From 2b16ed99405805c16260085f46c753792c1af32d Mon Sep 17 00:00:00 2001
From: aliaspider
Date: Thu, 30 Oct 2014 01:51:26 +0100
Subject: add safety to buffer reads to deal with negative offsets.

---
 libretro.c    | 38 ++++++++++++++++++++++++++++----------
 source/gfx.h  |  5 +++++
 source/tile.c |  4 ----
 3 files changed, 33 insertions(+), 14 deletions(-)

diff --git a/libretro.c b/libretro.c
index df44791..af29968 100644
--- a/libretro.c
+++ b/libretro.c
@@ -133,29 +133,47 @@ void S9xExtraUsage()
 void S9xDeinitDisplay(void)
 {
 #ifdef DS2_DMA
-   if (GFX.Screen) AlignedFree(GFX.Screen, PtrAdj.GFXScreen);
+   if (GFX.Screen_buffer) AlignedFree(GFX.Screen, PtrAdj.GFXScreen);
 #else
-   if (GFX.Screen) free(GFX.Screen);
+   if (GFX.Screen_buffer) free(GFX.Screen_buffer);
 #endif
-   if (GFX.SubScreen) free(GFX.SubScreen);
-   if (GFX.ZBuffer) free(GFX.ZBuffer);
-   if (GFX.SubZBuffer) free(GFX.SubZBuffer);
+   if (GFX.SubScreen_buffer) free(GFX.SubScreen_buffer);
+   if (GFX.ZBuffer_buffer) free(GFX.ZBuffer_buffer);
+   if (GFX.SubZBuffer_buffer) free(GFX.SubZBuffer_buffer);
+
+   GFX.Screen = NULL;
+   GFX.Screen_buffer = NULL;
+   GFX.SubScreen = NULL;
+   GFX.SubScreen_buffer = NULL;
+   GFX.ZBuffer = NULL;
+   GFX.ZBuffer_buffer = NULL;
+   GFX.SubZBuffer = NULL;
+   GFX.SubZBuffer_buffer = NULL;
+
 }
 
 void S9xInitDisplay(void)
 {
    int h = IMAGE_HEIGHT;
+   const int safety = 32;
 
    GFX.Pitch = IMAGE_WIDTH * 2;
 #ifdef DS2_DMA
-   GFX.Screen = (unsigned char*) AlignedMalloc(GFX.Pitch * h, 32,
+   GFX.Screen_buffer = (unsigned char*) AlignedMalloc(GFX.Pitch * h + safety, 32,
                 &PtrAdj.GFXScreen);
 #else
-   GFX.Screen = (unsigned char*) malloc(GFX.Pitch * h);
+   GFX.Screen_buffer = (unsigned char*) malloc(GFX.Pitch * h + safety);
 #endif
-   GFX.SubScreen = (unsigned char*) malloc(GFX.Pitch * h);
-   GFX.ZBuffer = (unsigned char*) malloc((GFX.Pitch >> 1) * h);
-   GFX.SubZBuffer = (unsigned char*) malloc((GFX.Pitch >> 1) * h);
+   GFX.SubScreen_buffer = (unsigned char*) malloc(GFX.Pitch * h + safety);
+   GFX.ZBuffer_buffer = (unsigned char*) malloc((GFX.Pitch >> 1) * h + safety);
+   GFX.SubZBuffer_buffer = (unsigned char*) malloc((GFX.Pitch >> 1) * h + safety);
+
+   GFX.Screen = GFX.Screen_buffer + safety;
+   GFX.SubScreen = GFX.SubScreen_buffer + safety;
+   GFX.ZBuffer = GFX.ZBuffer_buffer + safety;
+   GFX.SubZBuffer = GFX.SubZBuffer_buffer + safety;
+
+
    GFX.Delta = (GFX.SubScreen - GFX.Screen) >> 1;
 }
 
diff --git a/source/gfx.h b/source/gfx.h
index 55b31bf..18d74f8 100644
--- a/source/gfx.h
+++ b/source/gfx.h
@@ -114,6 +114,11 @@ void S9xSyncSpeed();
 struct SGFX
 {
    // Initialize these variables
+   uint8*  Screen_buffer;
+   uint8*  SubScreen_buffer;
+   uint8*  ZBuffer_buffer;
+   uint8*  SubZBuffer_buffer;
+
    uint8*  Screen;
    uint8*  SubScreen;
    uint8*  ZBuffer;
diff --git a/source/tile.c b/source/tile.c
index 2211421..31c065a 100644
--- a/source/tile.c
+++ b/source/tile.c
@@ -467,8 +467,6 @@ static void WRITE_4PIXELS16_ADD(int32 Offset, uint8* Pixels,
                                 uint16* ScreenColors)
 {
    uint8  Pixel, N;
-   if (Offset < 0)
-      Offset = 0;
 
    uint16* Screen = (uint16*) GFX.S + Offset;
    uint8*  Depth = GFX.ZBuffer + Offset;
@@ -499,8 +497,6 @@ static void WRITE_4PIXELS16_FLIPPED_ADD(int32 Offset, uint8* Pixels,
                                         uint16* ScreenColors)
 {
    uint8  Pixel, N;
-   if (Offset < 0)
-      Offset = 0;
 
    uint16* Screen = (uint16*) GFX.S + Offset;
    uint8*  Depth = GFX.ZBuffer + Offset;
-- 
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