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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
This commit is contained in:
Ulrich Weigand
parent
2fbc239e4f
commit
69c9c8c4cf
@ -58,10 +58,19 @@ namespace llvm {
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const fltSemantics APFloat::x87DoubleExtended = { 16383, -16382, 64, true };
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const fltSemantics APFloat::Bogus = { 0, 0, 0, true };
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// The PowerPC format consists of two doubles. It does not map cleanly
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// onto the usual format above. For now only storage of constants of
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// this type is supported, no arithmetic.
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const fltSemantics APFloat::PPCDoubleDouble = { 1023, -1022, 106, false };
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/* The PowerPC format consists of two doubles. It does not map cleanly
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onto the usual format above. It is approximated using twice the
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mantissa bits. Note that for exponents near the double minimum,
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we no longer can represent the full 106 mantissa bits, so those
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will be treated as denormal numbers.
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FIXME: While this approximation is equivalent to what GCC uses for
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compile-time arithmetic on PPC double-double numbers, it is not able
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to represent all possible values held by a PPC double-double number,
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for example: (long double) 1.0 + (long double) 0x1p-106
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Should this be replaced by a full emulation of PPC double-double? */
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const fltSemantics APFloat::PPCDoubleDouble =
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{ 1023, -1022 + 53, 53 + 53, true };
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/* A tight upper bound on number of parts required to hold the value
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pow(5, power) is
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@ -2790,42 +2799,46 @@ APFloat::convertPPCDoubleDoubleAPFloatToAPInt() const
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assert(semantics == (const llvm::fltSemantics*)&PPCDoubleDouble);
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assert(partCount()==2);
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uint64_t myexponent, mysignificand, myexponent2, mysignificand2;
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uint64_t words[2];
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opStatus fs;
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bool losesInfo;
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if (category==fcNormal) {
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myexponent = exponent + 1023; //bias
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myexponent2 = exponent2 + 1023;
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mysignificand = significandParts()[0];
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mysignificand2 = significandParts()[1];
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if (myexponent==1 && !(mysignificand & 0x10000000000000LL))
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myexponent = 0; // denormal
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if (myexponent2==1 && !(mysignificand2 & 0x10000000000000LL))
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myexponent2 = 0; // denormal
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} else if (category==fcZero) {
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myexponent = 0;
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mysignificand = 0;
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myexponent2 = 0;
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mysignificand2 = 0;
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} else if (category==fcInfinity) {
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myexponent = 0x7ff;
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myexponent2 = 0;
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mysignificand = 0;
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mysignificand2 = 0;
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// Convert number to double. To avoid spurious underflows, we re-
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// normalize against the "double" minExponent first, and only *then*
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// truncate the mantissa. The result of that second conversion
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// may be inexact, but should never underflow.
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APFloat extended(*this);
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fltSemantics extendedSemantics = *semantics;
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extendedSemantics.minExponent = IEEEdouble.minExponent;
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fs = extended.convert(extendedSemantics, rmNearestTiesToEven, &losesInfo);
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assert(fs == opOK && !losesInfo);
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(void)fs;
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APFloat u(extended);
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fs = u.convert(IEEEdouble, rmNearestTiesToEven, &losesInfo);
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assert(fs == opOK || fs == opInexact);
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(void)fs;
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words[0] = *u.convertDoubleAPFloatToAPInt().getRawData();
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// If conversion was exact or resulted in a special case, we're done;
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// just set the second double to zero. Otherwise, re-convert back to
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// the extended format and compute the difference. This now should
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// convert exactly to double.
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if (u.category == fcNormal && losesInfo) {
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fs = u.convert(extendedSemantics, rmNearestTiesToEven, &losesInfo);
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assert(fs == opOK && !losesInfo);
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(void)fs;
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APFloat v(extended);
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v.subtract(u, rmNearestTiesToEven);
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fs = v.convert(IEEEdouble, rmNearestTiesToEven, &losesInfo);
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assert(fs == opOK && !losesInfo);
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(void)fs;
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words[1] = *v.convertDoubleAPFloatToAPInt().getRawData();
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} else {
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assert(category == fcNaN && "Unknown category");
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myexponent = 0x7ff;
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mysignificand = significandParts()[0];
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myexponent2 = exponent2;
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mysignificand2 = significandParts()[1];
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words[1] = 0;
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}
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uint64_t words[2];
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words[0] = ((uint64_t)(sign & 1) << 63) |
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((myexponent & 0x7ff) << 52) |
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(mysignificand & 0xfffffffffffffLL);
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words[1] = ((uint64_t)(sign2 & 1) << 63) |
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((myexponent2 & 0x7ff) << 52) |
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(mysignificand2 & 0xfffffffffffffLL);
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return APInt(128, words);
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}
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@ -3045,47 +3058,23 @@ APFloat::initFromPPCDoubleDoubleAPInt(const APInt &api)
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assert(api.getBitWidth()==128);
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uint64_t i1 = api.getRawData()[0];
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uint64_t i2 = api.getRawData()[1];
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uint64_t myexponent = (i1 >> 52) & 0x7ff;
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uint64_t mysignificand = i1 & 0xfffffffffffffLL;
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uint64_t myexponent2 = (i2 >> 52) & 0x7ff;
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uint64_t mysignificand2 = i2 & 0xfffffffffffffLL;
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opStatus fs;
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bool losesInfo;
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initialize(&APFloat::PPCDoubleDouble);
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assert(partCount()==2);
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// Get the first double and convert to our format.
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initFromDoubleAPInt(APInt(64, i1));
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fs = convert(PPCDoubleDouble, rmNearestTiesToEven, &losesInfo);
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assert(fs == opOK && !losesInfo);
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(void)fs;
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sign = static_cast<unsigned int>(i1>>63);
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sign2 = static_cast<unsigned int>(i2>>63);
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if (myexponent==0 && mysignificand==0) {
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// exponent, significand meaningless
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// exponent2 and significand2 are required to be 0; we don't check
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category = fcZero;
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} else if (myexponent==0x7ff && mysignificand==0) {
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// exponent, significand meaningless
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// exponent2 and significand2 are required to be 0; we don't check
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category = fcInfinity;
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} else if (myexponent==0x7ff && mysignificand!=0) {
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// exponent meaningless. So is the whole second word, but keep it
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// for determinism.
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category = fcNaN;
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exponent2 = myexponent2;
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significandParts()[0] = mysignificand;
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significandParts()[1] = mysignificand2;
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} else {
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category = fcNormal;
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// Note there is no category2; the second word is treated as if it is
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// fcNormal, although it might be something else considered by itself.
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exponent = myexponent - 1023;
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exponent2 = myexponent2 - 1023;
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significandParts()[0] = mysignificand;
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significandParts()[1] = mysignificand2;
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if (myexponent==0) // denormal
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exponent = -1022;
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else
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significandParts()[0] |= 0x10000000000000LL; // integer bit
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if (myexponent2==0)
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exponent2 = -1022;
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else
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significandParts()[1] |= 0x10000000000000LL; // integer bit
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// Unless we have a special case, add in second double.
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if (category == fcNormal) {
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APFloat v(APInt(64, i2));
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fs = v.convert(PPCDoubleDouble, rmNearestTiesToEven, &losesInfo);
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assert(fs == opOK && !losesInfo);
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(void)fs;
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add(v, rmNearestTiesToEven);
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}
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}
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@ -737,4 +737,40 @@ TEST(APFloatTest, convert) {
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EXPECT_EQ(4294967295.0, test.convertToDouble());
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EXPECT_FALSE(losesInfo);
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}
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TEST(APFloatTest, PPCDoubleDouble) {
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APFloat test(APFloat::PPCDoubleDouble, "1.0");
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EXPECT_EQ(0x3ff0000000000000ull, test.bitcastToAPInt().getRawData()[0]);
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EXPECT_EQ(0x0000000000000000ull, test.bitcastToAPInt().getRawData()[1]);
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test.divide(APFloat(APFloat::PPCDoubleDouble, "3.0"), APFloat::rmNearestTiesToEven);
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EXPECT_EQ(0x3fd5555555555555ull, test.bitcastToAPInt().getRawData()[0]);
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EXPECT_EQ(0x3c75555555555556ull, test.bitcastToAPInt().getRawData()[1]);
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// LDBL_MAX
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test = APFloat(APFloat::PPCDoubleDouble, "1.79769313486231580793728971405301e+308");
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EXPECT_EQ(0x7fefffffffffffffull, test.bitcastToAPInt().getRawData()[0]);
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EXPECT_EQ(0x7c8ffffffffffffeull, test.bitcastToAPInt().getRawData()[1]);
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// LDBL_MIN
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test = APFloat(APFloat::PPCDoubleDouble, "2.00416836000897277799610805135016e-292");
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EXPECT_EQ(0x0360000000000000ull, test.bitcastToAPInt().getRawData()[0]);
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EXPECT_EQ(0x0000000000000000ull, test.bitcastToAPInt().getRawData()[1]);
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test = APFloat(APFloat::PPCDoubleDouble, "1.0");
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test.add(APFloat(APFloat::PPCDoubleDouble, "0x1p-105"), APFloat::rmNearestTiesToEven);
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EXPECT_EQ(0x3ff0000000000000ull, test.bitcastToAPInt().getRawData()[0]);
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EXPECT_EQ(0x3960000000000000ull, test.bitcastToAPInt().getRawData()[1]);
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test = APFloat(APFloat::PPCDoubleDouble, "1.0");
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test.add(APFloat(APFloat::PPCDoubleDouble, "0x1p-106"), APFloat::rmNearestTiesToEven);
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EXPECT_EQ(0x3ff0000000000000ull, test.bitcastToAPInt().getRawData()[0]);
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#if 0 // XFAIL
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// This is what we would expect with a true double-double implementation
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EXPECT_EQ(0x3950000000000000ull, test.bitcastToAPInt().getRawData()[1]);
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#else
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// This is what we get with our 106-bit mantissa approximation
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EXPECT_EQ(0x0000000000000000ull, test.bitcastToAPInt().getRawData()[1]);
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#endif
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}
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}
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