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diff --git a/gs/src/isdata.h b/gs/src/isdata.h
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+/* Copyright (C) 1992, 1995, 1997, 1998, 1999 Aladdin Enterprises.  All rights reserved.
+
+   This file is part of Aladdin Ghostscript.
+
+   Aladdin Ghostscript is distributed with NO WARRANTY OF ANY KIND.  No author
+   or distributor accepts any responsibility for the consequences of using it,
+   or for whether it serves any particular purpose or works at all, unless he
+   or she says so in writing.  Refer to the Aladdin Ghostscript Free Public
+   License (the "License") for full details.
+
+   Every copy of Aladdin Ghostscript must include a copy of the License,
+   normally in a plain ASCII text file named PUBLIC.  The License grants you
+   the right to copy, modify and redistribute Aladdin Ghostscript, but only
+   under certain conditions described in the License.  Among other things, the
+   License requires that the copyright notice and this notice be preserved on
+   all copies.
+ */
+
+
+/* Structure for expandable stacks of refs */
+/* Requires iref.h */
+
+#ifndef isdata_INCLUDED
+#  define isdata_INCLUDED
+
+/*
+ * In order to detect under- and overflow with minimum overhead, we put
+ * guard elements at the top and bottom of each stack block (see idsdata.h,
+ * iesdata.h, and iosdata.h for details of the individual stacks).  Note that
+ * the 'current' and 'next' arrays include the guard elements.  See
+ * istack.h for the details of stack blocks.
+ */
+
+/*
+ * The garbage collector requires that the entire contents of every block
+ * be 'clean', i.e., contain legitimate refs; we also need to ensure that
+ * at GC time, pointers in unused areas of a block will not be followed
+ * (since they may be dangling).  We ensure this as follows:
+ *      - When allocating a new block, we set the entire body to nulls.
+ *      This is necessary because the block may be freed before the next GC,
+ *      and the GC must be able to scan (parse) refs even if they are free.
+ *      - When adding a new block to the top of the stack, we set to nulls
+ *      the unused area of the new next-to-top blocks.
+ *      - At the beginning of garbage collection, we set to nulls the unused
+ *      elements of the top block.
+ */
+
+/*
+ * Define pointers into stacks.  Formerly, these were short (unsegmented)
+ * pointers, but this distinction is no longer needed.
+ */
+typedef ref *s_ptr;
+typedef const ref *const_s_ptr;
+
+/* Define an opaque allocator type. */
+#ifndef gs_ref_memory_DEFINED
+#  define gs_ref_memory_DEFINED
+typedef struct gs_ref_memory_s gs_ref_memory_t;
+#endif
+
+/*
+ * Define the state of a stack, other than the data it holds.
+ * Note that the total size of a stack cannot exceed max_uint,
+ * because it has to be possible to copy a stack to a PostScript array.
+ */
+#ifndef ref_stack_DEFINED
+typedef struct ref_stack_s ref_stack_t;	/* also defined in idebug.h */
+#  define ref_stack_DEFINED
+#endif
+/*
+ * We divide the stack structure into two parts: ref_stack_params_t, which
+ * is set when the stack is created and (almost) never changed after that,
+ * and ref_stack_t, which changes dynamically.
+ */
+typedef struct ref_stack_params_s ref_stack_params_t;
+struct ref_stack_s {
+    /* Following are updated dynamically. */
+    s_ptr p;			/* current top element */
+    /* Following are updated when adding or deleting blocks. */
+    s_ptr bot;			/* bottommost valid element */
+    s_ptr top;			/* topmost valid element = */
+				/* bot + data_size */
+    ref current;		/* t_array for current top block */
+    uint extension_size;	/* total sizes of extn. blocks */
+    uint extension_used;	/* total used sizes of extn. blocks */
+    /* Following are updated rarely. */
+    ref max_stack;		/* t_integer, Max...Stack user param */
+    uint requested;		/* amount of last failing */
+				/* push or pop request */
+    uint margin;		/* # of slots to leave between limit */
+				/* and top */
+    uint body_size;		/* data_size - margin */
+    /* Following are set only at initialization. */
+    ref_stack_params_t *params;
+    gs_ref_memory_t *memory;	/* allocator for params and blocks */
+};
+#define public_st_ref_stack()	/* in istack.c */\
+  gs_public_st_complex_only(st_ref_stack, ref_stack_t, "ref_stack_t",\
+    ref_stack_clear_marks, ref_stack_enum_ptrs, ref_stack_reloc_ptrs, 0)
+#define st_ref_stack_num_ptrs 2	/* current, params */
+
+#endif /* isdata_INCLUDED */