memio.c

//
// Copyright(C) 1993-1996 Id Software, Inc.
// Copyright(C) 2005-2014 Simon Howard
//
// This program is free software; you can redistribute it and/or
// modify it under the terms of the GNU General Public License
// as published by the Free Software Foundation; either version 2
// of the License, or (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// Emulates the IO functions in C stdio.h reading and writing to 
// memory.
//

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include "memio.h"

#include "z_zone.h"

typedef enum {
	MODE_READ,
	MODE_WRITE,
} memfile_mode_t;

struct _MEMFILE {
	unsigned char *buf;
	size_t buflen;
	size_t alloced;
	unsigned int position;
	memfile_mode_t mode;
};

// Open a memory area for reading

MEMFILE *mem_fopen_read(void *buf, size_t buflen)
{
	MEMFILE *file;

	file = Z_Malloc(sizeof(MEMFILE), PU_STATIC, 0);

	file->buf = (unsigned char *) buf;
	file->buflen = buflen;
	file->position = 0;
	file->mode = MODE_READ;

	return file;
}

// Read bytes

size_t mem_fread(void *buf, size_t size, size_t nmemb, MEMFILE *stream)
{
	size_t items;

	if (stream->mode != MODE_READ)
	{
		printf("not a read stream\n");
		return -1;
	}

	// Trying to read more bytes than we have left?
	
	items = nmemb;

	if (items * size > stream->buflen - stream->position) 
	{
		items = (stream->buflen - stream->position) / size;
	}
	
	// Copy bytes to buffer
	
	memcpy(buf, stream->buf + stream->position, items * size);

	// Update position

	stream->position += items * size;
	
	return items;
}

// Open a memory area for writing

MEMFILE *mem_fopen_write(void)
{
	MEMFILE *file;

	file = Z_Malloc(sizeof(MEMFILE), PU_STATIC, 0);

	file->alloced = 1024;
	file->buf = Z_Malloc(file->alloced, PU_STATIC, 0);
	file->buflen = 0;
	file->position = 0;
	file->mode = MODE_WRITE;

	return file;
}

// Write bytes to stream

size_t mem_fwrite(const void *ptr, size_t size, size_t nmemb, MEMFILE *stream)
{
	size_t bytes;

	if (stream->mode != MODE_WRITE)
	{
		return -1;
	}
	
	// More bytes than can fit in the buffer?
	// If so, reallocate bigger.

	bytes = size * nmemb;
	
	while (bytes > stream->alloced - stream->position)
	{
		unsigned char *newbuf;

		newbuf = Z_Malloc(stream->alloced * 2, PU_STATIC, 0);
		memcpy(newbuf, stream->buf, stream->alloced);
		Z_Free(stream->buf);
		stream->buf = newbuf;
		stream->alloced *= 2;
	}

	// Copy into buffer
	
	memcpy(stream->buf + stream->position, ptr, bytes);
	stream->position += bytes;

	if (stream->position > stream->buflen)
		stream->buflen = stream->position;

	return nmemb;
}

void mem_get_buf(MEMFILE *stream, void **buf, size_t *buflen)
{
	*buf = stream->buf;
	*buflen = stream->buflen;
}

void mem_fclose(MEMFILE *stream)
{
	if (stream->mode == MODE_WRITE)
	{
		Z_Free(stream->buf);
	}

	Z_Free(stream);
}

long mem_ftell(MEMFILE *stream)
{
	return stream->position;
}

int mem_fseek(MEMFILE *stream, signed long position, mem_rel_t whence)
{
	unsigned int newpos;

	switch (whence)
	{
		case MEM_SEEK_SET:
			newpos = (int) position;
			break;

		case MEM_SEEK_CUR:
			newpos = (int) (stream->position + position);
			break;
			
		case MEM_SEEK_END:
			newpos = (int) (stream->buflen + position);
			break;
		default:
			return -1;
	}

	if (newpos < stream->buflen)
	{
		stream->position = newpos;
		return 0;
	}
	else
	{
		printf("Error seeking to %u\n", newpos);
		return -1;
	}
}