 - Branches (all 8): BEQ F0, BNE D0, BCC 90, BCS B0, BPL 10, BMI 30, BVC 50, BVS 70. One shared method per flag. +1 cycle if taken, +1 more if target crosses page
+- Batch 2 - Branches (all 8): BEQ F0, BNE D0, BCC 90, BCS B0, BPL 10, BMI 30, BVC 50, BVS 70. One shared method per flag. +1 cycle if taken, +1 more if target crosses page. Next up
 - Batch 3 - Loads: LDA 8 modes, LDX 5 modes, LDY 5 modes (share load + set_zp_flags)
 - Batch 4 - Stores: STA 7 modes, STX 3, STY 3 (share store core, no flag changes)
 - Batch 5 - Compares: CMP 8 modes, CPX 3, CPY 3 (set C/Z/N, no store)

ours.log

@@ -6,4 +6,6 @@ C5FB  86 11    A:00 X:00 Y:00 P:26 SP:FD CYC:18
 C5FD  20 2D C7  A:00 X:00 Y:00 P:26 SP:FD CYC:21
 C72D  EA       A:00 X:00 Y:00 P:26 SP:FB CYC:27
 C72E  38       A:00 X:00 Y:00 P:26 SP:FB CYC:29
-C72F  B0       A:00 X:00 Y:00 P:27 SP:FB CYC:31
+C72F  B0 04    A:00 X:00 Y:00 P:27 SP:FB CYC:31
+C735  EA       A:00 X:00 Y:00 P:27 SP:FB CYC:34
+C736  18       A:00 X:00 Y:00 P:27 SP:FB CYC:36

src/cpu.rs

@@ -109,6 +109,14 @@ impl Cpu {
             0x00 => self.brk_imp(bus),
             0xEA => self.nop_imp(bus),
             0x38 => self.sec_imp(bus),
+            0x90 => self.bcc_rel(bus),
+            0xB0 => self.bcs_rel(bus),
+            0xF0 => self.beq_rel(bus),
+            0xD0 => self.bne_rel(bus),
+            0x10 => self.bpl_rel(bus),
+            0x30 => self.bmi_rel(bus),
+            0x50 => self.bvc_rel(bus),
+            0x70 => self.bvs_rel(bus),
             _ => panic!("illegal/unkown opcode {opcode:#04X} at {:#06X}", self.pc.wrapping_sub(1)),
         };
         self.cycles += cycles as u64;
@@ -191,6 +199,21 @@ impl Cpu {
         self.pc.wrapping_add((offset as i8) as u16) // sign-extend + add, this allows to move the PC backwards
     }
 
+    // Branching helper for general Branch operations
+
+    fn branch(&mut self, bus: &mut impl Bus, condition: bool) -> u8 {
+        let target: u16 = self.address_rel(bus);
+        if !condition {
+            return 2;
+        }
+        let mut cycles: u8 = 3;
+        if (self.pc & 0xFF00) != (target & 0xFF00) {
+            cycles += 1;
+        }
+        self.pc = target;
+        cycles
+    }
+
     // NES 6502 opcode -> functions
     fn jmp_abs(&mut self, bus: &mut impl Bus) -> u8 { // 0x4C, 3 bytes, 3 cycles
         self.pc = self.fetch16(bus);
@@ -274,6 +297,16 @@ impl Cpu {
         2
     }
 
+    // all branching alternatives here all 2 bytes
+    fn bcs_rel(&mut self, bus: &mut impl Bus) -> u8 { self.branch(bus, self.flag(FLAG_CARRY)) } // 0x90
+    fn bcc_rel(&mut self, bus: &mut impl Bus) -> u8 { self.branch(bus, !self.flag(FLAG_CARRY)) } // 0xB0
+    fn beq_rel(&mut self, bus: &mut impl Bus) -> u8 { self.branch(bus, self.flag(FLAG_ZERO)) } // 0xF0
+    fn bne_rel(&mut self, bus: &mut impl Bus) -> u8 { self.branch(bus, !self.flag(FLAG_ZERO)) } // 0xD0
+    fn bpl_rel(&mut self, bus: &mut impl Bus) -> u8 { self.branch(bus, !self.flag(FLAG_NEGATIVE)) } // 0x10
+    fn bmi_rel(&mut self, bus: &mut impl Bus) -> u8 { self.branch(bus, self.flag(FLAG_NEGATIVE)) } // 0x30
+    fn bvc_rel(&mut self, bus: &mut impl Bus) -> u8 { self.branch(bus, !self.flag(FLAG_OVERFLOW)) } // 0x50
+    fn bvs_rel(&mut self, bus: &mut impl Bus) -> u8 { self.branch(bus, self.flag(FLAG_OVERFLOW)) } //0x70
+
     // NES 6502 opcode length table/matcher
     fn opcode_len(opcode: u8) -> u8 {
         match opcode {
@@ -290,6 +323,14 @@ impl Cpu {
             0x00 => 1, // BRK imp
             0xEA => 1, // NOP
             0x38 => 1, // SEC imp 
+            0x90 => 2, // BCS rel
+            0xB0 => 2, // BCC rel
+            0xF0 => 2, // BEQ rel
+            0xD0 => 2, // BNE rel
+            0x10 => 2, // BPL rel
+            0x30 => 2, // BMI rel
+            0x50 => 2, // BVC rel
+            0x70 => 2, // BVS rel
             _ => 1, // fallback, would show the invalid/unknown opcode only not its parameters
         }
     }