From 6c388020b0de898bc5f9338a883261cc8e181b17 Mon Sep 17 00:00:00 2001
From: Thomas Bernard <miniupnp@free.fr>
Date: Fri, 6 Dec 2019 00:22:25 +0100
Subject: [PATCH] improve debug output of Load_SCR()

---
 src/gfx2mem.c         | 11 +++++++++++
 src/gfx2mem.h         |  3 +++
 src/miscfileformats.c | 31 ++++++++++++++++++++-----------
 3 files changed, 34 insertions(+), 11 deletions(-)

diff --git a/src/gfx2mem.c b/src/gfx2mem.c
index 1156c586..a8d3bad1 100644
--- a/src/gfx2mem.c
+++ b/src/gfx2mem.c
@@ -30,3 +30,14 @@ void * GFX2_malloc_and_log(size_t size, const char * file, unsigned line)
              file, line, (unsigned long)size);
   return p;
 }
+
+int GFX2_is_mem_filled_with(const void * p, unsigned char b, size_t len)
+{
+  const unsigned char * pp = (const unsigned char *)p;
+  while (len-- > 0)
+  {
+    if (*pp++ != b)
+      return 0;
+  }
+  return 1;
+}
diff --git a/src/gfx2mem.h b/src/gfx2mem.h
index 537b559f..6ff1bca9 100644
--- a/src/gfx2mem.h
+++ b/src/gfx2mem.h
@@ -27,4 +27,7 @@ void * GFX2_malloc_and_log(size_t size, const char * file, unsigned line);
 /// malloc() memory and log in case of error
 #define GFX2_malloc(size) GFX2_malloc_and_log((size), __FILE__, __LINE__)
 
+/// checks if a memory zone is filled with the same byte value
+int GFX2_is_mem_filled_with(const void * p, unsigned char b, size_t len);
+
 #endif
diff --git a/src/miscfileformats.c b/src/miscfileformats.c
index 32b5a415..98ebf781 100644
--- a/src/miscfileformats.c
+++ b/src/miscfileformats.c
@@ -4662,8 +4662,6 @@ void Load_SCR(T_IO_Context * context)
           0x54, 0x44, 0x55, 0x5c, 0x58, 0x5d, 0x4c, 0x45, 0x4d,
           0x56, 0x46, 0x57, 0x5e, 0x40, 0x5f, 0x4e, 0x47, 0x4f,
           0x52, 0x42, 0x53, 0x5a, 0x59, 0x5b, 0x4a, 0x43, 0x4b };
-        GFX2_LogHexDump(GFX2_DEBUG, "", cpc_ram, 0x800, 0x100);
-        GFX2_LogHexDump(GFX2_DEBUG, "", cpc_ram, 0x8000, 0x100);
         mode = cpc_ram[0x800];
         for (j = 0; j < 16; j++)
           pal_data[12*j] = CPC_Firmware_Colors[cpc_ram[0x801 + j]];
@@ -4751,16 +4749,27 @@ void Load_SCR(T_IO_Context * context)
     {
       addr = display_start + 0x800 * y;
       if (y > 0 && (display_start & 0x7ff))
-        GFX2_LogHexDump(GFX2_DEBUG, "SCR1 ", cpc_ram,
-                        addr & 0xf800, display_start & 0x7ff);
+      {
+        if (!GFX2_is_mem_filled_with(cpc_ram + (addr & 0xf800), 0, display_start & 0x7ff))
+          GFX2_LogHexDump(GFX2_DEBUG, "SCR1 ", cpc_ram,
+                          addr & 0xf800, display_start & 0x7ff);
+      }
       addr += (height >> 3) * columns;
-      if ((height >> 3) * columns + (display_start & 0x7ff) <= 0x800)
-        GFX2_LogHexDump(GFX2_DEBUG, "SCR2 ", cpc_ram,
-                        addr, 0x800 - ((height >> 3) * columns + (display_start & 0x7ff)));
-       else
-         GFX2_LogHexDump(GFX2_DEBUG, "SCR2 ", cpc_ram,
-                        addr + 0x4000, 0x1000 - ((height >> 3) * columns + (display_start & 0x7ff)));
-
+      block_length = (height >> 3) * columns + (display_start & 0x7ff);
+      if (block_length <= 0x800)
+      {
+        block_length = 0x800 - block_length;
+        if (!GFX2_is_mem_filled_with(cpc_ram + addr, 0, block_length))
+          GFX2_LogHexDump(GFX2_DEBUG, "SCR2 ", cpc_ram,
+                          addr, block_length);
+      }
+      else
+      {
+        block_length = 0x1000 - block_length;
+        if (!GFX2_is_mem_filled_with(cpc_ram + addr + 0x4000, 0, block_length))
+          GFX2_LogHexDump(GFX2_DEBUG, "SCR2 ", cpc_ram,
+                          addr + 0x4000, block_length);
+      }
     }
     //for (j = 0; j < i; j += 2048)
     //  GFX2_LogHexDump(GFX2_DEBUG, "SCR ", cpc_ram, load_address + j + 2000, 48);