From 274760746e67d7939924cec2bd6ef55057f2c036 Mon Sep 17 00:00:00 2001
From: Lior Halphon <LIJI32@gmail.com>
Date: Fri, 7 Jun 2019 19:18:07 +0300
Subject: [PATCH] Fix #165

---
 Core/gb.c         |  6 +++---
 Core/gb.h         |  2 +-
 Core/save_state.c | 39 ++++++++++++++++++++++++++++++++++-----
 3 files changed, 38 insertions(+), 9 deletions(-)

diff --git a/Core/gb.c b/Core/gb.c
index bad1910..2712da9 100644
--- a/Core/gb.c
+++ b/Core/gb.c
@@ -95,7 +95,7 @@ void GB_init(GB_gameboy_t *gb, GB_model_t model)
     memset(gb, 0, sizeof(*gb));
     gb->model = model;
     if (GB_is_cgb(gb)) {
-        gb->ram = malloc(gb->ram_size = 0x2000 * 8);
+        gb->ram = malloc(gb->ram_size = 0x1000 * 8);
         gb->vram = malloc(gb->vram_size = 0x2000 * 2);
     }
     else {
@@ -632,7 +632,7 @@ void GB_reset(GB_gameboy_t *gb)
     gb->io_registers[GB_IO_JOYP] = 0xF;
     gb->mbc_ram_size = mbc_ram_size;
     if (GB_is_cgb(gb)) {
-        gb->ram_size = 0x2000 * 8;
+        gb->ram_size = 0x1000 * 8;
         gb->vram_size = 0x2000 * 2;
         memset(gb->vram, 0, gb->vram_size);
         gb->cgb_mode = true;
@@ -703,7 +703,7 @@ void GB_switch_model_and_reset(GB_gameboy_t *gb, GB_model_t model)
 {
     gb->model = model;
     if (GB_is_cgb(gb)) {
-        gb->ram = realloc(gb->ram, gb->ram_size = 0x2000 * 8);
+        gb->ram = realloc(gb->ram, gb->ram_size = 0x1000 * 8);
         gb->vram = realloc(gb->vram, gb->vram_size = 0x2000 * 2);
     }
     else {
diff --git a/Core/gb.h b/Core/gb.h
index b798a04..5385710 100644
--- a/Core/gb.h
+++ b/Core/gb.h
@@ -333,6 +333,7 @@ struct GB_gameboy_internal_s {
         bool infrared_input;
         GB_printer_t printer;
         uint8_t extra_oam[0xff00 - 0xfea0];
+        uint32_t ram_size; // Different between CGB and DMG
     );
 
     /* DMA and HDMA */
@@ -593,7 +594,6 @@ struct GB_gameboy_internal_s {
         bool turbo;
         bool turbo_dont_skip;
         bool disable_rendering;
-        uint32_t ram_size; // Different between CGB and DMG
         uint8_t boot_rom[0x900];
         bool vblank_just_occured; // For slow operations involving syscalls; these should only run once per vblank
         uint8_t cycles_since_run; // How many cycles have passed since the last call to GB_run(), in 8MHz units
diff --git a/Core/save_state.c b/Core/save_state.c
index 26c9b52..1cd3458 100644
--- a/Core/save_state.c
+++ b/Core/save_state.c
@@ -156,11 +156,6 @@ static bool verify_state_compatibility(GB_gameboy_t *gb, GB_gameboy_t *save)
         return false;
     }
     
-    if (gb->ram_size != save->ram_size) {
-        GB_log(gb, "The save state has non-matching RAM size. Try changing the emulated model.\n");
-        return false;
-    }
-    
     if (gb->vram_size != save->vram_size) {
         GB_log(gb, "The save state has non-matching VRAM size. Try changing the emulated model.\n");
         return false;
@@ -171,6 +166,17 @@ static bool verify_state_compatibility(GB_gameboy_t *gb, GB_gameboy_t *save)
         return false;
     }
     
+    if (gb->ram_size != save->ram_size) {
+        if (gb->ram_size == 0x1000 * 8 && save->ram_size == 0x2000 * 8) {
+            /* A bug in versions prior to 0.12 made CGB instances allocate twice the ammount of RAM.
+               Ignore this issue to retain compatibility with older, 0.11, save states. */
+        }
+        else {
+            GB_log(gb, "The save state has non-matching RAM size. Try changing the emulated model.\n");
+            return false;
+        }
+    }
+    
     return true;
 }
 
@@ -182,6 +188,8 @@ int GB_load_state(GB_gameboy_t *gb, const char *path)
     
     /* Every unread value should be kept the same. */
     memcpy(&save, gb, sizeof(save));
+    /* ...Except ram size, we use it to detect old saves with incorrect ram sizes */
+    save.ram_size = 0;
     
     FILE *f = fopen(path, "rb");
     if (!f) {
@@ -199,6 +207,17 @@ int GB_load_state(GB_gameboy_t *gb, const char *path)
     if (!READ_SECTION(&save, f, rtc       )) goto error;
     if (!READ_SECTION(&save, f, video     )) goto error;
     
+    if (save.ram_size == 0) {
+        /* Save doesn't have ram size specified, it's a pre 0.12 save state with potentially
+           incorrect RAM amount if it's a CGB instance */
+        if (GB_is_cgb(&save)) {
+            save.ram_size = 0x2000 * 8; // Incorrect RAM size
+        }
+        else {
+            save.ram_size = gb->ram_size;
+        }
+    }
+    
     if (!verify_state_compatibility(gb, &save)) {
         errno = -1;
         goto error;
@@ -218,13 +237,19 @@ int GB_load_state(GB_gameboy_t *gb, const char *path)
         fclose(f);
         return EIO;
     }
+
+    /* Fix for 0.11 save states that allocate twice the amount of RAM in CGB instances */
+    fseek(f, save.ram_size - gb->ram_size, SEEK_CUR);
     
     if (fread(gb->vram, 1, gb->vram_size, f) != gb->vram_size) {
         fclose(f);
         return EIO;
     }
     
+    size_t orig_ram_size = gb->ram_size;
     memcpy(gb, &save, sizeof(save));
+    gb->ram_size = orig_ram_size;
+
     errno = 0;
     
     if (gb->cartridge_type->has_rumble && gb->rumble_callback) {
@@ -324,6 +349,10 @@ int GB_load_state_from_buffer(GB_gameboy_t *gb, const uint8_t *buffer, size_t le
         return -1;
     }
     
+    /* Fix for 0.11 save states that allocate twice the amount of RAM in CGB instances */
+    buffer += save.ram_size - gb->ram_size;
+    length -= save.ram_size - gb->ram_size;
+    
     memcpy(gb, &save, sizeof(save));
     
     if (gb->cartridge_type->has_rumble && gb->rumble_callback) {