Re: Bit swizzling

gah4 <>
Thu, 10 Sep 2020 10:34:18 -0700 (PDT)

          From comp.compilers

Related articles
[4 earlier articles]
Re: Bit swizzling ( (2020-09-06)
Re: Bit Swizzling (Chris) (2020-09-06)
Re: Bit swizzling (Martin Ward) (2020-09-07)
Re: Bit swizzling (Rick C. Hodgin) (2020-09-07)
Re: Bit swizzling (Hans-Peter Diettrich) (2020-09-08)
Re: Bit swizzling (Tom Crick) (2020-09-08)
Re: Bit swizzling (gah4) (2020-09-10)
Re: Bit swizzling (Rick C. Hodgin) (2020-09-10)
| List of all articles for this month |

From: gah4 <>
Newsgroups: comp.compilers
Date: Thu, 10 Sep 2020 10:34:18 -0700 (PDT)
Organization: Compilers Central
References: 20-09-014
Injection-Info:; posting-host=""; logging-data="67222"; mail-complaints-to=""
Keywords: optimize, hardware
Posted-Date: 10 Sep 2020 13:55:01 EDT
In-Reply-To: 20-09-014

On Saturday, September 5, 2020 at 9:45:43 AM UTC-7, Rick C. Hodgin wrote:
> Are there any algorithms which take a known-at-compile-time sequence
> of bitwise operations on an 8-bit to 64-bit quantity, and optimize
> them down to their minimal set of operations?
> For example, if I have an 8-bit byte and I want to swizzle the bits
> thusly:
> Input: 07 06 05 04 03 02 01 00
> Output: 05 04 07 02 01 03 00 06

There is a lot of work, and many algorithms, for logic optimization,
or minimization, that, for example, will find the optimal combination
of NAND and NOR gates to evaluate some logical operation.

This is used to compile Verilog or VHDL into either FPGA bit files
or ASIC masks. On the other hand, logic minimization tends to
believe that you can wire anything to anything else. That is, bit
swizzle is just wiring. The question you ask doesn't come up.
(Later on, routing has to get all the wires to the appropriate
place, but that is true in general, not just for this case.)

Note that it isn't just adjacent bits, but bits with the same spacing
in the input and output, such that you can mask with AND, shift,
and combine with OR. I suspect that with the operations usually
available: AND, OR, XOR, and shift, it wouldn't be hard to find an
algorithm for the optimal case. If you add more operations,
maybe allow also add and multiply, it gets interesting.

Post a followup to this message

Return to the comp.compilers page.
Search the comp.compilers archives again.