From: lkcl <lkcl@web>
Date: Thu, 21 Apr 2022 12:13:17 +0000 (+0100)
Subject: (no commit message)
X-Git-Tag: opf_rfc_ls005_v1~2650
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=55d0436835a028b179cb45cb52d36ee7b05f346c;p=libreriscv.git

---

diff --git a/openpower/sv/biginteger/analysis.mdwn b/openpower/sv/biginteger/analysis.mdwn
index 1be393b7c..be9303194 100644
--- a/openpower/sv/biginteger/analysis.mdwn
+++ b/openpower/sv/biginteger/analysis.mdwn
@@ -50,7 +50,28 @@ If there is pressure on the register file (multi-million-digit big integers)
 then a partial-sum may be carried out with LD and ST in a standard
 Cray-style Vector Loop:
 
-   
+    aptr = A address
+    bptr = B address
+    rptr = Result address
+    li r0, 0        # used to help clear CA
+    addic r0, r0, 0 # CA to zero as well
+    setmvli 8       # set MAXVL to 8
+    loop:
+      setvl t0, n         # n is the number of digits
+      mulli t1, t0, 8     # 8 bytes per element
+      sv.ldu a0, aptr, t1 # update advances pointer
+      sv.ldu b0, bptr, t1 # likewise
+      sv.adde r0, a0, b0  # partial, of length VL
+      sv.stu rptr, r0, t1 # pointer advances too
+      sub. n, n, t0       # should not alter CA
+      bnz loop            # do more digits
+
+This is not that different from a Scalar Big-Int add, it is
+just that like all Cray-style Vectorisation, a variable number
+of elements are covered by one instruction.  Of interest
+to people unfamiliar with Cray-style Vectors: if VL is not
+permitted to exceed 1 (MAXVL set to 1) then the above
+actually becomes a Scalar Big-Int add algorithm.
 
 # Multiply