From: Andrey Miroshnikov <andrey@technepisteme.xyz>
Date: Fri, 28 Oct 2022 22:30:43 +0000 (+0100)
Subject: ls003: Started adding dsrd
X-Git-Tag: opf_rfc_ls005_v1~29
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=e39a7ae9fe9d66d75cfb1ce6be72c1619f48bb84;p=libreriscv.git

ls003: Started adding dsrd
---

diff --git a/openpower/sv/rfc/ls003.mdwn b/openpower/sv/rfc/ls003.mdwn
index 8a6e70a59..1bcb0fb2d 100644
--- a/openpower/sv/rfc/ls003.mdwn
+++ b/openpower/sv/rfc/ls003.mdwn
@@ -263,15 +263,17 @@ Pseudo-code:
     v <- ROTL64((RA), n)                    # Rotate RA 64-bit left by n bits
     mask <- MASK(64, 63-n)                  # 1's mask, set mask[64-n:63] to 0's
     RT <- (v[0:63] & mask) | ((RC) & ¬mask) # Mask out bits
-    RS <- v[0:63] & ¬mask
-    overflow = 0
-    if RS != [0]*64:
-        overflow = 1
+    RS <- v[0:63] & ¬mask                   # ?
+    overflow = 0                            # Clear overflow flag
+    if RS != [0]*64:                        # Check if RS is NOT zero
+        overflow = 1                        # Set the overflow flag
 
 Special Registers Altered:
 
     CR0                    (if Rc=1)
 
+**CHECK if overflow flag is the expected behaviour**
+
 The contents of register RA are shifted left the number
 of bits specified by (RB) 58:63.
 **Please check if this is correct!!! This condition is taken
@@ -289,6 +291,29 @@ overflow flag is raised.
 
 Similarly maddedu and divmod2du, dsld can be chained (using RC).
 
+# Dynamic-Shift Right Doubleword
+
+`dsrd RT,RA,RB,RC`
+
+|  0-5  | 6-10 | 11-15 | 16-20 | 21-25 | 26-30 | 31 | Form     |
+|-------|------|-------|-------|-------|-------|----|----------|
+| EXT04 | RT   |  RA   |  RB   |   RC  |  XO   | Rc | VA2-Form |
+
+Pseudo-code:
+
+    n <- (RB)[58:63]                        # Take lower 6-bits of RB for shift
+    v <- ROTL64((RA), 64-n)                 # Rotate RA 64-bit left by 64-n bits
+    mask <- MASK(n, 63)                     # 0's mask, set mask[n:63] to 1' 
+    RT <- (v[0:63] & mask) | ((RC) & ¬mask) # 
+    RS <- v[0:63] & ¬mask
+    overflow = 0
+    if RS != [0]*64:
+        overflow = 1
+
+Special Registers Altered:
+
+    CR0                    (if Rc=1)
+
 
 \newpage{}