picoc/heap.c

/* stack grows up from the bottom and heap grows down from the top of heap space */
#include "picoc.h"

#define FREELIST_BUCKETS 8                          /* freelists for 4, 8, 12 ... 32 byte allocs */
#define SPLIT_MEM_THRESHOLD 16                      /* don't split memory which is close in size */

#ifdef SURVEYOR_HOST
#define HEAP_SIZE C_HEAPSIZE
static unsigned char *HeapMemory = (unsigned char *)C_HEAPSTART;      /* all memory - stack and heap */
static void *HeapBottom = (void *)C_HEAPSTART + HEAP_SIZE;  /* the bottom of the (downward-growing) heap */
static void *StackFrame = (void *)C_HEAPSTART;              /* the current stack frame */
static void *HeapStackTop = (void *)C_HEAPSTART;            /* the top of the stack */
#else
static unsigned char HeapMemory[HEAP_SIZE];         /* all memory - stack and heap */
static void *HeapBottom = &HeapMemory[HEAP_SIZE];   /* the bottom of the (downward-growing) heap */
static void *StackFrame = &HeapMemory[0];           /* the current stack frame */
void *HeapStackTop = &HeapMemory[0];                /* the top of the stack */
#endif

static struct AllocNode *FreeListBucket[FREELIST_BUCKETS];      /* we keep a pool of freelist buckets to reduce fragmentation */
static struct AllocNode *FreeListBig;                           /* free memory which doesn't fit in a bucket */

#ifdef DEBUG_HEAP
void ShowBigList()
{
    struct AllocNode *LPos;
    
    printf("Heap: bottom=0x%lx 0x%lx-0x%lx, big freelist=", (long)HeapBottom, (long)&HeapMemory[0], (long)&HeapMemory[HEAP_SIZE]);
    for (LPos = FreeListBig; LPos != NULL; LPos = LPos->NextFree)
        printf("0x%lx:%d ", (long)LPos, LPos->Size);
    
    printf("\n");
}
#endif

/* initialise the stack and heap storage */
void HeapInit()
{
    int Count;
    
    StackFrame = &HeapMemory[0];
    HeapStackTop = &HeapMemory[0];
    *(void **)StackFrame = NULL;
    HeapBottom = &HeapMemory[HEAP_SIZE];
    FreeListBig = NULL;
    for (Count = 0; Count < FREELIST_BUCKETS; Count++)
        FreeListBucket[Count] = NULL;
}

/* allocate some space on the stack, in the current stack frame
 * clears memory. can return NULL if out of stack space */
void *HeapAllocStack(int Size)
{
    void *NewMem = HeapStackTop;
    void *NewTop = HeapStackTop + MEM_ALIGN(Size);
    if (NewTop > HeapBottom)
        return NULL;
        
    HeapStackTop = NewTop;
    memset(NewMem, '\0', Size);
    return NewMem;
}

/* free some space at the top of the stack */
int HeapPopStack(void *Addr, int Size)
{
    int ToLose = MEM_ALIGN(Size);
    if (ToLose > (HeapStackTop - (void *)&HeapMemory[0]))
        return FALSE;
    
    HeapStackTop -= ToLose;
    if (HeapStackTop != Addr) 
        printf("fail\n");
    assert(HeapStackTop == Addr);
    
    return TRUE;
}

/* push a new stack frame on to the stack */
void HeapPushStackFrame()
{
#ifdef DEBUG_HEAP
    printf("Adding stack frame at 0x%lx\n", (unsigned long)HeapStackTop);
#endif
    *(void **)HeapStackTop = StackFrame;
    StackFrame = HeapStackTop;
    HeapStackTop += sizeof(void *);
}

/* pop the current stack frame, freeing all memory in the frame. can return NULL */
int HeapPopStackFrame()
{
    if (*(void **)StackFrame != NULL)
    {
        HeapStackTop = StackFrame;
        StackFrame = *(void **)StackFrame;
#ifdef DEBUG_HEAP
        printf("Popping stack frame back to 0x%lx\n", (unsigned long)HeapStackTop);
#endif
        return TRUE;
    }
    else
        return FALSE;
}

/* allocate some dynamically allocated memory. memory is cleared. can return NULL if out of memory */
void *HeapAlloc(int Size)
{
#ifdef USE_MALLOC_HEAP
    return calloc(Size, 1);
#else
    struct AllocNode *NewMem = NULL;
    struct AllocNode **FreeNode;
    int AllocSize = MEM_ALIGN(Size) + sizeof(NewMem->Size);
    int Bucket;
    
    if (Size == 0)
        return NULL;
    
    assert(Size > 0);
    
    /* make sure we have enough space for an AllocNode */
    if (AllocSize < sizeof(struct AllocNode))
        AllocSize = sizeof(struct AllocNode);
    
    Bucket = AllocSize >> 2;
    if (Bucket < FREELIST_BUCKETS && FreeListBucket[Bucket] != NULL)
    { /* try to allocate from a freelist bucket first */
#ifdef DEBUG_HEAP
        printf("allocating %d(%d) from bucket", Size, AllocSize);
#endif
        NewMem = FreeListBucket[Bucket];
        assert((unsigned long)NewMem >= (unsigned long)&HeapMemory[0] && (unsigned char *)NewMem - &HeapMemory[0] < HEAP_SIZE);
        FreeListBucket[Bucket] = *(struct AllocNode **)NewMem;
        assert(FreeListBucket[Bucket] == NULL || ((unsigned long)FreeListBucket[Bucket] >= (unsigned long)&HeapMemory[0] && (unsigned char *)FreeListBucket[Bucket] - &HeapMemory[0] < HEAP_SIZE));
        NewMem->Size = AllocSize;
    }
    else if (FreeListBig != NULL)
    { /* grab the first item from the "big" freelist we can fit in */
        for (FreeNode = &FreeListBig; *FreeNode != NULL && (*FreeNode)->Size < AllocSize; FreeNode = &(*FreeNode)->NextFree)
        {}
        
        if (*FreeNode != NULL)
        {
            assert((unsigned long)*FreeNode >= (unsigned long)&HeapMemory[0] && (unsigned char *)*FreeNode - &HeapMemory[0] < HEAP_SIZE);
            assert((*FreeNode)->Size < HEAP_SIZE && (*FreeNode)->Size > 0);
            if ((*FreeNode)->Size < Size + SPLIT_MEM_THRESHOLD)
            { /* close in size - reduce fragmentation by not splitting */
#ifdef DEBUG_HEAP
               printf("allocating %d(%d) from freelist, no split (%d)", Size, AllocSize, (*FreeNode)->Size);
#endif
                NewMem = *FreeNode;
                assert((unsigned long)NewMem >= (unsigned long)&HeapMemory[0] && (unsigned char *)NewMem - &HeapMemory[0] < HEAP_SIZE);
                *FreeNode = NewMem->NextFree;
            }
            else
            { /* split this big memory chunk */
#ifdef DEBUG_HEAP
                printf("allocating %d(%d) from freelist, split chunk (%d)", Size, AllocSize, (*FreeNode)->Size);
#endif
                NewMem = (void *)*FreeNode + (*FreeNode)->Size - AllocSize;
                assert((unsigned long)NewMem >= (unsigned long)&HeapMemory[0] && (unsigned char *)NewMem - &HeapMemory[0] < HEAP_SIZE);
                (*FreeNode)->Size -= AllocSize;
                NewMem->Size = AllocSize;
            }
        }
    }
    
    if (NewMem == NULL)
    { /* couldn't allocate from a freelist - try to increase the size of the heap area */
#ifdef DEBUG_HEAP
        printf("allocating %d(%d) at bottom of heap (0x%lx-0x%lx)", Size, AllocSize, (long)(HeapBottom - AllocSize), (long)HeapBottom);
#endif
        if (HeapBottom - AllocSize < HeapStackTop)
            return NULL;
        
        HeapBottom -= AllocSize;
        NewMem = HeapBottom;
        NewMem->Size = AllocSize;
    }
    
    memset((void *)&NewMem->NextFree, '\0', AllocSize-sizeof(NewMem->Size));
#ifdef DEBUG_HEAP
    printf(" = %lx\n", (unsigned long)&NewMem->NextFree);
#endif
    return (void *)&NewMem->NextFree;
#endif
}

/* free some dynamically allocated memory */
void HeapFree(void *Mem)
{
#ifdef USE_MALLOC_HEAP
    return free(Mem);
#else
    struct AllocNode *MemNode = (struct AllocNode *)(Mem-sizeof(int));
    int Bucket = MemNode->Size >> 2;
    
    assert((unsigned long)Mem >= (unsigned long)&HeapMemory[0] && (unsigned char *)Mem - &HeapMemory[0] < HEAP_SIZE);
    assert(MemNode->Size < HEAP_SIZE && MemNode->Size > 0);
    if (Mem == NULL)
        return;
    
    if ((void *)MemNode == HeapBottom)
    { /* pop it off the bottom of the heap, reducing the heap size */
#ifdef DEBUG_HEAP
        printf("freeing %d from bottom of heap\n", MemNode->Size);
#endif
        HeapBottom += MemNode->Size;
#ifdef DEBUG_HEAP
        ShowBigList();
#endif
    }
    else if (Bucket < FREELIST_BUCKETS)
    { /* we can fit it in a bucket */
#ifdef DEBUG_HEAP
        printf("freeing %d to bucket\n", MemNode->Size);
#endif
        assert(FreeListBucket[Bucket] == NULL || ((unsigned long)FreeListBucket[Bucket] >= (unsigned long)&HeapMemory[0] && (unsigned char *)FreeListBucket[Bucket] - &HeapMemory[0] < HEAP_SIZE));
        *(struct AllocNode **)MemNode = FreeListBucket[Bucket];
        FreeListBucket[Bucket] = (struct AllocNode *)MemNode;
    }
    else
    { /* put it in the big memory freelist */
#ifdef DEBUG_HEAP
        printf("freeing %lx:%d to freelist\n", (unsigned long)Mem, MemNode->Size);
#endif
        assert(FreeListBig == NULL || ((unsigned long)FreeListBig >= (unsigned long)&HeapMemory[0] && (unsigned char *)FreeListBig - &HeapMemory[0] < HEAP_SIZE));
        MemNode->NextFree = FreeListBig;
        FreeListBig = MemNode;
#ifdef DEBUG_HEAP
        ShowBigList();
#endif
    }
#endif
}