vn/code/core/core_memory.cpp

//- sixten: Common memory functions

static void Copy(void *Dest, void *Source, umm Count)
{
    u8 *Dest8 = (u8 *)Dest;
    u8 *Source8 = (u8 *)Source;
    
    while(Count--)
    {
        *Dest8++ = *Source8++;
    }
}

static void Fill(void *Dest, u8 Value, umm Count)
{
    u8 *Dest8 = (u8 *)Dest;
    
    while(Count--)
    {
        *Dest8++ = Value;
    }
}

//- sixten: Memory arena functions

static void Release(memory_arena *Arena)
{
    while(Arena->CurrentBlock != 0)
    {
        platform_memory_block *MemoryBlock = Arena->CurrentBlock;
        b32 IsLastBlock = (MemoryBlock->ArenaPrev  == 0);
        Arena->CurrentBlock = MemoryBlock->ArenaPrev;
        Platform.DeallocateMemory(MemoryBlock);
        
        if(IsLastBlock)
        {
            break;
        }
    }
}

inline umm GetAlignmentOffset(memory_arena *Arena, umm Alignment)
{
    umm AlignmentOffset = 0;
    
    umm ResultPointer = (umm)Arena->CurrentBlock + Arena->CurrentBlock->Used;
    umm AlignmentMask = Alignment - 1;
    if(ResultPointer & AlignmentMask)
    {
        AlignmentOffset = Alignment - (ResultPointer & AlignmentMask);
    }
    
    return(AlignmentOffset);
}

inline umm GetEffectiveSizeFor(memory_arena *Arena, umm InitialSize, arena_push_params Params)
{
    umm Size = InitialSize;
    
    umm AlignmentOffset = GetAlignmentOffset(Arena, Params.Alignment);
    Size += AlignmentOffset;
    
    return(Size);
}

static void *PushSize_(memory_arena *Arena, umm InitialSize, arena_push_params Params)
{
    void *Result = 0;
    
    umm Size = 0;
    if(Arena->CurrentBlock)
    {
        Size = GetEffectiveSizeFor(Arena, InitialSize, Params);
    }
    
    if(!Arena->CurrentBlock || ((Arena->CurrentBlock->Used + Size) > Arena->CurrentBlock->Size))
    {
        Size = InitialSize;
        
        if(!Arena->MinimumBlockSize)
        {
            Arena->MinimumBlockSize = 1024*1024;
        }
        
        umm BlockSize = Maximum(Size, Arena->MinimumBlockSize);
        
        platform_memory_block *NewBlock = Platform.AllocateMemory(BlockSize);
        NewBlock->ArenaPrev = Arena->CurrentBlock;
        Arena->CurrentBlock = NewBlock;
    }
    
    Assert((Arena->CurrentBlock->Used + Size) <= Arena->CurrentBlock->Size);
    
    umm AlignmentOffset = GetAlignmentOffset(Arena, Params.Alignment);
    umm OffsetInBlock = Arena->CurrentBlock->Used + AlignmentOffset;
    Result = Arena->CurrentBlock->Base + OffsetInBlock;
    Arena->CurrentBlock->Used += Size;
    
    Assert(Size >= InitialSize);
    Assert(Arena->CurrentBlock->Used <= Arena->CurrentBlock->Size);
    
    if(Params.Flags & ArenaFlag_ClearToZero)
    {
        Fill(Result, 0, InitialSize);
    }
    
    return(Result);
}

//- sixten: Bootsrapping helpers

static void *BootstrapPushSize(umm Size, umm OffsetToArena)
{
    memory_arena Arena = {};
    void *Result = PushSize(&Arena, Size);
    *(memory_arena *)((u8 *)Result + OffsetToArena) = Arena;
    
    return(Result);
}

//- sixten: Temporary memory functions

static temporary_memory BeginTemporaryMemory(memory_arena *Arena)
{
    temporary_memory Result;
    Result.Arena = Arena;
    Result.Block = Arena->CurrentBlock;
    Result.Used = Arena->CurrentBlock ? Arena->CurrentBlock->Used : 0;
    
    ++Arena->TemporaryMemoryCount;
    
    return(Result);
}

static void EndTemporaryMemory(temporary_memory Temp)
{
    memory_arena *Arena = Temp.Arena;
    while(Arena->CurrentBlock != Temp.Block)
    {
        platform_memory_block *MemoryBlock = Arena->CurrentBlock;
        Arena->CurrentBlock = MemoryBlock->ArenaPrev;
        Platform.DeallocateMemory(MemoryBlock);
    }
    
    if(Arena->CurrentBlock)
    {
        Assert(Arena->CurrentBlock->Used >= Temp.Used);
        Arena->CurrentBlock->Used = Temp.Used;
    }
    
    Assert(Arena->TemporaryMemoryCount > 0);
    --Arena->TemporaryMemoryCount;
}