A few fun things you can do with C structures: 1. Bitfields

struct {
    uint32_t    year        : 7,
                    month    : 4,
                    day        : 5,
                            : 5,
                    hour    : 5,
                    min        : 6;
} compact_date;

Notes: 1. Turns out that C99 defines fixes-size integer types: no more need to define them yourself. 2. The order in which bits are placed into a bitfield (MSB or LSB first) is not standardised - which is ok if you're only on a single platform, but may get messy otherwise. 3. To leave reserved blank spaces, just leave them blank. 4. If you need fewer bits, just use fewer. This structure can store a date (up to 127 years) using only 4 bytes (as opposed to the naive implementation which would require 5 or more). Not a massive win, but convenient when alignment is a concern. 2. Unions

union {
    uint16_t    isDate        : 1,
                    month    : 4,
                    day        : 5;
    uint16_t                : 1,
                    hour    : 5,
                    min        : 6;
} datetime;

This little beauty allows overlapping bitfield definitions: depending on the value of isDate, you can access either month/day or hour:min inside the same compact storage area. 3. Head and trailer structures

struct {
    uint16_t    type;
    uint16_t    len;
    uint8_t        data[1];
} tlv;

This is a fairly common construct but still rather useful. Because C doesn't check array bounds, you can readily access additional data[] elements - the only trick becomes handling sizeof() operations cleanly. To get the size of the header (only):

&((tlv*)0)->data)

To get the size of the complete structure:

sizeof(tlv) + sizeof(tlv.data[0]) * (data_count - 1)

4. And finally, just for fun:

#define STDIO "stdio.h"
#define STRING 
#include STDIO
#include STRING

int main (int argc, char** argv) {
  printf("Don't let me catch you doing this!\n");
}

For our Big-Eye project (a 3.1 Megapixel network camera for security and remote monitoring applications), we needed an efficient software algorithm for converting the Bayer-format data used by the image sensor to RGB data suitable for sending across the network / JPEG compression. A simple C algorithm was coded which did the job. However, it was very slow - about 1.7 seconds to convert a single frame. This was using GCC 4.1.1. The code was fairly well written, using word operations to move through the three lines of the image, two pixels at a time. It was not looking good. After spending a bit of time trying a few basic optimisation techniques, we decided to try the RealView compiler. This now supports most of the GNU options and it is fairly easy to build software using it. The result was pretty astounding. With no code changes, RealView produced an execution time of around 0.3 seconds! A bit of additional fiddling suggested that further improvements might be possible. The main difference seems to be that RealView makes much better use of registers, and thus needs a lot less load/store on the stack. This is probably a common feature of many image processing algorithms. If written with efficiency in mind, they will push the register set quite hard. Much assembler optimisation relies on using the register set more efficiently. But if the compiler can do it for you, so much the better. We could easily have spent a few days working on this part of the code, and with RealView it was just a re-compile. In the end we have moved all the code over to RealView and this is now the standard build environment.

Bluewater Systems participated in a project called Sky Challenge which allows high performance aerobatic aircraft to race through virtual courses.  Using high precision GPS and inertial systems the aircraft's position is sent to a heads up display, which displays a series of objects for the pilot to fly through.  Spectators on the ground were able to watch the actual race in the sky, and a real time computer enhanced version which showed the virtual objects. Bluewater Systems' part in the project was the development of a heads-up display system which the pilot used for flying the course , and co-development of a microwave communication link which sends the positional data for the aircraft to the ground.  The heads-up display software was developed by working closely with a number of aerobatic pilots.  The main goals of the software were to provide the pilots with as much information as possible, without cluttering up the screen. Since Sky Challenge was open to an invite-only audience, have a look at what we were able to experience firsthand. http://news.bbc.co.uk/2/hi/technology/7651500.stm