instruction decoding

src/memory.c

@@ -22,3 +22,43 @@ inline uint16_t memoryLoadWord(Memory* m, uint32_t address) {
 inline void memorySaveWord(Memory* m, uint32_t address, uint16_t value) {
     ((uint16_t*)m->data)[address] = value;
 }
+
+Instruction decodeInstruction(Memory* m, uint32_t* pc) {
+    SerializedInst serialized = m->data[*pc];
+    Instruction outputInst = {};
+
+    uint8_t opcode = serialized & 0b0000000000001111; // get four lowest bits for the opcode
+    outputInst.opcode = opcode;
+
+    const OperandType* opTypes = INSTRUCTION_OPERAND_TYPES[opcode];
+
+    uint8_t offset = 0;
+    for (uint8_t i = 0; i < 3; i++) {
+        switch (opTypes[i]) {
+            case OP_REG: {
+                // get the data at the current offset, and grab the 4 bits that are there with a bitwise
+                // "and" operator
+                outputInst.operands[offset] = (serialized >> (4 * (offset + 1))) & 0b0000000000001111;
+                offset++;
+                break;
+            }
+
+            case OP_IMM16: { // the immediate 16 takes up the space where the next instruction would be
+                uint16_t nextDataOver = m->data[++*pc];
+                outputInst.immediate = nextDataOver;
+                break;
+            }
+
+            case OP_NONE: {
+                break;
+            }
+        }
+    }
+
+    return outputInst;
+}
+
+void freeMemory(Memory* m) {
+    free(m->data);
+    free(m);
+}