Mem

gistfile1.c

// Copyright (c) 2020 Christoffer Lerno. All rights reserved.
// Use of this source code is governed by a LGPLv3.0
// a copy of which can be found in the LICENSE file.

#include "vmem.h"
#include "common.h"

#if defined( _WIN32 ) || defined( __WIN32__ ) || defined( _WIN64 )
#define PLATFORM_WINDOWS 1
#define PLATFORM_POSIX 0
#else
#define PLATFORM_WINDOWS 0
#define PLATFORM_POSIX 1
#endif

#if PLATFORM_POSIX
#include <sys/mman.h>
#endif

#if PLATFORM_WINDOWS
#include <Windows.h>
#define COMMIT_PAGE_SIZE 0x10000
#endif

typedef struct
{
	void *ptr;
	size_t allocated;
#if PLATFORM_WINDOWS
	size_t committed;
#endif
} Vmem;

static void* mmap_os(Vmem *vmem, size_t size)
{
#if PLATFORM_WINDOWS
	void* ptr = VirtualAlloc(0, size, MEM_RESERVE, PAGE_NOACCESS);
	vmem->committed = 0;
	if (!ptr)
	{
		FATAL_ERROR("Failed to map virtual memory block");
	}
#elif PLATFORM_POSIX
	void* ptr = mmap(0, size, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANON | MAP_NORESERVE, -1, 0);
	if ((ptr == MAP_FAILED) || !ptr)
	{
		FATAL_ERROR("Failed to map virtual memory block");
	}
#else
	FATAL_ERROR("Unsupported platform.");
#endif
	vmem->ptr = vmem;
	vmem->allocated = 0;
	return ptr;
}

static void* mmap_allocate(Vmem *vmem, size_t to_allocate)
{
	size_t allocated_after = to_allocate + vmem->allocated;
#if PLATFORM_WINDOWS
	size_t blocks_committed = vmem->committed / COMMIT_PAGE_SIZE;
	size_t end_block = (allocated_after) / COMMIT_PAGE_SIZE;
	size_t blocks_to_allocate = end_block - blocks_committed;
	if (blocks_to_allocate > 0)
	{
		size_t to_commit = blocks_to_allocate * COMMIT_PAGE_SIZE;
		void *res = VirtualAlloc(vmem->ptr + vmem->committed, to_commit, MEM_COMMIT, PAGE_READWRITE);
		if (!res) FATAL_ERROR("Failed to allocate more memory.");
		vmem->committed += to_commit;
	}
#endif
	void *ptr = vmem->ptr + vmem->allocated;
	vmem->allocated = allocated_after;
	return ptr;
}