From 6064e4f3b03411b8898804ba4dac389686791c67 Mon Sep 17 00:00:00 2001
From: Chris Sherlock <chris.sherlock79@gmail.com>
Date: Fri, 4 May 2018 03:40:11 +1000
Subject: tools: document and test sanitiseMm100ToTwip()

Change-Id: I2f6349c679a714e5168ae3c5eccd054c5522bbc9
Reviewed-on: https://gerrit.libreoffice.org/53814
Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>
---
 include/tools/helpers.hxx             | 16 ++++++++--
 tools/CppunitTest_tools_test.mk       |  1 +
 tools/qa/cppunit/test_100mm2twips.cxx | 55 +++++++++++++++++++++++++++++++++++
 3 files changed, 70 insertions(+), 2 deletions(-)
 create mode 100644 tools/qa/cppunit/test_100mm2twips.cxx

diff --git a/include/tools/helpers.hxx b/include/tools/helpers.hxx
index 8325f095bad8..0a349ea62d1d 100644
--- a/include/tools/helpers.hxx
+++ b/include/tools/helpers.hxx
@@ -55,7 +55,19 @@ inline long FRound( double fVal )
     return fVal > 0.0 ? static_cast<long>( fVal + 0.5 ) : -static_cast<long>( -fVal + 0.5 );
 }
 
-// return (n >= 0)? (n*72+63)/127: (n*72-63)/127;
+/** Convert 100th-mm to twips
+
+    A twip is 1/20 of a point, one inch is equal to 72 points, and
+    one inch is 2,540 100th-mm.
+
+    Thus:
+        twips = n * 72 / 2,540 / 20
+              = n * 72 / 127
+
+    Adding 63 (half of 127) fixes truncation issues in int arithmetic.
+
+    This formula is (n>=0) ? (n*72+63) / 127 : (n*72-63) / 127
+ */
 inline sal_Int64 sanitiseMm100ToTwip(sal_Int64 n)
 {
     if (n >= 0)
@@ -68,7 +80,7 @@ inline sal_Int64 sanitiseMm100ToTwip(sal_Int64 n)
         if (o3tl::checked_multiply<sal_Int64>(n, 72, n) || o3tl::checked_sub<sal_Int64>(n, 63, n))
             n = SAL_MIN_INT64;
     }
-    return n / 127;
+    return n / 127; // 127 is 2,540 100th-mm divided by 20pts
 }
 
 #endif
diff --git a/tools/CppunitTest_tools_test.mk b/tools/CppunitTest_tools_test.mk
index 2c24b21878fa..7c7b9eab6184 100644
--- a/tools/CppunitTest_tools_test.mk
+++ b/tools/CppunitTest_tools_test.mk
@@ -25,6 +25,7 @@ $(eval $(call gb_CppunitTest_add_exception_objects,tools_test, \
     tools/qa/cppunit/test_color \
     tools/qa/cppunit/test_rectangle \
     tools/qa/cppunit/test_minmax \
+    tools/qa/cppunit/test_100mm2twips \
 ))
 
 $(eval $(call gb_CppunitTest_use_sdk_api,tools_test))
diff --git a/tools/qa/cppunit/test_100mm2twips.cxx b/tools/qa/cppunit/test_100mm2twips.cxx
new file mode 100644
index 000000000000..93eab264f8da
--- /dev/null
+++ b/tools/qa/cppunit/test_100mm2twips.cxx
@@ -0,0 +1,55 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/*
+ * This file is part of the LibreOffice project.
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ *
+ * This file incorporates work covered by the following license notice:
+ *
+ *   Licensed to the Apache Software Foundation (ASF) under one or more
+ *   contributor license agreements. See the NOTICE file distributed
+ *   with this work for additional information regarding copyright
+ *   ownership. The ASF licenses this file to you under the Apache
+ *   License, Version 2.0 (the "License"); you may not use this file
+ *   except in compliance with the License. You may obtain a copy of
+ *   the License at http://www.apache.org/licenses/LICENSE-2.0 .
+ */
+
+#include <sal/types.h>
+#include <sal/log.hxx>
+
+#include <cppunit/TestFixture.h>
+#include <cppunit/extensions/HelperMacros.h>
+#include <cppunit/plugin/TestPlugIn.h>
+
+#include <tools/helpers.hxx>
+
+#include <cassert>
+
+namespace tools
+{
+class cm2TwipsTest : public CppUnit::TestFixture
+{
+public:
+    void testConvert()
+    {
+        sal_Int32 nActual = sanitiseMm100ToTwip(255);
+        sal_Int32 nExpected = 145;
+        CPPUNIT_ASSERT_EQUAL(nExpected, nActual);
+
+        nActual = sanitiseMm100ToTwip(-255);
+        nExpected = -145;
+        CPPUNIT_ASSERT_EQUAL(nExpected, nActual);
+    }
+
+    CPPUNIT_TEST_SUITE(cm2TwipsTest);
+    CPPUNIT_TEST(testConvert);
+    CPPUNIT_TEST_SUITE_END();
+};
+
+CPPUNIT_TEST_SUITE_REGISTRATION(cm2TwipsTest);
+} // namespace tools
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab: */
-- 
cgit