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[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

llvm-svn: 347324
This commit is contained in:
Sanjay Patel 2018-11-20 16:47:59 +00:00
parent 8ce71fb2c7
commit 7ef0b31389
3 changed files with 66 additions and 0 deletions
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6
llvm/include/llvm/ADT/APInt.h
View File

@ -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

36
llvm/lib/Support/APInt.cpp
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@ -1947,7 +1947,43 @@ APInt APInt::ushl_ov(const APInt &ShAmt, bool &Overflow) const {
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) {

24
llvm/unittests/ADT/APIntTest.cpp
View File

@ -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)));
}