From a7e59e7d4fb06a33c0dcb4d5c5aed0fffedac796 Mon Sep 17 00:00:00 2001
From: Robert Norton
Date: Tue, 7 Jun 2016 12:53:27 +0100
Subject: cheri: implement the csub instruciton (new instruction)

---
 cheri/cheri_insts.sail | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/cheri/cheri_insts.sail b/cheri/cheri_insts.sail
index 71f76170..d3d84a53 100644
--- a/cheri/cheri_insts.sail
+++ b/cheri/cheri_insts.sail
@@ -178,6 +178,23 @@ function clause execute(CToPtr(rd, cb, ct)) =
     }
 }
 
+union ast member regregreg CSub
+function clause decode (0b010010 : 0b00000 : (regno) rd : (regno) cb : (regno) ct : 0b001010) = Some(CSub(rd, cb, ct))
+function clause execute(CSub(rd, cb, ct)) = 
+{
+  checkCP2usable();
+  ct_val := readCapReg(ct);
+  cb_val := readCapReg(cb);
+  if (register_inaccessible(cb)) then
+    exit (raise_c2_exception_v(cb))
+  else if (register_inaccessible(ct)) then
+    exit (raise_c2_exception_v(ct))
+  else 
+    {
+      wGPR(rd) := (bit[64])(getCapCursor(cb_val) - getCapCursor(ct_val))
+    }
+}
+
 union ast member (regno, regno, regno, CPtrCmpOp) CPtrCmp
 function clause decode (0b010010 : 0b01110 : (regno) rd : (regno) cb : (regno) ct : 0b000 : 0b000) = Some(CPtrCmp(rd, cb, ct, CEQ))
 function clause decode (0b010010 : 0b01110 : (regno) rd : (regno) cb : (regno) ct : 0b000 : 0b001) = Some(CPtrCmp(rd, cb, ct, CNE))
-- 
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