From 68a5ef1a63fdf9f2b15bd3dc98a40b19eb05d56a Mon Sep 17 00:00:00 2001
From: "Duncan P. N. Exon Smith" <dexonsmith@apple.com>
Date: Mon, 23 Jun 2014 23:14:51 +0000
Subject: [PATCH] Support: Return scale from ScaledNumbers::matchScales()

This will be convenient when extracting `ScaledNumbers::getSum()`.

llvm-svn: 211552
---
 llvm/include/llvm/Support/ScaledNumber.h    | 29 ++++++++++++---------
 llvm/unittests/Support/ScaledNumberTest.cpp |  2 +-
 2 files changed, 17 insertions(+), 14 deletions(-)

diff --git a/llvm/include/llvm/Support/ScaledNumber.h b/llvm/include/llvm/Support/ScaledNumber.h
index b1f6eadab842..caca5f731d48 100644
--- a/llvm/include/llvm/Support/ScaledNumber.h
+++ b/llvm/include/llvm/Support/ScaledNumber.h
@@ -271,28 +271,30 @@ int compare(DigitsT LDigits, int16_t LScale, DigitsT RDigits, int16_t RScale) {
 /// losing precision only when necessary.
 ///
 /// If the output value of \c LDigits (\c RDigits) is \c 0, the output value of
-/// \c LScale (\c RScale) is unspecified.  If both \c LDigits and \c RDigits
-/// are \c 0, the output value is one of \c LScale and \c RScale; which is
-/// unspecified.
+/// \c LScale (\c RScale) is unspecified.
+///
+/// As a convenience, returns the matching scale.  If the output value of one
+/// number is zero, returns the scale of the other.  If both are zero, which
+/// scale is returned is unspecifed.
 template <class DigitsT>
-void matchScales(DigitsT &LDigits, int16_t &LScale, DigitsT &RDigits,
-                 int16_t &RScale) {
+int16_t matchScales(DigitsT &LDigits, int16_t &LScale, DigitsT &RDigits,
+                    int16_t &RScale) {
   static_assert(!std::numeric_limits<DigitsT>::is_signed, "expected unsigned");
 
-  if (LScale < RScale) {
+  if (LScale < RScale)
     // Swap arguments.
-    matchScales(RDigits, RScale, LDigits, LScale);
-    return;
-  }
-  if (!LDigits || !RDigits || LScale == RScale)
-    return;
+    return matchScales(RDigits, RScale, LDigits, LScale);
+  if (!LDigits)
+    return RScale;
+  if (!RDigits || LScale == RScale)
+    return LScale;
 
   // Now LScale > RScale.  Get the difference.
   int32_t ScaleDiff = int32_t(LScale) - RScale;
   if (ScaleDiff >= 2 * getWidth<DigitsT>()) {
     // Don't bother shifting.  RDigits will get zero-ed out anyway.
     RDigits = 0;
-    return;
+    return LScale;
   }
 
   // Shift LDigits left as much as possible, then shift RDigits right.
@@ -303,7 +305,7 @@ void matchScales(DigitsT &LDigits, int16_t &LScale, DigitsT &RDigits,
   if (ShiftR >= getWidth<DigitsT>()) {
     // Don't bother shifting.  RDigits will get zero-ed out anyway.
     RDigits = 0;
-    return;
+    return LScale;
   }
 
   LDigits <<= ShiftL;
@@ -312,6 +314,7 @@ void matchScales(DigitsT &LDigits, int16_t &LScale, DigitsT &RDigits,
   LScale -= ShiftL;
   RScale += ShiftR;
   assert(LScale == RScale && "scales should match");
+  return LScale;
 }
 
 } // end namespace ScaledNumbers
diff --git a/llvm/unittests/Support/ScaledNumberTest.cpp b/llvm/unittests/Support/ScaledNumberTest.cpp
index 550947b8ea3f..08d6c68b0e06 100644
--- a/llvm/unittests/Support/ScaledNumberTest.cpp
+++ b/llvm/unittests/Support/ScaledNumberTest.cpp
@@ -336,7 +336,7 @@ TEST(ScaledNumberHelpersTest, matchScales) {
     int16_t RSx = RSIn;                                                        \
     int16_t Sy = SOut;                                                         \
                                                                                \
-    matchScales(LDx, LSx, RDx, RSx);                                           \
+    EXPECT_EQ(SOut, matchScales(LDx, LSx, RDx, RSx));                          \
     EXPECT_EQ(LDy, LDx);                                                       \
     EXPECT_EQ(RDy, RDx);                                                       \
     if (LDy)                                                                   \