Part01-01: Project setup and basic decoding

.gitignore

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+/decode

Makefile

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+CFLAGS=-g -std=c2x -fsanitize=address -fno-omit-frame-pointer -Wall -Wextra -pedantic -O0
+CC=gcc
+
+.PHONY: build clean run all
+
+all: decode
+
+decode: decode.c
+	$(CC) $(CFLAGS) $< -o $@
+
+run: all
+	./decode
+
+clean:
+	rm -vf *.so *.o decode

README.org

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+#+OPTIONS: toc:nil
+
+* 8086 CPU Emulator
+Following along with [[https://www.computerenhance.com/p/table-of-contents][Performance Aware by Computer Enhance]]
+* License
+This project is licensed under the terms of the MIT license. For more
+information, see the included LICENSE file. However, some of this is related to
+a paid course so maybe pay for the course if you want to use these files?

asm_files/01-01-37.asm

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+; ========================================================================
+; LISTING 37
+; ========================================================================
+
+bits 16
+
+mov bx, cx                      ; mov 001, 011

decode.c

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+#include <stdio.h>
+#include <stdlib.h>
+
+#define ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0]))
+
+enum Instruction
+{
+    INST_MOV = 0b10001000
+};
+
+enum Register
+{
+    REG_AL_AX = 0b000,
+    REG_CL_CX = 0b001,
+    REG_DL_DX = 0b010,
+    REG_BL_BX = 0b011,
+    REG_AH_SP = 0b100,
+    REG_CH_BP = 0b101,
+    REG_DH_SI = 0b110,
+    REG_BH_DI = 0b111,
+};
+
+#define REG_AX "ax"
+#define REG_CX "cx"
+#define REG_BX "bx"
+
+enum Mode
+{
+    MODE_MEM_NOD = 0b00,
+    MODE_MEM_08D = 0b01,
+    MODE_MEM_16D = 0b10,
+    MODE_REGMODE = 0b11,
+};
+
+int main(int argc, char **argv)
+{
+    if (argc < 2)
+    {
+        printf("Usage: Please provide assembled instructions as input\n");
+        exit(0);
+    }
+    unsigned char buf[256];
+    FILE *f = fopen(argv[1], "r");
+    if (!f)
+    {
+        perror("fopen\n");
+        return EXIT_FAILURE;
+    }
+    size_t bytes_read = fread(buf, sizeof(*buf), ARRAY_SIZE(buf), f);
+
+    printf("; Decoded 8086 Assembly Instructions\n\n");
+    printf("bits 16\n\n");
+    for (int i = 0; i < (int)bytes_read / 2; i += 2)
+    {
+        char byte = buf[i];
+        switch (byte & 0b11111100)
+        {
+        case INST_MOV:
+            char high_byte = buf[i+1];
+            // char w = byte & 0b00000001;
+            // char d = byte & 0b00000010;
+            char mod = (high_byte & 0b11000000) >> 6;
+            char reg = (high_byte & 0b00111000) >> 3;
+            char r_m = (high_byte & 0b00000111);
+            printf("mov ");
+            if (mod == MODE_REGMODE)
+            {
+                char *dest_reg_name = NULL;
+                switch (r_m)
+                {
+                case REG_CL_CX:
+                    dest_reg_name = REG_CX;
+                    break;
+                case REG_BL_BX:
+                    dest_reg_name = REG_BX;
+                    break;
+                }
+                printf("%s, ", dest_reg_name);
+                
+                char *src_reg_name = NULL;
+                switch (reg)
+                {
+                case REG_CL_CX:
+                    src_reg_name = REG_CX;
+                    break;
+                case REG_BL_BX:
+                    src_reg_name = REG_BX;
+                    break;
+                }
+                printf("%s", src_reg_name);
+            }
+            break;
+        default:
+            perror("Unrecognized Instruction\n");
+        }
+    }
+    printf("\n");
+}