Re: Why VAX Was the Ultimate CISC and Not RISC

On Fri, 7 Mar 2025 22:25:12 +0000, Scott Lurndal wrote:

mitchalsup@aol.com (MitchAlsup1) writes:

On Fri, 7 Mar 2025 11:08:56 +0000, BGB wrote:
>

For a simple test:
   lj[ 7: 0]=li[31:24];
   lj[15: 8]=li[23:16];
   lj[23:16]=li[15: 8];
   lj[31:24]=li[ 7: 0];
Does seem to compile down to 4 instructions.

>
1 innstruction:: BITR rd,rs1,<8>

>
Isn't that just 'bswap32' on x86, or REV32 on ARM64?

A degenerate version is:: but consider::
       BITR Rd,Rs1,<1>
performs bit reversion, while::
       BITR Rd,Rs1,<2>
reverses pairs of bits, ...
       BITR  Rs,Rs1,<16>
reverses halfwords.