encode: add convert_LTYPE_strings_area

for 256/512 byte conversions.
See GH #910

include/dwg.h

@@ -2531,7 +2531,7 @@ typedef struct _dwg_object_LTYPE
   Dwg_LTYPE_dash* dashes;
   BITCODE_RD dashes_r11[12];
   BITCODE_B has_strings_area; /* if some shape_flag & 4 (ODA bug) */
-  BITCODE_TF strings_area;
+  BITCODE_TF strings_area; /* 256 or 512 byte since r2007 */
   BITCODE_RC unknown_r11;
 } Dwg_Object_LTYPE;
 

src/common.h

@@ -666,6 +666,10 @@ void dwg_log_proxyflag (const int _loglevel, const int maxlevel,
                         const BITCODE_BS flag);
 void dwg_log_dataflags (const int _loglevel, const int maxlevel,
                         const BITCODE_RC flag);
+// in encode, but also in dwg.spec
+void
+dwg_convert_LTYPE_strings_area (const Dwg_Data *restrict dwg,
+                                Dwg_Object_LTYPE *restrict _obj) __nonnull_all;
 
 // in the public API, but we don't use that for most internal modules
 #if !defined _DWG_API_H_ && !defined _DWG_API_C && !defined DYNAPI_TEST_C     \

src/dwg.c

@@ -3524,7 +3524,7 @@ EXPORT int dwg_supports_eed (const Dwg_Data *dwg)
 
 EXPORT int
 dwg_supports_obj (const Dwg_Data *restrict dwg,
-                     const Dwg_Object *restrict obj)
+                  const Dwg_Object *restrict obj)
 {
   const Dwg_Object_Type type = obj->fixedtype;
   Dwg_Version_Type ver;

src/dwg.spec

@@ -3971,6 +3971,11 @@ DWG_TABLE (LTYPE)
     END_REPEAT (dashes);
 
     UNTIL (R_2004) {
+      // downconvert from 512
+      ENCODER {
+        if (dwg->header.from_version > R_2004)
+          dwg_convert_LTYPE_strings_area (dwg, _obj);
+      }
       FIELD_BINARY (strings_area, 256, 0);
       DECODER {
         unsigned int dash_i = 0;
@@ -3994,6 +3999,11 @@ DWG_TABLE (LTYPE)
     }
     LATER_VERSIONS {
       if (FIELD_VALUE (has_strings_area)) {
+        // upconvert from 256
+        ENCODER {
+          if (dwg->header.from_version <= R_2004)
+            dwg_convert_LTYPE_strings_area (dwg, _obj);
+        }
         FIELD_BINARY (strings_area, 512, 0);
         DECODER {
           BITCODE_RS dash_i = 0;

src/encode.c

@@ -7403,4 +7403,35 @@ downconvert_DIMSTYLE (Bit_Chain *restrict dat, Dwg_Object *restrict obj)
     }
 }
 
+// up or downconvert from/to 256/512 bytes
+void
+dwg_convert_LTYPE_strings_area (const Dwg_Data *restrict dwg,
+                                Dwg_Object_LTYPE *restrict _obj)
+{
+  if (dwg->header.from_version <= R_2004 && dwg->header.version > R_2004)
+    {
+      // upconvert to 512
+      BITCODE_TF old = _obj->strings_area;
+      _obj->strings_area = calloc (1, 512);
+      if (!_obj->strings_area || !old)
+        return;
+      for (int i = 0; i < 256; i++)
+        {
+          _obj->strings_area[i * 2] = old[i];
+        }
+    }
+  else if (dwg->header.from_version > R_2004 && dwg->header.version <= R_2004)
+    {
+      // downconvert to 256
+      BITCODE_TF old = _obj->strings_area;
+      _obj->strings_area = calloc (1, 256);
+      if (!_obj->strings_area || !old)
+        return;
+      for (int i = 0; i < 256; i++)
+        {
+          _obj->strings_area[i] = old[i * 2];
+        }
+    }
+}
+
 #undef IS_ENCODER

src/encode.h

@@ -54,4 +54,5 @@ bool dwg_encode_unknown_bits (Bit_Chain *restrict dat,
                               Dwg_Object *restrict obj);
 void downconvert_TABLESTYLE (Dwg_Object *restrict obj);
 
+
 #endif