3 ms·

Certainly the BCD instructions are not used?

• dbcurtis 10y ago
  Well, be sure to check out a COBOL compiler before you write it off. But it's certainly rare. BCD arithmetic is an artifact of history. The 4004 was targeting desktop calculators. And IIRC all of the microprocessors in the 8008/8080 era had some support for BCD.
• dragonwriter 10y ago
  IIRC, Turbo Pascal and its descendants (including Delphi and FreePascal) have support BCD arithmetic at the language level (but it might be part of stdlib), so I'd imagine that either the compiler outputs BCD instructions or BCD instructions are inlined in the library implementation. EDIT: Although its possible that they use something else behind the scenes and just convert to/from BCD representation. That seems intuitively likely to be inefficient, but if keeping BCD ops efficient hasn't been a focus of CPU development, its possibly not the ideal way to do things under the hood, even when at the application language level it is presented as doing BCD.
• krylon 10y ago
  A couple of years back, I did a little (LITTLE! Very superficial!) research into doing BCD on x86, and if my very fuzzy memory of that time is not totally wrong, the BCD support in x86 was never all that great. Certainly nowhere near the support for arithmetic on fixed-sized binary integers. Also, being mostly unused, Intel had little incentive to to make these instructions run fast. So there might be programs somewhere that actually use these instructions, but I would not be surprised if there also were programs that do BCD arithmetic without using the x86 BCD instructions. (Especially if these were written in in a HLL, compiled by a compiler that has no idea what you are trying to do.)