From 06676bea51e3ec2e2d5b1204c04a1e8571e7008c Mon Sep 17 00:00:00 2001 From: lkcl Date: Tue, 19 Apr 2022 19:34:46 +0100 Subject: [PATCH] --- openpower/sv/biginteger.mdwn | 21 +++++++++++++++++++++ 1 file changed, 21 insertions(+) diff --git a/openpower/sv/biginteger.mdwn b/openpower/sv/biginteger.mdwn index ac271714b..27d6981e8 100644 --- a/openpower/sv/biginteger.mdwn +++ b/openpower/sv/biginteger.mdwn @@ -103,6 +103,27 @@ that, just as with repeated chained application of `addeo`, macro-op fusion may be internally applied to a sequence of these strange multiply operations. Such a trick works equally as well in Scalar-only. +**Application of SVP64** + +SVP64 has the means to re-target in-out registers that would normally +be forced to be an overwrite. Examples include `ldu` which, ordinarily, +in Scalar v3.0B, has RA overwritten. `sv.ldu` on the other hand permits +limited range re-targetting, by applying one EXTRA bit to RA-as-a-source +and a *separate* bit to RA-as-a-destination. + +If applied to this new 3-in 2-out mul-and-add operation it not only +becomes possible to set RC as either scalar or vector, it becomes +possible to stop RC from being overwritten. + + product = RA*RB+RC # RC sourced as Vector + RT = lowerhalf(product) # Vector destination + RC = upperhalf(product) # Vector destination + +Where previously this instruction had limited specialist applicability +for big-integer multiply, because RC could only be utilised as a +64-bit Carry, the possibility for RC to be a Vector greatly +expands its potential. + ## Divide The simplest implementation of big-int divide is the standard schoolbook -- 2.30.2