The dive sample structure

[Willem Ferguson]

Here is a consensus structure after correcting my miscalculations and 
taking the comments of Linus and Thiago. Without using uint16 or uint8 
integers in some variables, the size of sample would be 64 bytes. By 
using fixed-width variables in some places the size is 48 bytes. I 
reckon this is meant as a compromise proposal that tries to conserve 
memory space but still maintains flexibility. Just to give a thumbsuck 
of the RAM implications of the size of sample: If there is a maniacal 
commercial diver out there who does 1000 dives of 5h (rebreather), the 
size of his/her dive log file could be in the order of 250 Mbytes in RAM 
(18000 samples/dive at a dive computer sampling rate around every 3 
seconds for a rebreather, resulting in some Tbytes of xml on disk ). 
Without fixed-length variables, RAM utilisation would be towards 350 
Mbytes.

Changes to the composition of the sample structure needs to be a 
consultative decision because it is likely to influence many individuals 
coding Subsurface. Please look carefiully at the typedefs and structure. 
I hope there are not any remaining miscalculations.

1) Should one use the fixed-width integers (uint8 and uint16)?

2) If so, do the fixed-with fields have enough span for what could be 
encountered in real dives?

As usual, I attach a PDF version of the code snippet.

typedef struct        //unchanged depth_t
{
     int mm;
} depth_t;

typedef struct        // unchanged duration_t
{
     int seconds;
} duration_t;

typedef struct        // unchanged pressure_t
{
     int mbar;
} pressure_t;

typedef struct        // unchanged temperature_t
{
     int mkelvin;
} temperature_t;

typedef struct        // new type definition; type uint16_t  shortduration_t
{
     uint16_t seconds;
} shortduration_t;

typedef struct        // new type definition; type uint16_t  o2pressure_t
{
     uint16_t mbar;
} o2pressure_t;

typedef struct        // new type definition; type int16_t bearing_t
{
     int16_t degrees;
} bearing_t;

struct sample {                //TYPE        UNITS RANGE         BYTES
     duration_t time;           //int        seconds (0-68yrs)       4
     shortduration_t stoptime;  //uint16_t    seconds (0-18h)         2
     shortduration_t ndl;      //uint16_t    seconds (0-18h)         2
     depth_t depth;            //int          mm (0-2000km)      4
     depth_t stopdepth;        //int          mm (0-2000km)      4
     temperature_t temperature;//int         mdegrK (0-2MdegrK)     4
     pressure_t cylinderpressure; //int       mbar (0-2Mbar)      4
     pressure_t sensor;        //int          mbar (0-2Mbar)      4
     pressure_t pdiluent;      //int          mbar (0-2Mbar)      4
     o2pressure_t po2;         //uint16_t     mbar (0-65 bar)     2
     o2pressure o2sensor[3];   //uint16_t     mbar (0-65 bar)     6
     o2pressure setpoint       //uint16_t     mbar (0-65 bar)     2
     bearing_t bearing;        //int16_t     degrees (-32k - 32kdegr)2
     uint8_t cns;              //uint8_t       % (0-255%)       1
     unint8_t heartbeat;       //uint8_t     beats/s (0-256)       1
     bool in_deco;             //bool         y/n --          1
};
                                 Total size    47 bytes
                                 (+1 byte for filling to 48?)
                                 ( = next word boundary?)
Kind regards,
willem






-------------- next part --------------
A non-text attachment was scrubbed...
Name: sample_structure_24Apr.pdf
Type: image/pdf
Size: 17338 bytes
Desc: not available
URL: <http://lists.hohndel.org/pipermail/subsurface/attachments/20140424/6a90c583/attachment.bin>