From: lkcl <lkcl@web>
Date: Tue, 21 Nov 2023 11:47:39 +0000 (+0000)
Subject: (no commit message)
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=b70996ee14eeb644a69295c2de08d712c845caee;p=libreriscv.git

---

diff --git a/openpower/sv/cookbook/pospopcnt.mdwn b/openpower/sv/cookbook/pospopcnt.mdwn
index d28897169..d350ffae7 100644
--- a/openpower/sv/cookbook/pospopcnt.mdwn
+++ b/openpower/sv/cookbook/pospopcnt.mdwn
@@ -1,6 +1,17 @@
-<https://bugs.libre-soc.org/show_bug.cgi?id=672>
+# Positional popcount SVP64
+
+* <https://bugs.libre-soc.org/show_bug.cgi?id=672>
+* <https://github.com/clausecker/pospop/blob/master/countsse2_amd64.s>
+
+Positional popcount in optimised assembler is typically done on SIMD ISAs in
+around 500 lines.  Power ISA thanks to `bpermd` can be much more efficient:
+with SVP64 even more so.  The reference implementation showing the concept
+is below, and it adds up the totals of each bit set to 1 in each bit-position,
+of an array of input alues.
 
 ```
+// Copyright (c) 2020 Robert Clausecker <fuz@fuz.su>
+// count8 reference implementation for tests.  Do not alter.
 func count8safe(counts *[8]int, buf []uint8) {
 	for i := range buf {
 		for j := 0; j < 8; j++ {
@@ -8,14 +19,6 @@ func count8safe(counts *[8]int, buf []uint8) {
 		}
 	}
 }
-
-func count16safe(counts *[16]int, buf []uint16) {
-	for i := range buf {
-		for j := 0; j < 16; j++ {
-			counts[j] += int(buf[i] >> j & 1)
-		}
-	}
-}
 ```
 
 [[!tag svp64_cookbook ]]