[PATCH] D69397: [APInt} Add saturating multiply ops

[Roman Lebedev via Phabricator via llvm-commits]

lebedev.ri created this revision.
lebedev.ri added reviewers: spatel, nikic.
lebedev.ri added a project: LLVM.
Herald added subscribers: dexonsmith, hiraditya.
lebedev.ri added a child revision: D69398: [APInt} Add saturating left-shift ops.

There are `*_ov()` functions already, so at least for consistency it may be good to also have saturating variants.
These may or may not be needed for `ConstantRange`'s `mulWithNoWrap()`


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D69397

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


Index: llvm/unittests/ADT/APIntTest.cpp
===================================================================
--- llvm/unittests/ADT/APIntTest.cpp
+++ llvm/unittests/ADT/APIntTest.cpp
@@ -1197,6 +1197,24 @@
   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)));
+
+  EXPECT_EQ(APInt(8, 250), APInt(8, 50).umul_sat(APInt(8, 5)));
+  EXPECT_EQ(APInt(8, 255), APInt(8, 50).umul_sat(APInt(8, 6)));
+  EXPECT_EQ(APInt(8, 255), APInt(8, -128).umul_sat(APInt(8, 3)));
+  EXPECT_EQ(APInt(8, 255), APInt(8, 3).umul_sat(APInt(8, -128)));
+  EXPECT_EQ(APInt(8, 255), APInt(8, -128).umul_sat(APInt(8, -128)));
+
+  EXPECT_EQ(APInt(8, 125), APInt(8, 25).smul_sat(APInt(8, 5)));
+  EXPECT_EQ(APInt(8, 127), APInt(8, 25).smul_sat(APInt(8, 6)));
+  EXPECT_EQ(APInt(8, 127), APInt(8, 127).smul_sat(APInt(8, 127)));
+  EXPECT_EQ(APInt(8, -125), APInt(8, -25).smul_sat(APInt(8, 5)));
+  EXPECT_EQ(APInt(8, -125), APInt(8, 25).smul_sat(APInt(8, -5)));
+  EXPECT_EQ(APInt(8, 125), APInt(8, -25).smul_sat(APInt(8, -5)));
+  EXPECT_EQ(APInt(8, 125), APInt(8, 25).smul_sat(APInt(8, 5)));
+  EXPECT_EQ(APInt(8, -128), APInt(8, -25).smul_sat(APInt(8, 6)));
+  EXPECT_EQ(APInt(8, -128), APInt(8, 25).smul_sat(APInt(8, -6)));
+  EXPECT_EQ(APInt(8, 127), APInt(8, -25).smul_sat(APInt(8, -6)));
+  EXPECT_EQ(APInt(8, 127), APInt(8, 25).smul_sat(APInt(8, 6)));
 }
 
 TEST(APIntTest, FromArray) {
Index: llvm/lib/Support/APInt.cpp
===================================================================
--- llvm/lib/Support/APInt.cpp
+++ llvm/lib/Support/APInt.cpp
@@ -2048,6 +2048,27 @@
   return APInt(BitWidth, 0);
 }
 
+APInt APInt::smul_sat(const APInt &RHS) const {
+  bool Overflow;
+  APInt Res = smul_ov(RHS, Overflow);
+  if (!Overflow)
+    return Res;
+
+  // The result is negative if one and only one of inputs is negative.
+  bool ResIsNegative = isNegative() ^ RHS.isNegative();
+
+  return ResIsNegative ? APInt::getSignedMinValue(BitWidth)
+                       : APInt::getSignedMaxValue(BitWidth);
+}
+
+APInt APInt::umul_sat(const APInt &RHS) const {
+  bool Overflow;
+  APInt Res = umul_ov(RHS, Overflow);
+  if (!Overflow)
+    return Res;
+
+  return APInt::getMaxValue(BitWidth);
+}
 
 void APInt::fromString(unsigned numbits, StringRef str, uint8_t radix) {
   // Check our assumptions here
Index: llvm/include/llvm/ADT/APInt.h
===================================================================
--- llvm/include/llvm/ADT/APInt.h
+++ llvm/include/llvm/ADT/APInt.h
@@ -1109,6 +1109,8 @@
   APInt uadd_sat(const APInt &RHS) const;
   APInt ssub_sat(const APInt &RHS) const;
   APInt usub_sat(const APInt &RHS) const;
+  APInt smul_sat(const APInt &RHS) const;
+  APInt umul_sat(const APInt &RHS) const;
 
   /// Array-indexing support.
   ///


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