Changes between Version 20 and Version 21 of PIL

Timestamp:

10/16/24 15:04:14 (19 months ago)

Author:

siegel

Comment:

--

PIL

@@ -316 +316 @@
 == Objects
 
-The function
 - `$obj $empty_obj($int size);`
-returns the empty object spanning `size` bytes.  Only values of a sized type can be written to an object.
+ * this function returns the empty object spanning `size` bytes.
+   Only values of a sized type can be written to an object.
+- `void* $obj_base($obj* optr);`
+ * returns a pointer to byte 0 of the object.  That pointer can be cast to different
+   pointer types in order to access the object.
 
 An object is modified through a pointer into the object, for example:
@@ -325 +328 @@
 typedef $size(8) $real double;
 $obj o1 = $empty_obj(1000);
-double* dp = (double*)&o1;  // points to byte 0
+double* dp = (double*)$obj_base(&o1);  // points to byte 0
 *dp = 3.14;
 *(dp+7) = 2.718;
-int* ip = (int*)&o1;
+int* ip = (int*)dp;
 *(ip+2) = 17;
 }}}
-The operations above place the double value 3.14 in o1 at positions 0..7, the double value 2.718 at positions 28..35, and the integer value 17 at positions 8..11.
+The operations above place the double value 3.14 in `o1` at positions 0..7, the double value 2.718 at positions 28..35, and the integer value 17 at positions 8..11.
 
 If a write to an object overlaps the interval of an existing value, the old value is removed.
@@ -343 +346 @@
 * how to deal with "undefined" values?
 * can there be nondeterministic expressions, i.e., expressions that evaluate to a set of values instead of one value?
+* can there be nondeterministic statements, i.e., statements which result in multiple transitions
 * how to implement C's malloc?
-* what to return when something is wrong, e.g., $map_get$ when the specified key is not in the map (default value of type?)
-
-Ideas on malloc:
-
-Union of all types occurring in program:
-{{{
-typedef union {
-  T1 t1;
-  T2 t2;
-  ...
-} BigUnion;
-}}}
-
-A call to malloc returns a memory block:
-  - size (in bytes) (int)
-  - num_elements (int)
-  - sequence of tuples:
-    - offset (int)
-    - size (int)
-    - value (type `BigUnion`)
+