Unverified Commit 4ae338ff authored by Luca Ciucci's avatar Luca Ciucci Committed by GitHub
Browse files

APFloat: fix wrong result status for large floats (#189925) 

For large float literals such as
`10384593717069655257060992658440193.0`,
[`FloatingLiteral::isExact`](https://github.com/llvm/llvm-project/blob/6b2b0da40de1495ace2b100799a35711f7ad7b21/clang/include/clang/AST/Expr.h#L1702)
was incorrectly returning `true`.

The issue has been tracked down to
`IEEEFloat::roundSignificandWithExponent` incorrectly reporting `opOK`.
parent 4f40fe10

llvm/lib/Support/APFloat.cpp

+6 −6
Original line number Diff line number Diff line
@@ -2856,7 +2856,6 @@ IEEEFloat::roundSignificandWithExponent(const integerPart *decSigParts, 
  unsigned pow5PartCount = powerOf5(pow5Parts, exp >= 0 ? exp : -exp);



  for (;; parts *= 2) {

    opStatus sigStatus, powStatus;

    unsigned int excessPrecision, truncatedBits;



    calcSemantics.precision = parts * integerPartWidth - 1;
@@ -2867,9 +2866,9 @@ IEEEFloat::roundSignificandWithExponent(const integerPart *decSigParts, 
    decSig.makeZero(sign);

    IEEEFloat pow5(calcSemantics);



    sigStatus = decSig.convertFromUnsignedParts(decSigParts, sigPartCount,

                                                rmNearestTiesToEven);

    powStatus = pow5.convertFromUnsignedParts(pow5Parts, pow5PartCount,

    opStatus sigStatus = decSig.convertFromUnsignedParts(

        decSigParts, sigPartCount, rmNearestTiesToEven);

    opStatus powStatus = pow5.convertFromUnsignedParts(pow5Parts, pow5PartCount,

                                                       rmNearestTiesToEven);

    /* Add exp, as 10^n = 5^n * 2^n.  */

    decSig.exponent += exp;
@@ -2917,7 +2916,8 @@ IEEEFloat::roundSignificandWithExponent(const integerPart *decSigParts, 
      calcLostFraction = lostFractionThroughTruncation(decSig.significandParts(),

                                                       decSig.partCount(),

                                                       truncatedBits);

      return normalize(rounding_mode, calcLostFraction);

      return static_cast<opStatus>(normalize(rounding_mode, calcLostFraction) |

                                   ((sigStatus | powStatus) & opInexact));

    }

  }

}

llvm/unittests/ADT/APFloatTest.cpp

+22 −0
Original line number Diff line number Diff line
@@ -10206,4 +10206,26 @@ TEST(APFloatTest, isValidArbitraryFPFormat) { 
  EXPECT_FALSE(APFloat::isValidArbitraryFPFormat("unknown"));

}



TEST(APFloatTest, DecimalStringPreservesInexactStatus) {

  APFloat F(APFloat::IEEEsingle());



  auto StatusOr = F.convertFromString("10384593717069655257060992658440193.0",

                                      APFloat::rmNearestTiesToEven);

  EXPECT_TRUE(!!StatusOr);



  APFloat::opStatus Status = *StatusOr;



  // The value is 2^113 + 1, not exactly representable in float.

  EXPECT_TRUE(Status & APFloat::opInexact);



  // But it should round to exactly 2^113.

  APFloat Expected(APFloat::IEEEsingle());

  auto ExpectedStatus =

      Expected.convertFromString("0x1p113", APFloat::rmNearestTiesToEven);

  EXPECT_TRUE(!!ExpectedStatus);

  EXPECT_FALSE(*ExpectedStatus & APFloat::opInexact);



  EXPECT_EQ(F.bitcastToAPInt(), Expected.bitcastToAPInt());

}



} // namespace