[llvm] r347324 - [APInt] Add methods for saturated add and sub

[Sanjay Patel via llvm-commits]

Author: spatel
Date: Tue Nov 20 08:47:59 2018
New Revision: 347324

URL: http://llvm.org/viewvc/llvm-project?rev=347324&view=rev
Log:
[APInt] Add methods for saturated add and sub

This adds the sadd_sat, uadd_sat, ssub_sat, usub_sat methods for performing saturating additions and subtractions to APInt.

Split out from D54237.

Patch by: nikic (Nikita Popov)

Differential Revision: https://reviews.llvm.org/D54332

Modified:
    llvm/trunk/include/llvm/ADT/APInt.h
    llvm/trunk/lib/Support/APInt.cpp
    llvm/trunk/unittests/ADT/APIntTest.cpp

Modified: llvm/trunk/include/llvm/ADT/APInt.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/ADT/APInt.h?rev=347324&r1=347323&r2=347324&view=diff
==============================================================================
--- llvm/trunk/include/llvm/ADT/APInt.h (original)
+++ llvm/trunk/include/llvm/ADT/APInt.h Tue Nov 20 08:47:59 2018
@@ -1105,6 +1105,12 @@ public:
   APInt sshl_ov(const APInt &Amt, bool &Overflow) const;
   APInt ushl_ov(const APInt &Amt, bool &Overflow) const;
 
+  // Operations that saturate
+  APInt sadd_sat(const APInt &RHS) const;
+  APInt uadd_sat(const APInt &RHS) const;
+  APInt ssub_sat(const APInt &RHS) const;
+  APInt usub_sat(const APInt &RHS) const;
+
   /// Array-indexing support.
   ///
   /// \returns the bit value at bitPosition

Modified: llvm/trunk/lib/Support/APInt.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Support/APInt.cpp?rev=347324&r1=347323&r2=347324&view=diff
==============================================================================
--- llvm/trunk/lib/Support/APInt.cpp (original)
+++ llvm/trunk/lib/Support/APInt.cpp Tue Nov 20 08:47:59 2018
@@ -1947,7 +1947,43 @@ APInt APInt::ushl_ov(const APInt &ShAmt,
   return *this << ShAmt;
 }
 
+APInt APInt::sadd_sat(const APInt &RHS) const {
+  bool Overflow;
+  APInt Res = sadd_ov(RHS, Overflow);
+  if (!Overflow)
+    return Res;
 
+  return isNegative() ? APInt::getSignedMinValue(BitWidth)
+                      : APInt::getSignedMaxValue(BitWidth);
+}
+
+APInt APInt::uadd_sat(const APInt &RHS) const {
+  bool Overflow;
+  APInt Res = uadd_ov(RHS, Overflow);
+  if (!Overflow)
+    return Res;
+
+  return APInt::getMaxValue(BitWidth);
+}
+
+APInt APInt::ssub_sat(const APInt &RHS) const {
+  bool Overflow;
+  APInt Res = ssub_ov(RHS, Overflow);
+  if (!Overflow)
+    return Res;
+
+  return isNegative() ? APInt::getSignedMinValue(BitWidth)
+                      : APInt::getSignedMaxValue(BitWidth);
+}
+
+APInt APInt::usub_sat(const APInt &RHS) const {
+  bool Overflow;
+  APInt Res = usub_ov(RHS, Overflow);
+  if (!Overflow)
+    return Res;
+
+  return APInt(BitWidth, 0);
+}
 
 
 void APInt::fromString(unsigned numbits, StringRef str, uint8_t radix) {

Modified: llvm/trunk/unittests/ADT/APIntTest.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/unittests/ADT/APIntTest.cpp?rev=347324&r1=347323&r2=347324&view=diff
==============================================================================
--- llvm/trunk/unittests/ADT/APIntTest.cpp (original)
+++ llvm/trunk/unittests/ADT/APIntTest.cpp Tue Nov 20 08:47:59 2018
@@ -1176,6 +1176,30 @@ TEST(APIntTest, fromString) {
   EXPECT_EQ(APInt(32, uint64_t(-72LL)), APInt(32, "-20", 36));
 }
 
+TEST(APIntTest, SaturatingMath) {
+  APInt AP_10 = APInt(8, 10);
+  APInt AP_100 = APInt(8, 100);
+  APInt AP_200 = APInt(8, 200);
+
+  EXPECT_EQ(APInt(8, 200), AP_100.uadd_sat(AP_100));
+  EXPECT_EQ(APInt(8, 255), AP_100.uadd_sat(AP_200));
+  EXPECT_EQ(APInt(8, 255), APInt(8, 255).uadd_sat(APInt(8, 255)));
+
+  EXPECT_EQ(APInt(8, 110), AP_10.sadd_sat(AP_100));
+  EXPECT_EQ(APInt(8, 127), AP_100.sadd_sat(AP_100));
+  EXPECT_EQ(APInt(8, -128), (-AP_100).sadd_sat(-AP_100));
+  EXPECT_EQ(APInt(8, -128), APInt(8, -128).sadd_sat(APInt(8, -128)));
+
+  EXPECT_EQ(APInt(8, 90), AP_100.usub_sat(AP_10));
+  EXPECT_EQ(APInt(8, 0), AP_100.usub_sat(AP_200));
+  EXPECT_EQ(APInt(8, 0), APInt(8, 0).usub_sat(APInt(8, 255)));
+
+  EXPECT_EQ(APInt(8, -90), AP_10.ssub_sat(AP_100));
+  EXPECT_EQ(APInt(8, 127), AP_100.ssub_sat(-AP_100));
+  EXPECT_EQ(APInt(8, -128), (-AP_100).ssub_sat(AP_100));
+  EXPECT_EQ(APInt(8, -128), APInt(8, -128).ssub_sat(APInt(8, 127)));
+}
+
 TEST(APIntTest, FromArray) {
   EXPECT_EQ(APInt(32, uint64_t(1)), APInt(32, ArrayRef<uint64_t>(1)));
 }