Compressed-format-27-apr-2013

Hi,

To get the ball rolling, below I describe what I do to drop our MC event size by approximately a factor of 3.  
Currently we only generate data for FADC250, FADC125, F1TDC32 and F1TDC48 modules, and for the ADC's only in "pulse integral" mode.
I know nothing about other modules or other readout modes.  I currently only deal with disentangled events.

Starting with mc2coda output:

1.  ignore all filler words.
2.  remove module if it has no hit data
3.  remove crate if it has no hit data in any module.

For modules with hit data:

1.  replace 4 words overhead per module (block header, event header, trigger time, block trailer) with a single leading word
encoding info from header/trailer words, as well as tHE number of hits for this module.  I encode the single header word as below,
the unchanged data words follow the header word:

>             *iter3=0xe0000000;                     // 5 bits slot header
>               (*iter3)|=(slot&0x1f)<<22;         // 5 bits slot number
>               (*iter3)|=(type&0xf) <<18;        // 4 bits module type
>               (*iter3)|=nhitwords&0xffff;         // 16 bits hit count (could be smaller)

2.  store trigger time once-only in a header bank at the beginning of the event.