Simon Brooke
7e9dc12766
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.
94 lines
2.2 KiB
C
94 lines
2.2 KiB
C
/**
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* memory.h
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*
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* Grendel: a compiling Beowulf reimplementation.
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*
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* The memory management subsystem.
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*
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* (c) 2026 Simon Brooke <simon@journeyman.cc>
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* Licensed under GPL version 2.0, or, at your option, any later version.
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*/
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#ifndef __grendel_memory_h
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#define __grendel_memory_h
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#include <stdint.h>
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/* Tags for 32 bit objects, with 3 bits of tag an one mark bit */
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/**
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* This pointer object is an actual pointer -- an offset into consspace.
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*/
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#define OFFSETTV 0
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/**
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* This pointer object is actually a 28 bit integer value.
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*/
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#define INTEGERTV 1
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/*
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* Values 2..6 inclusive reserved further data types, including maybe
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* implementing reals later.
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*/
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/**
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* This is not actually a pointer at all but the first word of a cell.
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*/
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#define CELLTV 7
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/**
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* Half of a cons cell. The mark bit is first, so that the ptag can be
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* considered as part of the CTAG.
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*/
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struct pointer {
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/* mark bit for mark and sweep garbage collector. Yes, this is normally
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* thought of as part of the cell, but bear with me. */
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unsigned int mark : 1;
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/* pointer tag, interpretations as above */
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unsigned int ptag : 3;
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/* the actual payload of the pointer object */
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union {
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unsigned int offset : 28;
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int value : 28;
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} payload;
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};
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struct cons_payload {
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struct pointer pointers[2];
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};
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struct symbol_payload {
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/* this is the same mark bit as the one in the `address` pointer of the
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* cons_payload. */
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unsigned int mark : 1;
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unsigned int tag : 7;
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char symbol[7];
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};
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/* Tags for 64 bit objects. Note that, as the 64 bit object may be made up
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* of two 32 bit objects (pointers*, the 64 bit tag is stored in bits 4..7
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* inclusive. The first three bits are the first three bits of a 32 bit object,
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* and thus for 64bit objects will always b 111.*/
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/* this 64 bit object is a cons cell */
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#define CONSTV 7
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/* this 64 bit object is a seven character atom */
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#define ATOMTV 8
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/* There are potentially another 119 types of object we could store in a 64
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* bit object, but I can't think of any we need just now. */
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struct cell {
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union {
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struct cons_payload cons;
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struct symbol_payload symbol;
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} payload;
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};
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#define CONSSPACESIZE 65536
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/**
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* The entire array of cells available to the system.
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*/
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struct cell consspace[CONSSPACESIZE];
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#endif
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