[PATCH] D54332: [APInt] Add methods for saturated add and sub

[Nikita Popov via Phabricator via llvm-commits]

nikic created this revision.
nikic added a reviewer: RKSimon.
Herald added subscribers: llvm-commits, kristina, dexonsmith.

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

Split out from https://reviews.llvm.org/D54237.


Repository:
  rL LLVM

https://reviews.llvm.org/D54332

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


Index: unittests/ADT/APIntTest.cpp
===================================================================
--- unittests/ADT/APIntTest.cpp
+++ unittests/ADT/APIntTest.cpp
@@ -1176,6 +1176,30 @@
   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)));
 }
Index: lib/Support/APInt.cpp
===================================================================
--- lib/Support/APInt.cpp
+++ lib/Support/APInt.cpp
@@ -1947,7 +1947,43 @@
   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) {
Index: include/llvm/ADT/APInt.h
===================================================================
--- include/llvm/ADT/APInt.h
+++ include/llvm/ADT/APInt.h
@@ -1105,6 +1105,12 @@
   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


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