Revert binary database block position encoding

This reverts commits a2003b0d553c7223a61c75e5dad79ea68e058ba2 and 54ffe2e5de9ce44129f84f4748743f893b75fda7.

These weren't correct.  Add a black magic warning instead.

diff --git a/src/database.cpp b/src/database.cpp
index 15579a7f094955bee32292f11969578c2e428d91..26f6992fcb47e7e84b5fad70707857fcaa1cd857 100644 (file)
--- a/src/database.cpp
+++ b/src/database.cpp
@@ -20,6 +20,14 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 #include "database.h"
 #include "irrlichttypes.h"
 
+
+/****************
+ * Black magic! *
+ ****************
+ * The position hashing is very messed up.
+ * It's a lot more complicated than it looks.
+ */
+
 static inline s16 unsigned_to_signed(u16 i, u16 max_positive)
 {
        if (i < max_positive) {
@@ -30,19 +38,32 @@ static inline s16 unsigned_to_signed(u16 i, u16 max_positive)
 }
 
 
+// Modulo of a negative number does not work consistently in C
+static inline s64 pythonmodulo(s64 i, s16 mod)
+{
+       if (i >= 0) {
+               return i % mod;
+       }
+       return mod - ((-i) % mod);
+}
+
+
 s64 Database::getBlockAsInteger(const v3s16 pos) const
 {
-       return (((u64) pos.Z) << 24) +
-               (((u64) pos.Y) << 12) +
-               ((u64) pos.X);
+       return (u64) pos.Z * 0x1000000 +
+               (u64) pos.Y * 0x1000 +
+               (u64) pos.X;
 }
 
-v3s16 Database::getIntegerAsBlock(const s64 i) const
+
+v3s16 Database::getIntegerAsBlock(s64 i) const
 {
-        v3s16 pos;
-        pos.Z = unsigned_to_signed((i >> 24) & 0xFFF, 0x1000 / 2);
-        pos.Y = unsigned_to_signed((i >> 12) & 0xFFF, 0x1000 / 2);
-        pos.X = unsigned_to_signed((i      ) & 0xFFF, 0x1000 / 2);
-        return pos;
+       v3s16 pos;
+       pos.X = unsigned_to_signed(pythonmodulo(i, 4096), 2048);
+       i = (i - pos.X) / 4096;
+       pos.Y = unsigned_to_signed(pythonmodulo(i, 4096), 2048);
+       i = (i - pos.Y) / 4096;
+       pos.Z = unsigned_to_signed(pythonmodulo(i, 4096), 2048);
+       return pos;
 }
 

diff --git a/src/database.h b/src/database.h
index a8686137949ba251a1a8075c55e9f6819305f93a..f009877d244cac6a780bf44f779f5359905b1772 100644 (file)
--- a/src/database.h
+++ b/src/database.h
@@ -35,7 +35,7 @@ public:
        virtual void saveBlock(MapBlock *block)=0;
        virtual MapBlock* loadBlock(v3s16 blockpos)=0;
        s64 getBlockAsInteger(const v3s16 pos) const;
-       v3s16 getIntegerAsBlock(const s64 i) const;
+       v3s16 getIntegerAsBlock(s64 i) const;
        virtual void listAllLoadableBlocks(std::list<v3s16> &dst)=0;
        virtual int Initialized(void)=0;
        virtual ~Database() {};