From 332216b193e9bc0d59c4ce906139096587545a1c Mon Sep 17 00:00:00 2001
From: Ben Kurtovic <ben.kurtovic@gmail.com>
Date: Mon, 23 Mar 2015 21:11:09 -0400
Subject: [PATCH] Work on parsing headers.

---
 src/logging.h |  3 +++
 src/rom.c     | 80 ++++++++++++++++++++++++++++++++++++++++++++++++++++++-----
 src/rom.h     |  9 ++++---
 3 files changed, 82 insertions(+), 10 deletions(-)

diff --git a/src/logging.h b/src/logging.h
index f5df66e..f95398b 100644
--- a/src/logging.h
+++ b/src/logging.h
@@ -30,6 +30,9 @@
 #ifdef DEBUG_MODE
 #define DEBUG(...)       LOG_MSG("[DEBUG]", {},            {},                 __VA_ARGS__)
 #define DEBUG_ERRNO(...) LOG_MSG("[DEBUG]", PRINT_ERRNO(), {},                 __VA_ARGS__)
+#else
+#define DEBUG(...)       {}
+#define DEBUG_ERRNO(...) {}
 #endif
 
 #define OUT_OF_MEMORY() FATAL("couldn't allocate enough memory")
diff --git a/src/rom.c b/src/rom.c
index 2113200..7686ea9 100644
--- a/src/rom.c
+++ b/src/rom.c
@@ -1,6 +1,7 @@
 /* Copyright (C) 2014-2015 Ben Kurtovic <ben.kurtovic@gmail.com>
    Released under the terms of the MIT License. See LICENSE for details. */
 
+#include <ctype.h>
 #include <errno.h>
 #include <stdbool.h>
 #include <stdio.h>
@@ -11,17 +12,76 @@
 #include "rom.h"
 #include "logging.h"
 
+#define NUM_LOCATIONS 3
+#define MAGIC_LEN 8
+#define HEADER_SIZE 16
+
+static size_t header_locations[NUM_LOCATIONS] = {0x7ff0, 0x1ff0, 0x3ff0};
+static const char header_magic[MAGIC_LEN + 1] = "TMR SEGA";
+
 /*
     Return whether or not the given ROM image size is valid.
 */
 static bool validate_size(off_t size)
 {
+    if (size & (size - 1))
+        return false;  // Ensure size is a power of two
+
     off_t kbytes = size >> 10;
-    if (kbytes << 10 != size)
-        return false;
-    if (kbytes < 8 || kbytes > 1024)
-        return false;
-    return !(kbytes & (kbytes - 1));
+    return kbytes >= 8 && kbytes <= 1024;
+}
+
+#ifdef DEBUG_MODE
+/*
+    DEBUG FUNCTION: Print out the header to stdout.
+*/
+static void print_header(const char *header)
+{
+    char header_hex[3 * HEADER_SIZE], header_chr[3 * HEADER_SIZE];
+
+    for (int i = 0; i < HEADER_SIZE; i++) {
+        snprintf(&header_hex[3 * i], 3, "%02x", header[i]);
+        if (isprint(header[i]))
+            snprintf(&header_chr[3 * i], 3, "%2c", header[i]);
+        else {
+            header_chr[3 * i]     = ' ';
+            header_chr[3 * i + 1] = '?';
+        }
+        header_hex[3 * i + 2] = header_chr[3 * i + 2] = ' ';
+    }
+    header_hex[3 * HEADER_SIZE - 1] = header_chr[3 * HEADER_SIZE - 1] = '\0';
+    DEBUG("- header dump (hex): %s", header_hex)
+    DEBUG("- header dump (chr): %s", header_chr)
+}
+#endif
+
+/*
+    Read a ROM image's header, and return whether or not it is valid.
+*/
+static bool read_header(ROM *rom)
+{
+    size_t location, i;
+    const char *header;
+
+    DEBUG("- looking for header:")
+    for (i = 0; i < NUM_LOCATIONS; i++) {
+        location = header_locations[i];
+        DEBUG("  - trying location 0x%zx:", location)
+        header = &rom->data[location];
+        if (memcmp(header, header_magic, MAGIC_LEN)) {
+            DEBUG("    - magic not present")
+        }
+        else {
+            DEBUG("    - magic found")
+#ifdef DEBUG_MODE
+            print_header(header);
+#endif
+            // TODO: parse header
+            return true;
+        }
+    }
+    DEBUG("  - could not find header")
+    return false;
 }
 
 /*
@@ -61,8 +121,10 @@ const char* rom_open(ROM **rom_ptr, const char *path)
     if (!(rom->name = malloc(sizeof(char) * (strlen(path) + 1))))
         OUT_OF_MEMORY()
     strcpy(rom->name, path);
+    DEBUG("Loading ROM %s:", rom->name)
 
     // Set rom->size:
+    DEBUG("- size: %lld", st.st_size)
     if (!validate_size(st.st_size)) {
         rom_close(rom);
         fclose(fp);
@@ -78,8 +140,14 @@ const char* rom_open(ROM **rom_ptr, const char *path)
         fclose(fp);
         return rom_err_badread;
     }
-
     fclose(fp);
+
+    // Parse the header:
+    if (!read_header(rom)) {
+        rom_close(rom);
+        return rom_err_badheader;
+    }
+
     *rom_ptr = rom;
     return NULL;
 }
diff --git a/src/rom.h b/src/rom.h
index 3b3333f..efb7269 100644
--- a/src/rom.h
+++ b/src/rom.h
@@ -5,10 +5,11 @@
 
 /* Error strings */
 
-static const char* rom_err_isdir   = "Is a directory";
-static const char* rom_err_notfile = "Is not a regular file";
-static const char* rom_err_badsize = "Invalid size";
-static const char* rom_err_badread = "Couldn't read the entire file";
+static const char* rom_err_isdir     = "Is a directory";
+static const char* rom_err_notfile   = "Is not a regular file";
+static const char* rom_err_badsize   = "Invalid size";
+static const char* rom_err_badread   = "Couldn't read the entire file";
+static const char* rom_err_badheader = "Invalid header";
 
 /* Structs */