X68000 Game Launcher - #3: Bitmap loader

The header includes these common files:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
 
#include "bmp.h"

The header bmp.h defines bitmap data structures and a function prototypes for the bitmap library:

#include <stdint.h>
 
#define BMP_FILE_SIG_OFFSET	0x0000 // Should always be 'BM'
#define BMP_FILE_SIZE_OFFSET	0x0002 // Size of file, including headers
#define DATA_OFFSET_OFFSET 	0x000A // How many bytes from 0x0000 the data section starts
#define WIDTH_OFFSET 		0x0012 // Where we can find the x-axis pixel size
#define HEIGHT_OFFSET 		0x0016 // Where we can find the y-axis pixel size
#define BITS_PER_PIXEL_OFFSET	0x001C // Where we can find the bits-per-pixel number
#define COMPRESS_OFFSET		0x001E // Where we can find the compression flag
#define COLOUR_NUM_OFFSET	0x002E // Where we can find the numbers of colours used in the image
#define COLOUR_PRI_OFFSET	0x0032 // Where we can find the number of the 'important' colour ???
#define PALETTE_OFFSET		0x0036 // Where the colour palette starts, for <=8bpp images.
#define HEADER_SIZE 		14
#define INFO_HEADER_SIZE 	40
#define BMP_1BPP		1
#define BMP_8BPP		8	
#define BMP_16BPP		16
#define BMP_UNCOMPRESSED	0
#define BMP_VERBOSE		0 // Enable BMP specific debug/verbose output
#define BMP_OK			0 // BMP loaded and decode okay
#define BMP_ERR_NOFILE		-1 // Cannot find file
#define BMP_ERR_SIZE		-2 // Height/Width outside bounds
#define BMP_ERR_MEM		-3 // Unable to allocate memory
#define BMP_ERR_BPP		-4 // Unsupported colour depth/BPP
#define BMP_ERR_READ		-5 // Error reading or seeking within file
#define BMP_ERR_COMPRESSED	-6 // We dont support comrpessed BMP files
#define BMP_ERR_FONT_WIDTH	-7 // We dont support fonts of this width
#define BMP_ERR_FONT_HEIGHT	-8 // We dont support fonts of this height
 
#define BMP_FONT_MAX_WIDTH	8
#define BMP_FONT_MAX_HEIGHT	16
#define BMP_FONT_PLANES		4 // Number of colour planes per pixel
 
 
// ============================
//
// BMP image data structure
//
// ============================
typedef struct bmpdata {
	unsigned int 	width;		// X resolution in pixels
	unsigned int 	height;		// Y resolution in pixels
	char		compressed;     // If the data is compressed or not (usually RLE)
	uint16_t 	bpp;		// Bits per pixel
	uint16_t 	bytespp;	// Bytes per pixel
	uint32_t 	offset;		// Offset from header to data section, in bytes
	unsigned int 	row_padded;	// Size of a row without padding
	unsigned int 	row_unpadded;	// SIze of a row, padded to a multiple of 4 bytes
	unsigned int 	size;		// Size of the pixel data, in bytes
	unsigned int	n_pixels;	// Number of pixels
	uint8_t 	*pixels;	// Pointer to raw pixels - in font mode each byte is a single character
} __attribute__((__packed__)) __attribute__((aligned (2))) bmpdata_t;
 
// ============================
//
// BMP state structure
//
// ============================
typedef struct bmpstate {
	unsigned int	width_bytes;
	unsigned int	rows_remaining;	// Total number of rows left to be read
	uint8_t		*pixels;	// Needs to be malloc'ed to the width of a single row of pixels
} __attribute__((__packed__)) __attribute__((aligned (2))) bmpstate_t;
 
// ============================
//
// Font data structure
//
// 96 characters, 
// each character is 1 byte wide, and up to 16 (max) rows high 
// each row is 4 planes
// total of 6144 bytes per 96 character font
//
//=============================
typedef struct fontdata {
	uint8_t	width;		// Width of each character, in pixels
	uint8_t	height;		// Height of each character, in pixels
	uint8_t	ascii_start;	// ASCII number of symbol 0
	uint8_t	n_symbols;	// Total number of symbols
	uint8_t	unknown_symbol;	// Which symbol do we map to unknown/missing symbols?
	uint8_t symbol[96][BMP_FONT_MAX_HEIGHT][BMP_FONT_PLANES]; 
} __attribute__((__packed__)) __attribute__((aligned (2))) fontdata_t;
 
void	bmp_Destroy(bmpdata_t *bmpdata);
void	bmp_DestroyFont(fontdata_t *fontdata);
int 	bmp_ReadFont(FILE *bmp_image, bmpdata_t *bmpdata, fontdata_t *fontdata, uint8_t header, uint8_t data, uint8_t font_width, uint8_t font_height);
int 	bmp_ReadImage(FILE *bmp_image, bmpdata_t *bmpdata, uint8_t header, uint8_t data);
int 	bmp_ReadImageHeader(FILE *bmp_image, bmpdata_t *bmpdata);
int 	bmp_ReadImageData(FILE *bmp_image, bmpdata_t *bmpdata);

The bitmap library has a single function, bmp_ReadImage(), that is called in several different ways to parse BMP headers, read pixel data