Have you considered storing this in some sort of word-aligned manner...

I.E. let's assume you want to store 500 8 bit bytes...

Store the first 286 as bits 0...7 bits of each word (8 bits).
Store the next 143 as bits 8..11 of each word, but spread across 2 words.
Store the final 71 as bits 12 & 13 of eac word, and spread across 4 words.

Then your algorithm looks like (semi pseudo-code, in c ...  That is, 
don't shoot me if I mangled something like & versus && or >>'d the wrong 
way or too few/too many bits- I've had too long of a day today so I 
might have messed up and I don't feel like looking it up.)

uint8 retrievebyte (uint16 address)
{
  if (address<286)
  {
     return flash[address]&&0xff;
  }
  else if (address<(143+286))
  {
     //return bits 8.11 of address*2 in lower 4 bits, and 8.11 of 
address*2+1 in higher 4 bits;
     return (   (flash[address*2]>>8) && 0x0f) +
                   (flash[address*2+1]>>4&&0xf0)
               );
  }
  else if (address<(71+143+286))
  {
     return (   (flash[address*2]>>12) && 0x03) +
                   (flash[address*2+1]>>10&&0x0c) +
                   (flash[address*2+2]>>8&&0x30) +
                   (flash[address*2+3]>>6&&0xc0)
               );

   }
   else
   {
      /// Handle out of range error accordingly.
      return 0;
   }
}


Ed Sutton wrote:
> Are there other ways to implement a divide by a 14 constant other than 
> cycle-chewing subtraction loops?
>
> I want to use the PIC16F flash consisting of 14-bit words to store 8-bit 
> data.  I can implement the multiply-by-8 as a shift.  The crux of the 
> problem is basically the divide by a constant of 14.
>
> Pseudo Code ( actual code will likely be assembly )
>
> wordOffset = 8*byteOffset / 14;          // The integer result 
> wordBitOffset = 8*byteOffset % 14;   // The remainder result
>
>
> Patterns:
>
> The 14-bit words and 8-bit data have a common multiple of 56.
> The wordBitOffset pattern { 0,8,2,10,4,12,6 } repeats every 7-bytes.
> I can't see a solution but it is an interesting puzzle.
>
> Thanks in advance for any tips or suggestions,
>
> -Ed
>
>   

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