Re: Why VAX Was the Ultimate CISC and Not RISC

On 2025-03-07 12:34 p.m., MitchAlsup1 wrote:

On Fri, 7 Mar 2025 11:08:56 +0000, BGB wrote:
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On 3/6/2025 10:09 PM, Lawrence D'Oliveiro wrote:

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So, writing things like:
   y[55:48]=x[19:12];

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2 instructions in My 66000. One extract, one insert.

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Ibid for Q+. The logic for an extract and insert as one operation might
add to the timing. Extract, sign/zero extend and copy back. Fields may
be different sizes.
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And:
   j=x[19:12];
Also a single instruction, or 2 or 3 in the fallback case (encoded as a
shift and mask).

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1 instruction--extract (SLL or SLA)

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Q+ has EXT/EXTU which is basically a SRL or SRA with mask applied
afterwards. PowerPC has a rotate-left-and-mask instruction. In my
opinion it makes more sense for extracts to be shifting right.