From: Luke Kenneth Casson Leighton <lkcl@lkcl.net>
Date: Tue, 9 Jan 2024 10:59:37 +0000 (+0000)
Subject: bug 1244: describe ddffirst details
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=e0cc6cc03613da1638cd60193c2a9ce8d5e5b4b2;p=libreriscv.git

bug 1244: describe ddffirst details
---

diff --git a/conferences/fosdem2024/fosdem2024_ddffirst/fosdem2024_ddffirst.tex b/conferences/fosdem2024/fosdem2024_ddffirst/fosdem2024_ddffirst.tex
index c739b4377..06a73fe60 100644
--- a/conferences/fosdem2024/fosdem2024_ddffirst/fosdem2024_ddffirst.tex
+++ b/conferences/fosdem2024/fosdem2024_ddffirst/fosdem2024_ddffirst.tex
@@ -130,24 +130,6 @@ function op\_cmpi(BA, RA, SI) # cmpi not vector-cmpi!
 \end{frame}
 
 
-
-\begin{frame}[fragile]
-\frametitle{Data-Dependent-Fail-First in a nutshell}
-
-\begin{semiverbatim}
-	while srcstep < VL - 1
-		RT[SS], Rc = DO (MAXS, RA[SS], RB)
-		if test (Rc) == FAIL: VL = srcstep + 1, break	
-	
-\end{semiverbatim}
-
-\begin{itemize}
-	\item Above is oversimplified: predication etc. left out
-	\item Scalar-scalar and scalar-vector and vector-vector now all in one
-	\item OoO may choose to push CMPIs into instr. queue (v. busy!)
-\end{itemize}
-\end{frame}
-
 \frame{\frametitle{Load/Store Fault-First}
 	
 	\begin{itemize}
@@ -164,6 +146,30 @@ function op\_cmpi(BA, RA, SI) # cmpi not vector-cmpi!
 	\end{itemize}
 }
 
+\begin{frame}[fragile]
+	\frametitle{Data-Dependent-Fail-First in a nutshell}
+	
+	\begin{semiverbatim}
+function op\_cmpi(BA, RA, SI) # cmpi not vector-cmpi!
+int i, id=0, ira=0;
+for (i = 0; i < VL; i++)
+    CR[BA+id] <= compare(ireg[RA+ira], SI);
+    if (reg\_is\_vectorised[BA] ) \{ id += 1; \}
+    if (reg\_is\_vectorised[RA])  \{ ira += 1; \}
+    if test (CR[BA+id]) == FAIL: \{ VL = id + 1; break \}
+	\end{semiverbatim}
+	
+	\begin{itemize}
+		\item Parallelism still perfectly possible
+		      ("hold" writing results until sequential post-analysis
+		       carried out. Best done with OoO)
+		\item VL truncation can be inclusive or exclusive
+		      (include or exclude a NULL pointer or a
+		      string-end character, or overflow result)
+		\item 
+	\end{itemize}
+\end{frame}
+
 
 
 \frame{\frametitle{Additional Simple-V features}