From: Andrey Miroshnikov <andrey@technepisteme.xyz>
Date: Mon, 24 Oct 2022 12:24:49 +0000 (+0100)
Subject: bitmanip: Adding draft pseudo-code for shadd and shadduw
X-Git-Tag: opf_rfc_ls005_v1~46
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=1fed7949ef5dba45b1a3c378137a3fecb57aa7bf;p=libreriscv.git

bitmanip: Adding draft pseudo-code for shadd and shadduw
---

diff --git a/openpower/sv/bitmanip.mdwn b/openpower/sv/bitmanip.mdwn
index 1f91d90d3..11bf89447 100644
--- a/openpower/sv/bitmanip.mdwn
+++ b/openpower/sv/bitmanip.mdwn
@@ -249,6 +249,24 @@ Replaces a pair of explicit instructions in hot-loops.
     | PO   |  RT  |   RA     |   RB  |sm |   XO |Rc |
 ```
 
+```
+Pseudo-code (shadd):
+    shift <- sm & 0x3			# Ensure sm is 2-bit
+    shift <- shift + 1			# Shift is between 1-4
+    sum[0:63] <- ((RB) << shift) + (RA) # Shift RB, add RA
+    RT <- sum				# Result stored in RT
+```
+
+Is Rc used to indicate the two modes?
+```
+Pseudo-code (shadduw):
+    shift <- sm & 0x3			# Ensure sm is 2-bit
+    shift <- shift + 1			# Shift is between 1-4
+    n <- (RB) & 0xFFFFFFFF		# Limit RB to upper word (32-bits)
+    sum[0:63] <- (n << shift) + (RA)    # Shift n, add RA
+    RT <- sum				# Result stored in RT
+```
+
 ```
 uint_xlen_t shadd(uint_xlen_t RA, uint_xlen_t RB, uint8_t sm) {
     sm = sm & 0x3;