From f3f15de8cc8c7d39fe47efe9385a7d3909a82e80 Mon Sep 17 00:00:00 2001
From: Sam M W <you@example.com>
Date: Mon, 3 Apr 2023 05:47:29 +0100
Subject: [PATCH] remove memory.get_slice

real hardware won't have the ability to dive in and grab a slice from
memory
---
 src/cpu.rs         | 16 ++++++++++++++--
 src/instruction.rs | 19 +++++++++++++------
 src/memory.rs      |  7 -------
 3 files changed, 27 insertions(+), 15 deletions(-)

diff --git a/src/cpu.rs b/src/cpu.rs
index c4208bc..6de3598 100644
--- a/src/cpu.rs
+++ b/src/cpu.rs
@@ -63,8 +63,20 @@ impl CPU {
 
                 let data_start = self.registers.program_counter.wrapping_add(1);
 
-                let slice = self.memory.get_slice(data_start, extra_bytes);
-                let am_out = am.process(self, slice);
+                let slice = if extra_bytes == 0 {
+                    [0, 0]
+                } else if extra_bytes == 1 {
+                    [self.memory.get_byte(data_start), 0]
+                } else if extra_bytes == 2 {
+                    [
+                        self.memory.get_byte(data_start),
+                        self.memory.get_byte(data_start.wrapping_add(1)),
+                    ]
+                } else {
+                    panic!()
+                };
+
+                let am_out = am.process(self, &slice[..extra_bytes as usize]);
 
                 // Increment program counter
                 self.registers.program_counter =
diff --git a/src/instruction.rs b/src/instruction.rs
index 7ba88d1..b755d05 100644
--- a/src/instruction.rs
+++ b/src/instruction.rs
@@ -26,6 +26,7 @@
 // POSSIBILITY OF SUCH DAMAGE.
 
 use crate::cpu::CPU;
+use crate::memory::Memory;
 
 // Abbreviations
 //
@@ -171,6 +172,12 @@ impl AddressingMode {
 
         let memory = &cpu.memory;
 
+        fn read_address(mem: &Memory, addr: u16) -> [u8; 2] {
+            let lo = mem.get_byte(addr);
+            let hi = mem.get_byte(addr.wrapping_add(1));
+            [lo, hi]
+        }
+
         match self {
             AddressingMode::Accumulator | AddressingMode::Implied => {
                 // Always the same -- no input
@@ -227,8 +234,8 @@ impl AddressingMode {
                 // Use [u8, ..2] from instruction as an address. Interpret the
                 // two bytes starting at that address as an address.
                 // (Output: a 16-bit address)
-                let slice = memory.get_slice(arr_to_addr(arr), 2);
-                OpInput::UseAddress(arr_to_addr(slice))
+                let slice = read_address(memory, arr_to_addr(arr));
+                OpInput::UseAddress(arr_to_addr(&slice))
             }
             AddressingMode::IndexedIndirectX => {
                 // Use [u8, ..1] from instruction
@@ -236,8 +243,8 @@ impl AddressingMode {
                 // This is where the absolute (16-bit) target address is stored.
                 // (Output: a 16-bit address)
                 let start = arr[0].wrapping_add(x);
-                let slice = memory.get_slice(u16::from(start), 2);
-                OpInput::UseAddress(arr_to_addr(slice))
+                let slice = read_address(memory, u16::from(start));
+                OpInput::UseAddress(arr_to_addr(&slice))
             }
             AddressingMode::IndirectIndexedY => {
                 // Use [u8, ..1] from instruction
@@ -245,8 +252,8 @@ impl AddressingMode {
                 // Add Y register to this address to get the final address
                 // (Output: a 16-bit address)
                 let start = arr[0];
-                let slice = memory.get_slice(u16::from(start), 2);
-                OpInput::UseAddress(arr_to_addr(slice).wrapping_add(xextend(y)))
+                let slice = read_address(memory, u16::from(start));
+                OpInput::UseAddress(arr_to_addr(&slice).wrapping_add(xextend(y)))
             }
         }
     }
diff --git a/src/memory.rs b/src/memory.rs
index 4428978..c4f9535 100644
--- a/src/memory.rs
+++ b/src/memory.rs
@@ -69,13 +69,6 @@ impl Memory {
         self.bytes[address as usize]
     }
 
-    pub fn get_slice(&self, start: u16, diff: u16) -> &[u8] {
-        let orig: usize = start.into();
-        let end = orig + diff as usize;
-
-        &self.bytes[orig..end]
-    }
-
     // Sets the byte at the given address to the given value and returns the
     // previous value at the address.
     pub fn set_byte(&mut self, address: u16, value: u8) -> u8 {