From 69c9c8c4cf57d49a0c64507082617f433372831d Mon Sep 17 00:00:00 2001 From: Ulrich Weigand Date: Mon, 29 Oct 2012 18:09:01 +0000 Subject: [PATCH] Implement arithmetic on APFloat with PPCDoubleDouble semantics by treating it as if it were an IEEE floating-point type with 106-bit mantissa. This makes compile-time arithmetic on "long double" for PowerPC in clang (in particular parsing of floating point constants) work, and fixes all "long double" related failures in the test suite. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@166951 91177308-0d34-0410-b5e6-96231b3b80d8 --- lib/Support/APFloat.cpp | 139 ++++++++++++++++------------------ unittests/ADT/APFloatTest.cpp | 36 +++++++++ 2 files changed, 100 insertions(+), 75 deletions(-) diff --git a/lib/Support/APFloat.cpp b/lib/Support/APFloat.cpp index d07a3c9e7f3..033512fb498 100644 --- a/lib/Support/APFloat.cpp +++ b/lib/Support/APFloat.cpp @@ -58,10 +58,19 @@ namespace llvm { const fltSemantics APFloat::x87DoubleExtended = { 16383, -16382, 64, true }; const fltSemantics APFloat::Bogus = { 0, 0, 0, true }; - // The PowerPC format consists of two doubles. It does not map cleanly - // onto the usual format above. For now only storage of constants of - // this type is supported, no arithmetic. - const fltSemantics APFloat::PPCDoubleDouble = { 1023, -1022, 106, false }; + /* The PowerPC format consists of two doubles. It does not map cleanly + onto the usual format above. It is approximated using twice the + mantissa bits. Note that for exponents near the double minimum, + we no longer can represent the full 106 mantissa bits, so those + will be treated as denormal numbers. + + FIXME: While this approximation is equivalent to what GCC uses for + compile-time arithmetic on PPC double-double numbers, it is not able + to represent all possible values held by a PPC double-double number, + for example: (long double) 1.0 + (long double) 0x1p-106 + Should this be replaced by a full emulation of PPC double-double? */ + const fltSemantics APFloat::PPCDoubleDouble = + { 1023, -1022 + 53, 53 + 53, true }; /* A tight upper bound on number of parts required to hold the value pow(5, power) is @@ -2790,42 +2799,46 @@ APFloat::convertPPCDoubleDoubleAPFloatToAPInt() const assert(semantics == (const llvm::fltSemantics*)&PPCDoubleDouble); assert(partCount()==2); - uint64_t myexponent, mysignificand, myexponent2, mysignificand2; + uint64_t words[2]; + opStatus fs; + bool losesInfo; - if (category==fcNormal) { - myexponent = exponent + 1023; //bias - myexponent2 = exponent2 + 1023; - mysignificand = significandParts()[0]; - mysignificand2 = significandParts()[1]; - if (myexponent==1 && !(mysignificand & 0x10000000000000LL)) - myexponent = 0; // denormal - if (myexponent2==1 && !(mysignificand2 & 0x10000000000000LL)) - myexponent2 = 0; // denormal - } else if (category==fcZero) { - myexponent = 0; - mysignificand = 0; - myexponent2 = 0; - mysignificand2 = 0; - } else if (category==fcInfinity) { - myexponent = 0x7ff; - myexponent2 = 0; - mysignificand = 0; - mysignificand2 = 0; + // Convert number to double. To avoid spurious underflows, we re- + // normalize against the "double" minExponent first, and only *then* + // truncate the mantissa. The result of that second conversion + // may be inexact, but should never underflow. + APFloat extended(*this); + fltSemantics extendedSemantics = *semantics; + extendedSemantics.minExponent = IEEEdouble.minExponent; + fs = extended.convert(extendedSemantics, rmNearestTiesToEven, &losesInfo); + assert(fs == opOK && !losesInfo); + (void)fs; + + APFloat u(extended); + fs = u.convert(IEEEdouble, rmNearestTiesToEven, &losesInfo); + assert(fs == opOK || fs == opInexact); + (void)fs; + words[0] = *u.convertDoubleAPFloatToAPInt().getRawData(); + + // If conversion was exact or resulted in a special case, we're done; + // just set the second double to zero. Otherwise, re-convert back to + // the extended format and compute the difference. This now should + // convert exactly to double. + if (u.category == fcNormal && losesInfo) { + fs = u.convert(extendedSemantics, rmNearestTiesToEven, &losesInfo); + assert(fs == opOK && !losesInfo); + (void)fs; + + APFloat v(extended); + v.subtract(u, rmNearestTiesToEven); + fs = v.convert(IEEEdouble, rmNearestTiesToEven, &losesInfo); + assert(fs == opOK && !losesInfo); + (void)fs; + words[1] = *v.convertDoubleAPFloatToAPInt().getRawData(); } else { - assert(category == fcNaN && "Unknown category"); - myexponent = 0x7ff; - mysignificand = significandParts()[0]; - myexponent2 = exponent2; - mysignificand2 = significandParts()[1]; + words[1] = 0; } - uint64_t words[2]; - words[0] = ((uint64_t)(sign & 1) << 63) | - ((myexponent & 0x7ff) << 52) | - (mysignificand & 0xfffffffffffffLL); - words[1] = ((uint64_t)(sign2 & 1) << 63) | - ((myexponent2 & 0x7ff) << 52) | - (mysignificand2 & 0xfffffffffffffLL); return APInt(128, words); } @@ -3045,47 +3058,23 @@ APFloat::initFromPPCDoubleDoubleAPInt(const APInt &api) assert(api.getBitWidth()==128); uint64_t i1 = api.getRawData()[0]; uint64_t i2 = api.getRawData()[1]; - uint64_t myexponent = (i1 >> 52) & 0x7ff; - uint64_t mysignificand = i1 & 0xfffffffffffffLL; - uint64_t myexponent2 = (i2 >> 52) & 0x7ff; - uint64_t mysignificand2 = i2 & 0xfffffffffffffLL; + opStatus fs; + bool losesInfo; - initialize(&APFloat::PPCDoubleDouble); - assert(partCount()==2); + // Get the first double and convert to our format. + initFromDoubleAPInt(APInt(64, i1)); + fs = convert(PPCDoubleDouble, rmNearestTiesToEven, &losesInfo); + assert(fs == opOK && !losesInfo); + (void)fs; - sign = static_cast(i1>>63); - sign2 = static_cast(i2>>63); - if (myexponent==0 && mysignificand==0) { - // exponent, significand meaningless - // exponent2 and significand2 are required to be 0; we don't check - category = fcZero; - } else if (myexponent==0x7ff && mysignificand==0) { - // exponent, significand meaningless - // exponent2 and significand2 are required to be 0; we don't check - category = fcInfinity; - } else if (myexponent==0x7ff && mysignificand!=0) { - // exponent meaningless. So is the whole second word, but keep it - // for determinism. - category = fcNaN; - exponent2 = myexponent2; - significandParts()[0] = mysignificand; - significandParts()[1] = mysignificand2; - } else { - category = fcNormal; - // Note there is no category2; the second word is treated as if it is - // fcNormal, although it might be something else considered by itself. - exponent = myexponent - 1023; - exponent2 = myexponent2 - 1023; - significandParts()[0] = mysignificand; - significandParts()[1] = mysignificand2; - if (myexponent==0) // denormal - exponent = -1022; - else - significandParts()[0] |= 0x10000000000000LL; // integer bit - if (myexponent2==0) - exponent2 = -1022; - else - significandParts()[1] |= 0x10000000000000LL; // integer bit + // Unless we have a special case, add in second double. + if (category == fcNormal) { + APFloat v(APInt(64, i2)); + fs = v.convert(PPCDoubleDouble, rmNearestTiesToEven, &losesInfo); + assert(fs == opOK && !losesInfo); + (void)fs; + + add(v, rmNearestTiesToEven); } } diff --git a/unittests/ADT/APFloatTest.cpp b/unittests/ADT/APFloatTest.cpp index c8d7177d866..48d5d830193 100644 --- a/unittests/ADT/APFloatTest.cpp +++ b/unittests/ADT/APFloatTest.cpp @@ -737,4 +737,40 @@ TEST(APFloatTest, convert) { EXPECT_EQ(4294967295.0, test.convertToDouble()); EXPECT_FALSE(losesInfo); } + +TEST(APFloatTest, PPCDoubleDouble) { + APFloat test(APFloat::PPCDoubleDouble, "1.0"); + EXPECT_EQ(0x3ff0000000000000ull, test.bitcastToAPInt().getRawData()[0]); + EXPECT_EQ(0x0000000000000000ull, test.bitcastToAPInt().getRawData()[1]); + + test.divide(APFloat(APFloat::PPCDoubleDouble, "3.0"), APFloat::rmNearestTiesToEven); + EXPECT_EQ(0x3fd5555555555555ull, test.bitcastToAPInt().getRawData()[0]); + EXPECT_EQ(0x3c75555555555556ull, test.bitcastToAPInt().getRawData()[1]); + + // LDBL_MAX + test = APFloat(APFloat::PPCDoubleDouble, "1.79769313486231580793728971405301e+308"); + EXPECT_EQ(0x7fefffffffffffffull, test.bitcastToAPInt().getRawData()[0]); + EXPECT_EQ(0x7c8ffffffffffffeull, test.bitcastToAPInt().getRawData()[1]); + + // LDBL_MIN + test = APFloat(APFloat::PPCDoubleDouble, "2.00416836000897277799610805135016e-292"); + EXPECT_EQ(0x0360000000000000ull, test.bitcastToAPInt().getRawData()[0]); + EXPECT_EQ(0x0000000000000000ull, test.bitcastToAPInt().getRawData()[1]); + + test = APFloat(APFloat::PPCDoubleDouble, "1.0"); + test.add(APFloat(APFloat::PPCDoubleDouble, "0x1p-105"), APFloat::rmNearestTiesToEven); + EXPECT_EQ(0x3ff0000000000000ull, test.bitcastToAPInt().getRawData()[0]); + EXPECT_EQ(0x3960000000000000ull, test.bitcastToAPInt().getRawData()[1]); + + test = APFloat(APFloat::PPCDoubleDouble, "1.0"); + test.add(APFloat(APFloat::PPCDoubleDouble, "0x1p-106"), APFloat::rmNearestTiesToEven); + EXPECT_EQ(0x3ff0000000000000ull, test.bitcastToAPInt().getRawData()[0]); +#if 0 // XFAIL + // This is what we would expect with a true double-double implementation + EXPECT_EQ(0x3950000000000000ull, test.bitcastToAPInt().getRawData()[1]); +#else + // This is what we get with our 106-bit mantissa approximation + EXPECT_EQ(0x0000000000000000ull, test.bitcastToAPInt().getRawData()[1]); +#endif +} }