From 46a84e1f16f1f9670120a71b8dbbc7492a992595 Mon Sep 17 00:00:00 2001
From: lkcl <lkcl@web>
Date: Thu, 21 Apr 2022 09:34:43 +0100
Subject: [PATCH]

---
 openpower/sv/biginteger/analysis.mdwn | 28 +++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/openpower/sv/biginteger/analysis.mdwn b/openpower/sv/biginteger/analysis.mdwn
index cd2e3bd61..ce4898372 100644
--- a/openpower/sv/biginteger/analysis.mdwn
+++ b/openpower/sv/biginteger/analysis.mdwn
@@ -4,6 +4,12 @@ This section covers an analysis of big integer operations.  Use of
 smaller sub-operations is a given: worst-case, addition is O(N)
 whilst multiply and divide are O(N^2).
 
+Links
+
+* <http://www.intel.com/content/dam/www/public/us/en/documents/white-papers/ia-large-integer-arithmetic-paper.pdf>
+* <https://lists.libre-soc.org/pipermail/libre-soc-dev/2022-April/004700.html>
+* <https://news.ycombinator.com/item?id=21151646>
+
 # Add and Subtract
 
 Surprisingly, no new additional instructions are required to perform
@@ -69,6 +75,28 @@ to multiply, and an additional accumulator (C). However if
 C is left out (and added afterwards with a Vector-Add)
 things become more manageable.
 
+Demonstrating in c, a Row-based multiply using a temporary vector.
+Adapted from a simple implementation
+of Knuth M: <https://git.libre-soc.org/?p=libreriscv.git;a=blob;f=openpower/sv/bitmanip/mulmnu.c;hb=HEAD>
+
+```
+      // this becomes the basis for sv.madded in RS=RC Mode,
+      // where k is RC
+      k = 0;
+      for (i = 0; i < m; i++) {
+         unsigned product = u[i]*v[j] + k;
+         k = product>>16;
+         plo[i] = product; // & 0xffff
+      }
+      // this is simply sv.adde where k is XER.CA
+      k = 0;
+      for (i = 0; i < m; i++) {
+         t = plo[i] + w[i + j] + k;
+         w[i + j] = t;          // (I.e., t & 0xFFFF).
+         k = t >> 16; // carry: should only be 1 bit
+      }
+```
+
 We therefore propose an operation that is 3-in, 2-out,
 that, noting that the connection between successive
 mul-adds has the UPPER half of the previous operation
-- 
2.30.2