Initial commit.

This first sketch of the memory layout isn't working because I'm
not succeeding in packing the bitfields, so I intend to rip it up
and start again.

src/memory.h

@@ -0,0 +1,94 @@
+/**
+ *  memory.h
+ *
+ *  Grendel: a compiling Beowulf reimplementation.
+ *
+ *  The memory management subsystem.
+ *
+ *  (c) 2026 Simon Brooke <simon@journeyman.cc>
+ *  Licensed under GPL version 2.0, or, at your option, any later version.
+ */
+
+#ifndef __grendel_memory_h
+#define __grendel_memory_h
+
+#include <stdint.h>
+
+/* Tags for 32 bit objects, with 3 bits of tag an one mark bit */
+
+/**
+ * This pointer object is an actual pointer -- an offset into consspace.
+ */
+#define OFFSETTV 		0
+/**
+ * This pointer object is actually a 28 bit integer value.
+ */
+#define INTEGERTV 		1
+/*
+ * Values 2..6 inclusive reserved further data types, including maybe
+ * implementing reals later.
+ */
+
+/**
+ * This is not actually a pointer at all but the first word of a cell.
+ */
+#define CELLTV			7
+
+/**
+ * Half of a cons cell. The mark bit is first, so that the ptag can be
+ * considered as part of the CTAG.
+ */
+struct pointer {
+	/* mark bit for mark and sweep garbage collector. Yes, this is normally
+	 * thought of as part of the cell, but bear with me. */
+	unsigned int mark : 1;
+	/* pointer tag, interpretations as above */
+	unsigned int ptag : 3;
+	/* the actual payload of the pointer object */
+	union {
+		unsigned int offset : 28;
+		int value : 28;
+	} payload;
+};
+
+struct cons_payload {
+	struct pointer pointers[2];
+};
+
+struct symbol_payload {
+	/* this is the same mark bit as the one in the `address` pointer of the
+	 * cons_payload. */
+	unsigned int mark : 1;
+	unsigned int tag : 7;
+	char symbol[7];
+};
+
+/* Tags for 64 bit objects. Note that, as the 64 bit object may be made up
+ * of two 32 bit objects (pointers*, the 64 bit tag is stored in bits 4..7
+ * inclusive. The first three bits are the first three bits of a 32 bit object,
+ * and thus for 64bit objects will always b 111.*/
+
+/* this 64 bit object is a cons cell */
+#define CONSTV 7
+
+/* this 64 bit object is a seven character atom */
+#define ATOMTV 8
+
+/* There are potentially another 119 types of object we could store in a 64
+ * bit object, but I can't think of any we need just now. */
+
+struct cell {
+	union {
+		struct cons_payload cons;
+		struct symbol_payload symbol;
+	} payload;
+};
+
+#define CONSSPACESIZE 65536
+
+/**
+ * The entire array of cells available to the system.
+ */
+struct cell consspace[CONSSPACESIZE];
+
+#endif