From: Dmitry Selyutin <ghostmansd@gmail.com>
Date: Thu, 27 Oct 2022 16:49:00 +0000 (+0300)
Subject: bitmanip: sync shadd/shadduw pseudocode
X-Git-Tag: opf_rfc_ls001_v3~20
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=767d19e3a7bfae5259e7e06f59fce58a0e24eca6;p=libreriscv.git

bitmanip: sync shadd/shadduw pseudocode
---

diff --git a/openpower/sv/bitmanip.mdwn b/openpower/sv/bitmanip.mdwn
index 5ad241f3f..dae0121a5 100644
--- a/openpower/sv/bitmanip.mdwn
+++ b/openpower/sv/bitmanip.mdwn
@@ -264,16 +264,15 @@ Replaces a pair of explicit instructions in hot-loops.
 
 Pseudo-code (shadd):
 
-    shift <- shift + 1			# Shift is between 1-4
-    sum[0:63] <- ((RB) << shift) + (RA) # Shift RB, add RA
-    RT <- sum				# Result stored in RT
+    n <- (RB)
+    m <- sm + 1
+    RT <- (n[m:XLEN-1] || [0]*m) + (RA)
 
 Pseudo-code (shadduw):
 
-    shift <- shift + 1			# Shift is between 1-4
-    n <- (RB)[XLEN/2:XLEN-1] 		# Limit RB to upper word (32-bits)
-    sum[0:63] <- (n << shift) + (RA)    # Shift n, add RA
-    RT <- sum				# Result stored in RT
+    n <- ([0]*(XLEN/2)) || (RB)[XLEN/2:XLEN-1]
+    m <- sm + 1
+    RT <- (n[m:XLEN-1] || [0]*m) + (RA)
 
 ```
 uint_xlen_t shadd(uint_xlen_t RA, uint_xlen_t RB, uint8_t sm) {