>>     eth_length = ((UI)workbuff[3] << 8) + (UI)workbuff[2];
>>
>>     eth_length = ((UI)workbuff[3] * 256) + (UI)workbuff[2];> That code should only take 4 instructions. How many instructions do
> Hitech and CCS take?

CCS compiles to 11 instructions (this is for an 18C452):
(note that an 'int' in CCS is 8 bits; an 'int16' and a 'long' are
 16 bits - I like the designation with the number of bits in it)

  typedef unsigned int16 UI;

  unsigned int16 eth_length;
  char workbuff[10];

  eth_length = ((UI)workbuff[3] << 8) + (UI)workbuff[2];
    CLRF   6D
    MOVFF  65,6C
    MOVFF  6C,6F
    CLRF   6E
    CLRF   03
    MOVF   64,W
    ADDWF  6E,W
    MOVWF  60
    MOVF   03,W
    ADDWFC 6F,W
    MOVWF  61

   with the variables assigned as follows by the compiler:
     eth_length:  60-61
     workbuff:    62-6B
     compiler scratch:  03, 6C-6F

Both of the above statements compile identically.

Of course, if I were pressed for code size, I would further eschew
portability and use CCS's VERY handy #byte directive:

  unsigned int16 eth_length;
  #byte          eth_lo = eth_length
  #byte          eth_hi = eth_length + 1

  char workbuff[10];

  // eth_length = ((UI)workbuff[3] << 8) + (UI)workbuff[2];
  // is the same as:
  eth_lo = workbuff[2];
  eth_hi = workbuff[3];

  which compiles to 2 instructions:

  MOVFF  64,60
  MOVFF  65,61

Since this takes advantage of the movff instruction in the 18, I checked
all of the above with a 16F876 (which means an older version of CCS's
compiler - 2.708 - instead of v3.053 used for the 18 series stuff - so
I don't know if that's a 'fair' comparison):

eth_length = ((UI)workbuff[3] << 8) + (UI)workbuff[2];   15 instructions
eth_length = ((UI)workbuff[3] * 256) + (UI)workbuff[2];  47 instructions!
with #byte's:  4 instructions

this is with these instructions as the only ones being compiled, which
optimizes bank switching.  For the 18 series, I just tossed these
statements into the middle of a larger project I'm working on - when I
did that with the 16 series, there were bsf 3,6 and bcf 3,6 scattered
throughout.
Just goes to show it ALWAYS pays to look at the code the compiler is
generating - just directing the compiler where to put variables can have
an effect on non-18 code.

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