To allocate memory suitable for the dynamic creation of objects of different sizes, placing some larger objects automatically into doubly linked lists and assigning each a unique allocation ID number.

§1. Memory manager. This allocates memory as needed to store the numerous "objects" of different sizes, all C structures. There's no garbage collection because nothing is ever destroyed. Each "class" has its own doubly-linked list, and in each class the objects created are given unique IDs (within that type) counting upwards from 0. These IDs will be unique across all threads.

§2. Before going much further, we will need to anticipate what the memory manager wants. An "object" is a copy in memory of a C struct; thus, a plain int is not an object. The memory manager can only deal with a given type of struct if it contains three special elements, and we define those using a macro. Thus, if the user wants to allocate larger structures of type thingummy, then it needs to be defined like so:

    typedef struct thingummy {
        int whatsit;
        struct text_stream *doobrey;
    } thingummy;

The caveat about "larger structures" is that smaller objects can instead be stored in arrays, to reduce memory and speed overheads. Their structure declarations do not include the following macro; they do not have unique IDs; and they cannot be iterated over.

    int allocation_id;  Numbered from 0 upwards in creation order
    void *next_structure;  Next object in double-linked list
    void *prev_structure;  Previous object in double-linked list

§3. It is also necessary to define a constant in the following enumeration family: for thingummy, it would be thingummy_CLASS. Had it been a smaller object, it would have been thingummy_array_CLASS instead.

There is no significance to the order in which classes are registered with the memory system; the following sentinel value is not the class ID of any actual class, and simply forces the others to have IDs which are positive, since they count upwards from this.

enum unused_class_value_CLASS from 0

§4. For each type of object to be allocated, a single structure of the following design is maintained. Types which are allocated individually, like world objects, have no_allocated_together set to 1, and the doubly linked list is of the objects themselves. For types allocated in small arrays (typically of 100 objects at a time), no_allocated_together is set to the number of objects in each completed array (so, typically 100) and the doubly linked list is of the arrays.

typedef struct allocation_status_structure {
     actually needed for allocation purposes:
    int objects_allocated;  total number of objects (or arrays) ever allocated
    void *first_in_memory;  head of doubly linked list
    void *last_in_memory;  tail of doubly linked list

     used only to provide statistics for the debugging log:
    char *name_of_type;  e.g., "index_lexicon_entry_CLASS"
    int bytes_allocated;  total allocation for this type of object, not counting overhead
    int objects_count;  total number currently in existence (i.e., undeleted)
    int no_allocated_together;  number of objects in each array of this type of object
} allocation_status_structure;

§5. The memory allocator itself needs some memory, but only a fixed-size and fairly small array of the structures defined above. The allocator can safely begin as soon as this is initialised.

allocation_status_structure alloc_status[NO_DEFINED_CLASS_VALUES];

void Memory::start(void) {
    for (int i=0; i<NO_DEFINED_CLASS_VALUES; i++) {
        alloc_status[i].first_in_memory = NULL;
        alloc_status[i].last_in_memory = NULL;
        alloc_status[i].objects_allocated = 0;
        alloc_status[i].objects_count = 0;
        alloc_status[i].bytes_allocated = 0;
        alloc_status[i].no_allocated_together = 1;
        alloc_status[i].name_of_type = "unused";

§6. Architecture. The memory manager is built in three levels, with its interface to the user being entirely at level 3 (except that when it shuts down it calls a level 1 routine to free everything). Each level uses the one below it.

§7. Level 1: memory blocks. Memory is allocated in blocks within which objects are allocated as needed. The "safety margin" is the number of spare bytes left blank at the end of each object: this is done because we want to be paranoid about compilers on different architectures aligning structures to different boundaries (multiples of 4, 8, 16, etc.). Each block also ends with a firebreak of zeroes, which ought never to be touched: we want to minimise the chance of a mistake causing a memory exception which crashes the compiler, because if that happens it will be difficult to recover the circumstances from the debugging log.

define SAFETY_MARGIN 128
define BLANK_END_SIZE 256

§8. At present MEMORY_GRANULARITY is 800K. This is the quantity of memory allocated by each individual malloc call.

As of the early 2020s, typical Inform projects need around 500 blocks to be allocated, for around 400 MB of memory in all; the largest known take us into the low 10000s of blocks, for more like 8 to 10 GB. But the latter are very rare.

define MEMORY_GRANULARITY 100*1024*8  which must be divisible by 1024
int no_blocks_allocated = 0;
int total_objects_allocated = 0;  a potentially larger number, used only for the debugging log

§9. Memory blocks are stored in a linked list, and we keep track of the size of the current block: that is, the block at the tail of the list. Each memory block consists of a header structure, followed by SAFETY_MARGIN null bytes, followed by actual data.

typedef struct memblock_header {
    int block_number;
    struct memblock_header *next;
    char *the_memory;
} memblock_header;


memblock_header *first_memblock_header = NULL;  head of list of memory blocks
memblock_header *current_memblock_header = NULL;  tail of list of memory blocks

int used_in_current_memblock = 0;  number of bytes so far used in the tail memory block


§11. The actual allocation and deallocation is performed by the following pair of routines.

void Memory::allocate_another_block(void) {
    unsigned char *cp;
    memblock_header *mh;

    Allocate and zero out a block of memory, making cp point to it11.1;

    mh = (memblock_header *) cp;
    used_in_current_memblock = sizeof(memblock_header) + SAFETY_MARGIN;
    mh->the_memory = (void *) (cp + used_in_current_memblock);

    Add new block to the tail of the list of memory blocks11.2;

§11.1. Note that cp and mh are set to the same value: they merely have different pointer types as far as the C compiler is concerned.

Allocate and zero out a block of memory, making cp point to it11.1 =

    cp = (unsigned char *) (Memory::paranoid_calloc(MEMORY_GRANULARITY, 1));
    if (cp == NULL) Errors::fatal("Run out of memory: malloc failed");
    for (int i=0; i<MEMORY_GRANULARITY; i++) cp[i] = 0;

§11.2. As can be seen, memory block numbers count upwards from 0 in order of their allocation.

Add new block to the tail of the list of memory blocks11.2 =

    if (current_memblock_header == NULL) {
        mh->block_number = 0;
        first_memblock_header = mh;
    } else {
        mh->block_number = current_memblock_header->block_number + 1;
        current_memblock_header->next = mh;
    current_memblock_header = mh;

§12. Freeing all this memory again is just a matter of freeing each block in turn, but of course being careful to avoid following links in a just-freed block.

void Memory::free(void) {
    memblock_header *mh = first_memblock_header;
    while (mh != NULL) {
        memblock_header *next_mh = mh->next;
        void *p = (void *) mh;
        mh = next_mh;

§13. Level 2: memory frames and integrity checking. Within these extensive blocks of contiguous memory, we place the actual objects in between "memory frames", which are only used at present to police the integrity of memory: again, finding obscure and irritating memory-corruption bugs is more important to us than saving bytes. Each memory frame wraps either a single large object, or a single array of small objects.

define INTEGRITY_NUMBER 0x12345678  a value unlikely to be in memory just by chance
typedef struct memory_frame {
    int integrity_check;  this should always contain the INTEGRITY_NUMBER
    struct memory_frame *next_frame;  next frame in the list of memory frames
    int mem_type;  type of object stored in this frame
    int allocation_id;  allocation ID number of object stored in this frame
} memory_frame;

§14. There is a single linked list of all the memory frames, perhaps of about 10000 entries in length, beginning here. (These frames live in different memory blocks, but we don't need to worry about that.)

memory_frame *first_memory_frame = NULL;  earliest memory frame ever allocated
memory_frame *last_memory_frame = NULL;   most recent memory frame allocated

§15. If the integrity numbers of every frame are still intact, then it is pretty unlikely that any bug has caused memory to overwrite one frame into another. Memory::check_memory_integrity might on very large runs be run often, if we didn't prevent this: since the number of calls would be roughly proportional to memory usage, we would implicitly have an \(O(n^2)\) running time in the amount of storage \(n\) allocated.

int calls_to_cmi = 0;
void Memory::check_memory_integrity(void) {
    int c;
    memory_frame *mf;
    c = calls_to_cmi++;
    if (!((c<10) || (c == 100) || (c == 1000) || (c == 10000))) return;

    for (c = 0, mf = first_memory_frame; mf; c++, mf = mf->next_frame)
        if (mf->integrity_check != INTEGRITY_NUMBER)
            Errors::fatal("Memory manager failed integrity check");

void Memory::debug_memory_frames(int from, int to) {
    int c;
    memory_frame *mf;
    for (c = 0, mf = first_memory_frame; (mf) && (c <= to); c++, mf = mf->next_frame)
        if (c >= from) {
            char *desc = "corrupt";
            if (mf->integrity_check == INTEGRITY_NUMBER)
                desc = alloc_status[mf->mem_type].name_of_type;

§16. We have seen how memory is allocated in large blocks, and that a linked list of memory frames will live inside those blocks; we have seen how the list is checked for integrity; but we not seen how it is built. Every memory frame is created by the following function:

void *Memory::allocate(int mem_type, int extent) {
    unsigned char *cp;
    memory_frame *mf;
    int bytes_free_in_current_memblock, extent_without_overheads = extent;

    extent += sizeof(memory_frame);  each allocation is preceded by a memory frame
    extent += SAFETY_MARGIN;  each allocation is followed by SAFETY_MARGIN null bytes

    Ensure that the current memory block has room for this many bytes16.1;

    cp = ((unsigned char *) (current_memblock_header->the_memory)) + used_in_current_memblock;
    used_in_current_memblock += extent;

    mf = (memory_frame *) cp;  the new memory frame,
    cp = cp + sizeof(memory_frame);  following which is the actual allocated data

    mf->integrity_check = INTEGRITY_NUMBER;
    mf->allocation_id = alloc_status[mem_type].objects_allocated;
    mf->mem_type = mem_type;

    Add the new memory frame to the big linked list of all frames16.2;
    Update the allocation status for this type of object16.3;

    return (void *) cp;

§16.1. The granularity error below will be triggered the first time a particular object type is allocated. So this is not a potential time-bomb just waiting for a user with a particularly long and involved source text to discover.

Ensure that the current memory block has room for this many bytes16.1 =

    if (current_memblock_header == NULL) Memory::allocate_another_block();
    bytes_free_in_current_memblock = MEMORY_GRANULARITY - (used_in_current_memblock + extent);
    if (bytes_free_in_current_memblock < BLANK_END_SIZE) {
            Errors::fatal("Memory manager failed because granularity too low");

§16.2. New memory frames are added to the tail of the list:

Add the new memory frame to the big linked list of all frames16.2 =

    mf->next_frame = NULL;
    if (first_memory_frame == NULL) first_memory_frame = mf;
    else last_memory_frame->next_frame = mf;
    last_memory_frame = mf;

§16.3. See the definition of alloc_status above.

Update the allocation status for this type of object16.3 =

    if (alloc_status[mem_type].first_in_memory == NULL)
        alloc_status[mem_type].first_in_memory = (void *) cp;
    alloc_status[mem_type].last_in_memory = (void *) cp;
    alloc_status[mem_type].bytes_allocated += extent_without_overheads;

§17. Level 3: managing linked lists of allocated objects. We define macros which look as if they are functions, but for which one argument is the name of a type: expanding these macros provides suitable C functions to handle each possible type. These macros provide the interface through which all other sections allocate and leaf through memory.

Note that Inweb allows multi-line macro definitions without backslashes to continue them, unlike ordinary C. Otherwise these are "standard" macros, though this was my first brush with the ## concatenation operator: basically CREATE(thing) expands into (allocate_thing()) because of the ##. (See Kernighan and Ritchie, section 4.11.2.)

define CREATE(type_name) (allocate_##type_name())
define COPY(to, from, type_name) (copy_##type_name(to, from))
define CREATE_BEFORE(existing, type_name) (allocate_##type_name##_before(existing))
define DESTROY(this, type_name) (deallocate_##type_name(this))
define FIRST_OBJECT(type_name) ((type_name *) alloc_status[type_name##_CLASS].first_in_memory)
define LAST_OBJECT(type_name) ((type_name *) alloc_status[type_name##_CLASS].last_in_memory)
define NEXT_OBJECT(this, type_name) ((type_name *) (this->next_structure))
define PREV_OBJECT(this, type_name) ((type_name *) (this->prev_structure))
define NUMBER_CREATED(type_name) (alloc_status[type_name##_CLASS].objects_count)

§18. The following macros are widely used (well, the first one is, anyway) for looking through the double linked list of existing objects of a given type.

define LOOP_OVER(var, type_name)
    for (var=FIRST_OBJECT(type_name); var != NULL; var = NEXT_OBJECT(var, type_name))
define LOOP_BACKWARDS_OVER(var, type_name)
    for (var=LAST_OBJECT(type_name); var != NULL; var = PREV_OBJECT(var, type_name))

§19. Allocator functions created by macros. The following macros generate a family of systematically named functions. For instance, we shall shortly expand DECLARE_CLASS(parse_node), which will expand to three functions: allocate_parse_node, deallocate_parse_node and allocate_parse_node_before.

Quaintly, #type_name expands into the value of type_name put within double-quotes.

define NEW_OBJECT(type_name) ((type_name *) Memory::allocate(type_name##_CLASS, sizeof(type_name)))
define DECLARE_CLASS(type_name) DECLARE_CLASS_WITH_ID(type_name, type_name##_CLASS)
define DECLARE_CLASS_WITH_ID(type_name, id_name)
MAKE_REFERENCE_ROUTINES(type_name, id_name)
type_name *allocate_##type_name(void) {
    alloc_status[id_name].name_of_type = #type_name;
    type_name *prev_obj = LAST_OBJECT(type_name);
    type_name *new_obj = Memory::allocate(type_name##_CLASS, sizeof(type_name));
    new_obj->allocation_id = alloc_status[id_name].objects_allocated-1;
    new_obj->next_structure = NULL;
    if (prev_obj != NULL)
        prev_obj->next_structure = (void *) new_obj;
    new_obj->prev_structure = prev_obj;
    return new_obj;
void deallocate_##type_name(type_name *kill_me) {
    type_name *prev_obj = PREV_OBJECT(kill_me, type_name);
    type_name *next_obj = NEXT_OBJECT(kill_me, type_name);
    if (prev_obj == NULL) {
        alloc_status[id_name].first_in_memory = next_obj;
    } else {
        prev_obj->next_structure = next_obj;
    if (next_obj == NULL) {
        alloc_status[id_name].last_in_memory = prev_obj;
    } else {
        next_obj->prev_structure = prev_obj;
type_name *allocate_##type_name##_before(type_name *existing) {
    type_name *new_obj = allocate_##type_name();
    new_obj->prev_structure = existing->prev_structure;
    if (existing->prev_structure != NULL)
        ((type_name *) existing->prev_structure)->next_structure = new_obj;
    else alloc_status[id_name].first_in_memory = (void *) new_obj;
    new_obj->next_structure = existing;
    existing->prev_structure = new_obj;
    return new_obj;
void copy_##type_name(type_name *to, type_name *from) {
    type_name *prev_obj = to->prev_structure;
    type_name *next_obj = to->next_structure;
    int aid = to->allocation_id;
    *to = *from;
    to->allocation_id = aid;
    to->next_structure = next_obj;
    to->prev_structure = prev_obj;

§20. DECLARE_CLASS_ALLOCATED_IN_ARRAYS is still more obfuscated. When we DECLARE_CLASS_ALLOCATED_IN_ARRAYS(X, 100), the result will be definitions of a new type X_array and constructors for both X and X_array, the former of which uses the latter. Note that we are not provided with the means to deallocate individual objects this time: that's the trade-off for allocating in blocks.

MAKE_REFERENCE_ROUTINES(type_name, type_name##_CLASS)
typedef struct type_name##_array {
    int used;
    struct type_name array[NO_TO_ALLOCATE_TOGETHER];
} type_name##_array;
int type_name##_array_CLASS = type_name##_CLASS;  C does permit #define to make #defines
DECLARE_CLASS_WITH_ID(type_name##_array, type_name##_CLASS)
type_name##_array *next_##type_name##_array = NULL;
struct type_name *allocate_##type_name(void) {
    if ((next_##type_name##_array == NULL) ||
        (next_##type_name##_array->used >= NO_TO_ALLOCATE_TOGETHER)) {
        alloc_status[type_name##_array_CLASS].no_allocated_together = NO_TO_ALLOCATE_TOGETHER;
        next_##type_name##_array = allocate_##type_name##_array();
        next_##type_name##_array->used = 0;
    type_name *rv = &(next_##type_name##_array->array[next_##type_name##_array->used++]);
    return rv;

§21. Simple memory allocations. Not all of our memory will be claimed in the form of structures: now and then we need to use the equivalent of traditional malloc and calloc routines.

enum STREAM_MREASON from 0
void Memory::name_fundamental_reasons(void) {
    Memory::reason_name(STREAM_MREASON, "text stream storage");
    Memory::reason_name(FILENAME_STORAGE_MREASON, "filename/pathname storage");
    Memory::reason_name(STRING_STORAGE_MREASON, "string storage");
    Memory::reason_name(DICTIONARY_MREASON, "dictionary storage");
    Memory::reason_name(ARRAY_SORTING_MREASON, "sorting");

§22. And here is the (very simple) implementation.

char *memory_needs[NO_DEFINED_MREASON_VALUES];

void Memory::reason_name(int r, char *reason) {
    if ((r < 0) || (r >= NO_DEFINED_MREASON_VALUES)) internal_error("MR out of range");
    memory_needs[r] = reason;

char *Memory::description_of_reason(int r) {
    if ((r < 0) || (r >= NO_DEFINED_MREASON_VALUES)) internal_error("MR out of range");
    return memory_needs[r];

§23. We keep some statistics on this. The value for "memory claimed" is the net amount of memory currently owned, which is increased when we allocate it and decreased when we free it. Whether the host OS is able to make efficient use of the memory we free, we can't know, but it probably is, and therefore the best estimate of how well we're doing is the "maximum memory claimed" — the highest recorded net usage count over the run.

int max_memory_at_once_for_each_need[NO_DEFINED_MREASON_VALUES],
int total_claimed_simply = 0;

§24. Our allocation routines behave just like the standard C library's malloc and calloc, but where a third argument supplies a reason why the memory is needed, and where any failure to allocate memory is tidily dealt with. We will exit on any such failure, so that the caller can be certain that the return values of these functions are always non-NULL pointers.

void *Memory::calloc(int how_many, int size_in_bytes, int reason) {
    return Memory::alloc_inner(how_many, size_in_bytes, reason);
void *Memory::malloc(int size_in_bytes, int reason) {
    return Memory::alloc_inner(-1, size_in_bytes, reason);

§25. And this, then, is the joint routine implementing both.

void *Memory::alloc_inner(int N, int S, int R) {
    void *pointer;
    int bytes_needed;
    if ((R < 0) || (R >= NO_DEFINED_MREASON_VALUES)) internal_error("no such memory reason");
    if (total_claimed_simply == 0) Zero out the statistics on simple memory allocations25.2;
    Claim the memory using malloc or calloc as appropriate25.1;
    Update the statistics on simple memory allocations25.3;
    return pointer;

§25.1. I am nervous about assuming that calloc(0, X) returns a non-NULL pointer in all implementations of the standard C library, so the case when N is zero allocates a tiny but positive amount of memory, just to be safe.

Claim the memory using malloc or calloc as appropriate25.1 =

    if (N > 0) {
        pointer = Memory::paranoid_calloc((size_t) N, (size_t) S);
        bytes_needed = N*S;
    } else {
        pointer = Memory::paranoid_calloc(1, (size_t) S);
        bytes_needed = S;
    if (pointer == NULL) {
        Errors::fatal_with_C_string("Out of memory for %s", Memory::description_of_reason(R));

§25.2. These statistics have no function except to improve the diagnostics in the debugging log, but they are very cheap to keep, since Memory::alloc_inner is called only rarely and to allocate large blocks of memory.

Zero out the statistics on simple memory allocations25.2 =

    for (int i=0; i<NO_DEFINED_MREASON_VALUES; i++) {
        max_memory_at_once_for_each_need[i] = 0;
        memory_claimed_for_each_need[i] = 0;
        number_of_claims_for_each_need[i] = 0;

§25.3. Update the statistics on simple memory allocations25.3 =

    memory_claimed_for_each_need[R] += bytes_needed;
    total_claimed_simply += bytes_needed;
    if (memory_claimed_for_each_need[R] > max_memory_at_once_for_each_need[R])
        max_memory_at_once_for_each_need[R] = memory_claimed_for_each_need[R];

§26. We also provide our own wrapper for free:

void Memory::I7_free(void *pointer, int R, int bytes_freed) {
    if ((R < 0) || (R >= NO_DEFINED_MREASON_VALUES)) internal_error("no such memory reason");
    if (pointer == NULL) internal_error("can't free NULL memory");
    memory_claimed_for_each_need[R] -= bytes_freed;

void Memory::I7_array_free(void *pointer, int R, int num_cells, size_t cell_size) {
    Memory::I7_free(pointer, R, num_cells*((int) cell_size));

§27. Memory usage report. A small utility routine to help keep track of our unquestioned profligacy.

void Memory::log_statistics(void) {
    int total_for_objects = MEMORY_GRANULARITY*no_blocks_allocated;  usage in bytes
    int total_for_SMAs = Memory::log_usage(0);  usage in bytes
    int sorted_usage[NO_DEFINED_CLASS_VALUES];  memory type numbers, in usage order
    int total = (total_for_objects + total_for_SMAs)/1024;  total memory usage in KB

    Sort the table of memory type usages into decreasing size order27.2;

    int total_for_objects_used = 0;  out of the total_for_objects, the bytes used
    int total_objects = 0;
    Calculate the memory usage for objects27.1;
    int overhead_for_objects = total_for_objects - total_for_objects_used;  bytes wasted
    Print the report to the debugging log27.3;

§27.1. Calculate the memory usage for objects27.1 =

    int i, j;
    for (j=0; j<NO_DEFINED_CLASS_VALUES; j++) {
        i = sorted_usage[j];
        if (alloc_status[i].objects_allocated != 0) {
            if (alloc_status[i].no_allocated_together == 1)
                total_objects += alloc_status[i].objects_allocated;
                total_objects += alloc_status[i].objects_allocated*
            total_for_objects_used += alloc_status[i].bytes_allocated;

§27.2. This is the criterion for sorting memory types in the report: descending order of total number of bytes allocated.

Sort the table of memory type usages into decreasing size order27.2 =

    for (int i=0; i<NO_DEFINED_CLASS_VALUES; i++) sorted_usage[i] = i;
    qsort(sorted_usage, (size_t) NO_DEFINED_CLASS_VALUES, sizeof(int), Memory::compare_usage);

§27.3. And here is the actual report:

Print the report to the debugging log27.3 =

    LOG("Total memory consumption was %dK = %d MB\n\n",
        total, (total+512)/1024);

    Memory::log_percentage(total_for_objects, total);
    LOG(" was used for %d objects, in %d frames in %d x %dK = %dK = %d MB:\n\n",
        total_objects, total_objects_allocated, no_blocks_allocated,
        total_for_objects/1024, (total_for_objects+512)/1024/1024);
    for (int j=0; j<NO_DEFINED_CLASS_VALUES; j++) {
        int i = sorted_usage[j];
        if (alloc_status[i].objects_allocated != 0) {
            LOG("    ");
            Memory::log_percentage(alloc_status[i].bytes_allocated, total);
            LOG("  %s", alloc_status[i].name_of_type);
            for (int n=(int) strlen(alloc_status[i].name_of_type); n<41; n++) LOG(" ");
            if (alloc_status[i].no_allocated_together == 1) {
                LOG("%d ", alloc_status[i].objects_count);
                if (alloc_status[i].objects_count != alloc_status[i].objects_allocated)
                    LOG("(+%d deleted) ",
                        alloc_status[i].objects_allocated - alloc_status[i].objects_count);
                if (alloc_status[i].objects_allocated > 1) LOG("s");
            } else {
                if (alloc_status[i].objects_allocated > 1)
                    LOG("%d x %d = %d ",
                    alloc_status[i].objects_allocated, alloc_status[i].no_allocated_together,
                    LOG("1 x %d ", alloc_status[i].no_allocated_together);
            LOG(", %d bytes\n", alloc_status[i].bytes_allocated);
    Memory::log_percentage(1024*total-total_for_objects, total);
    LOG(" was used for memory not allocated for objects:\n\n");
    LOG("\n"); Memory::log_percentage(overhead_for_objects, total);
    LOG(" was overhead - %d bytes = %dK = %d MB\n\n", overhead_for_objects,
        overhead_for_objects/1024, (overhead_for_objects+512)/1024/1024);


int Memory::log_usage(int total) {
    if (total_claimed_simply == 0) return 0;
    int i, t = 0;
    for (i=0; i<NO_DEFINED_MREASON_VALUES; i++) {
        t += max_memory_at_once_for_each_need[i];
        if ((total > 0) && (max_memory_at_once_for_each_need[i] > 0)) {
            LOG("    ");
            Memory::log_percentage(max_memory_at_once_for_each_need[i], total);
            LOG("  %s", Memory::description_of_reason(i));
            for (int n=(int) strlen(Memory::description_of_reason(i)); n<41; n++) LOG(" ");
            LOG("%d bytes in %d claim%s\n",
                (number_of_claims_for_each_need[i] == 1)?"":"s");
    return t;


int Memory::compare_usage(const void *ent1, const void *ent2) {
    int ix1 = *((const int *) ent1);
    int ix2 = *((const int *) ent2);
    return alloc_status[ix2].bytes_allocated - alloc_status[ix1].bytes_allocated;

§30. Finally, a little routine to compute the proportions of memory for each usage. Recall that bytes is measured in bytes, but total in kilobytes.

void Memory::log_percentage(int bytes, int total) {
    float B = (float) bytes, T = (float) total;
    float P = (1000*B)/(1024*T);
    int N = (int) P;
    if (N == 0) LOG(" ----");
    else LOG("%2d.%01d%%", N/10, N%10);

§31. At one time, the following function was paranoid about thread-safety of calloc as implemented in some C libraries, and was protected by a mutex. It has now learned to chill.

void *Memory::paranoid_calloc(size_t N, size_t S) {
    void *P = calloc(N, S);
    return P;

§32. Run-time pointer type checking. In several places Inform needs to store pointers of type void *, that is, pointers which have no indication of what type of data they point to. This is not type-safe and therefore offers plenty of opportunity for blunders. The following provides run-time type checking to ensure that each time we dereference a typeless pointer, it does indeed point to a structure of the type we think it should.

The structure general_pointer holds a void * pointer to any one of the following:

define NULL_GENERAL_POINTER (Memory::store_gp_null())
define GENERAL_POINTER_IS_NULL(gp) (Memory::test_gp_null(gp))
typedef struct general_pointer {
    void *pointer_to_data;
    int run_time_type_code;
} general_pointer;

general_pointer Memory::store_gp_null(void) {
    general_pointer gp;
    gp.pointer_to_data = NULL;
    gp.run_time_type_code = -1;  guaranteed to differ from all _CLASS values
    return gp;
int Memory::test_gp_null(general_pointer gp) {
    if (gp.run_time_type_code == -1) return TRUE;
    return FALSE;

§33. The symbols tables need to look at pointer values directly without knowing their types, but only to test equality, so we abstract that thus. And the debugging log also shows actual hexadecimal addresses to distinguish nameless objects and to help with interpreting output from GDB, so we abstract that too.

    (gp1.pointer_to_data == gp2.pointer_to_data)
    ((pointer_sized_int) gp.pointer_to_data)

§34. If we have a pointer to circus (say) then g=STORE_POINTER_circus(p) returns a general_pointer with p as the actual pointer, but will not compile unless p is indeed of type circus *. When we later RETRIEVE_POINTER_circus(g), an internal error is thrown if g contains a pointer which is other than void *, or which has never been referenced.

define MAKE_REFERENCE_ROUTINES(type_name, id_code)
general_pointer STORE_POINTER_##type_name(type_name *data) {
    general_pointer gp;
    gp.pointer_to_data = (void *) data;
    gp.run_time_type_code = id_code;
    return gp;
type_name *RETRIEVE_POINTER_##type_name(general_pointer gp) {
    if (gp.run_time_type_code != id_code) {
        LOG("Wanted ID code %d, found %d\n", id_code, gp.run_time_type_code);
        internal_error("attempt to retrieve wrong pointer type as " #type_name);
    return (type_name *) gp.pointer_to_data;
general_pointer PASS_POINTER_##type_name(general_pointer gp) {
    if (gp.run_time_type_code != id_code) {
        LOG("Wanted ID code %d, found %d\n", id_code, gp.run_time_type_code);
        internal_error("attempt to pass wrong pointer type as " #type_name);
    return gp;
int VALID_POINTER_##type_name(general_pointer gp) {
    if (gp.run_time_type_code == id_code) return TRUE;
    return FALSE;

§35. Suitable MAKE_REFERENCE_ROUTINES were expanded for all of the memory allocated objects above; so that leaves only humble char * pointers: