From 54ea34d560dc9db9b1a6280f453c4dcd9879ec6d Mon Sep 17 00:00:00 2001
From: Mikael Pettersson <mikpelinux@gmail.com>
Date: Tue, 8 May 2018 22:39:18 +0200
Subject: [PATCH] pdp10-arith: add pdp10_sext_uint18()

---
 include/pdp10-arith.h | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/include/pdp10-arith.h b/include/pdp10-arith.h
index cf5caa5..e1823d8 100644
--- a/include/pdp10-arith.h
+++ b/include/pdp10-arith.h
@@ -1,6 +1,6 @@
 /*
  * pdp10-arith.h -- arithmetic on PDP10 integer types
- * Copyright (C) 2013-2015  Mikael Pettersson
+ * Copyright (C) 2013-2018  Mikael Pettersson
  *
  * This file is part of pdp10-tools.
  *
@@ -44,6 +44,14 @@ static inline pdp10_int36_t pdp10_sext_int36(pdp10_uint36_t x)
     return ((x & PDP10_UINT36_MAX) ^ PDP10_UINT36_SBIT) - PDP10_UINT36_SBIT;
 }
 
+/* Sign-extend a pdp10_uint18_t to the full width of its representation type. */
+static inline pdp10_uint18_t pdp10_sext_uint18(pdp10_uint18_t x)
+{
+    const pdp10_uint18_t PDP10_UINT18_SBIT = ~(PDP10_UINT18_MAX >> 1) & PDP10_UINT18_MAX;
+
+    return ((x & PDP10_UINT18_MAX) ^ PDP10_UINT18_SBIT) - PDP10_UINT18_SBIT;
+}
+
 static inline pdp10_uint36_t pdp10_neg_int36(pdp10_uint36_t x)
 {
     return pdp10_zext_uint36(-pdp10_sext_int36(x));