XPost: comp.lang.c, comp.arch.fpga   
   From: address@nospicedham.not.available   
      
   (Too many xpost groups, had to remove one)   
      
   Rick,   
      
   >         o |= (((v & (1 << s)) >> s) << d);   
      
   If you reverse the two tables (having the output bits in order from high to   
   low) you could left-shift the output by one and than OR the output with the   
   right-shifted input masked with 1.   In this specific case (all eight bits   
   swizzeled) you do not even need to clear the output.   
      
   My C(++) isn't worth anything, but I imagine it could look something like   
   this :   
      
   o <<= 1   
   o |=  (v >> s) & 1   
      
   That takes, at least on a x86, 4 machine instructions per bit.   
      
   The thing with writing C(++) that should work /everywhere/ is that you can't   
   use optimalisations for a specific processor.   
      
   If you would use the x86, which has instructions that use the Carry flag as   
   the ninth bit, you would only need 2 machine instructions per bit (rotate   
   desired source bit into carry, rotate carry bit into target).   
      
   And a remark : you've made that "swizzle" a function.  Which means you will   
   probably have a relative large overhead, possibly doubling if not tripling   
   the ammount of instructions executed for each bit extraction and insertion   
   (starting with the "call" and "return").   Rewiting it as a macro would   
   probably be a good idea.   
      
   In the case of an x86 and some smart-ass usage of its nine-bit rotate   
   instructions means that a full 8 bit swizzle uses only 16 instructions (or   
   17 if you want the source to be unchanged afterwards) - both code /and/   
   execution ...   
      
   Regards,   
   Rudy Wieser   
      
   --- SoupGate-Win32 v1.05   
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