+APFloat::APFloat(double d) {
+ initFromAPInt(APInt::doubleToBits(d));
+}
+
+namespace {
+ void append(SmallVectorImpl<char> &Buffer, StringRef Str) {
+ Buffer.append(Str.begin(), Str.end());
+ }
+
+ /// Removes data from the given significand until it is no more
+ /// precise than is required for the desired precision.
+ void AdjustToPrecision(APInt &significand,
+ int &exp, unsigned FormatPrecision) {
+ unsigned bits = significand.getActiveBits();
+
+ // 196/59 is a very slight overestimate of lg_2(10).
+ unsigned bitsRequired = (FormatPrecision * 196 + 58) / 59;
+
+ if (bits <= bitsRequired) return;
+
+ unsigned tensRemovable = (bits - bitsRequired) * 59 / 196;
+ if (!tensRemovable) return;
+
+ exp += tensRemovable;
+
+ APInt divisor(significand.getBitWidth(), 1);
+ APInt powten(significand.getBitWidth(), 10);
+ while (true) {
+ if (tensRemovable & 1)
+ divisor *= powten;
+ tensRemovable >>= 1;
+ if (!tensRemovable) break;
+ powten *= powten;
+ }
+
+ significand = significand.udiv(divisor);
+
+ // Truncate the significand down to its active bit count, but
+ // don't try to drop below 32.
+ unsigned newPrecision = std::max(32U, significand.getActiveBits());
+ significand = significand.trunc(newPrecision);
+ }
+
+
+ void AdjustToPrecision(SmallVectorImpl<char> &buffer,
+ int &exp, unsigned FormatPrecision) {
+ unsigned N = buffer.size();
+ if (N <= FormatPrecision) return;
+
+ // The most significant figures are the last ones in the buffer.
+ unsigned FirstSignificant = N - FormatPrecision;
+
+ // Round.
+ // FIXME: this probably shouldn't use 'round half up'.
+
+ // Rounding down is just a truncation, except we also want to drop
+ // trailing zeros from the new result.
+ if (buffer[FirstSignificant - 1] < '5') {
+ while (FirstSignificant < N && buffer[FirstSignificant] == '0')
+ FirstSignificant++;
+
+ exp += FirstSignificant;
+ buffer.erase(&buffer[0], &buffer[FirstSignificant]);
+ return;
+ }
+
+ // Rounding up requires a decimal add-with-carry. If we continue
+ // the carry, the newly-introduced zeros will just be truncated.
+ for (unsigned I = FirstSignificant; I != N; ++I) {
+ if (buffer[I] == '9') {
+ FirstSignificant++;
+ } else {
+ buffer[I]++;
+ break;
+ }
+ }
+
+ // If we carried through, we have exactly one digit of precision.
+ if (FirstSignificant == N) {
+ exp += FirstSignificant;
+ buffer.clear();
+ buffer.push_back('1');
+ return;
+ }
+
+ exp += FirstSignificant;
+ buffer.erase(&buffer[0], &buffer[FirstSignificant]);
+ }
+}
+
+void APFloat::toString(SmallVectorImpl<char> &Str,
+ unsigned FormatPrecision,
+ unsigned FormatMaxPadding) const {
+ switch (category) {
+ case fcInfinity:
+ if (isNegative())
+ return append(Str, "-Inf");
+ else
+ return append(Str, "+Inf");
+
+ case fcNaN: return append(Str, "NaN");
+
+ case fcZero:
+ if (isNegative())
+ Str.push_back('-');
+
+ if (!FormatMaxPadding)
+ append(Str, "0.0E+0");
+ else
+ Str.push_back('0');
+ return;
+
+ case fcNormal:
+ break;
+ }
+
+ if (isNegative())
+ Str.push_back('-');
+
+ // Decompose the number into an APInt and an exponent.
+ int exp = exponent - ((int) semantics->precision - 1);
+ APInt significand(semantics->precision,
+ makeArrayRef(significandParts(),
+ partCountForBits(semantics->precision)));
+
+ // Set FormatPrecision if zero. We want to do this before we
+ // truncate trailing zeros, as those are part of the precision.
+ if (!FormatPrecision) {
+ // It's an interesting question whether to use the nominal
+ // precision or the active precision here for denormals.
+
+ // FormatPrecision = ceil(significandBits / lg_2(10))
+ FormatPrecision = (semantics->precision * 59 + 195) / 196;
+ }
+
+ // Ignore trailing binary zeros.
+ int trailingZeros = significand.countTrailingZeros();
+ exp += trailingZeros;
+ significand = significand.lshr(trailingZeros);
+
+ // Change the exponent from 2^e to 10^e.
+ if (exp == 0) {
+ // Nothing to do.
+ } else if (exp > 0) {
+ // Just shift left.
+ significand = significand.zext(semantics->precision + exp);
+ significand <<= exp;
+ exp = 0;
+ } else { /* exp < 0 */
+ int texp = -exp;
+
+ // We transform this using the identity:
+ // (N)(2^-e) == (N)(5^e)(10^-e)
+ // This means we have to multiply N (the significand) by 5^e.
+ // To avoid overflow, we have to operate on numbers large
+ // enough to store N * 5^e:
+ // log2(N * 5^e) == log2(N) + e * log2(5)
+ // <= semantics->precision + e * 137 / 59
+ // (log_2(5) ~ 2.321928 < 2.322034 ~ 137/59)
+
+ unsigned precision = semantics->precision + (137 * texp + 136) / 59;
+
+ // Multiply significand by 5^e.
+ // N * 5^0101 == N * 5^(1*1) * 5^(0*2) * 5^(1*4) * 5^(0*8)
+ significand = significand.zext(precision);
+ APInt five_to_the_i(precision, 5);
+ while (true) {
+ if (texp & 1) significand *= five_to_the_i;
+
+ texp >>= 1;
+ if (!texp) break;
+ five_to_the_i *= five_to_the_i;
+ }
+ }
+
+ AdjustToPrecision(significand, exp, FormatPrecision);
+
+ llvm::SmallVector<char, 256> buffer;
+
+ // Fill the buffer.
+ unsigned precision = significand.getBitWidth();
+ APInt ten(precision, 10);
+ APInt digit(precision, 0);
+
+ bool inTrail = true;
+ while (significand != 0) {
+ // digit <- significand % 10
+ // significand <- significand / 10
+ APInt::udivrem(significand, ten, significand, digit);
+
+ unsigned d = digit.getZExtValue();
+
+ // Drop trailing zeros.
+ if (inTrail && !d) exp++;
+ else {
+ buffer.push_back((char) ('0' + d));
+ inTrail = false;
+ }
+ }
+
+ assert(!buffer.empty() && "no characters in buffer!");
+
+ // Drop down to FormatPrecision.
+ // TODO: don't do more precise calculations above than are required.
+ AdjustToPrecision(buffer, exp, FormatPrecision);
+
+ unsigned NDigits = buffer.size();
+
+ // Check whether we should use scientific notation.
+ bool FormatScientific;
+ if (!FormatMaxPadding)
+ FormatScientific = true;
+ else {
+ if (exp >= 0) {
+ // 765e3 --> 765000
+ // ^^^
+ // But we shouldn't make the number look more precise than it is.
+ FormatScientific = ((unsigned) exp > FormatMaxPadding ||
+ NDigits + (unsigned) exp > FormatPrecision);
+ } else {
+ // Power of the most significant digit.
+ int MSD = exp + (int) (NDigits - 1);
+ if (MSD >= 0) {
+ // 765e-2 == 7.65
+ FormatScientific = false;
+ } else {
+ // 765e-5 == 0.00765
+ // ^ ^^
+ FormatScientific = ((unsigned) -MSD) > FormatMaxPadding;
+ }
+ }
+ }
+
+ // Scientific formatting is pretty straightforward.
+ if (FormatScientific) {
+ exp += (NDigits - 1);
+
+ Str.push_back(buffer[NDigits-1]);
+ Str.push_back('.');
+ if (NDigits == 1)
+ Str.push_back('0');
+ else
+ for (unsigned I = 1; I != NDigits; ++I)
+ Str.push_back(buffer[NDigits-1-I]);
+ Str.push_back('E');
+
+ Str.push_back(exp >= 0 ? '+' : '-');
+ if (exp < 0) exp = -exp;
+ SmallVector<char, 6> expbuf;
+ do {
+ expbuf.push_back((char) ('0' + (exp % 10)));
+ exp /= 10;
+ } while (exp);
+ for (unsigned I = 0, E = expbuf.size(); I != E; ++I)
+ Str.push_back(expbuf[E-1-I]);
+ return;
+ }
+
+ // Non-scientific, positive exponents.
+ if (exp >= 0) {
+ for (unsigned I = 0; I != NDigits; ++I)
+ Str.push_back(buffer[NDigits-1-I]);
+ for (unsigned I = 0; I != (unsigned) exp; ++I)
+ Str.push_back('0');
+ return;
+ }
+
+ // Non-scientific, negative exponents.
+
+ // The number of digits to the left of the decimal point.
+ int NWholeDigits = exp + (int) NDigits;
+
+ unsigned I = 0;
+ if (NWholeDigits > 0) {
+ for (; I != (unsigned) NWholeDigits; ++I)
+ Str.push_back(buffer[NDigits-I-1]);
+ Str.push_back('.');
+ } else {
+ unsigned NZeros = 1 + (unsigned) -NWholeDigits;
+
+ Str.push_back('0');
+ Str.push_back('.');
+ for (unsigned Z = 1; Z != NZeros; ++Z)
+ Str.push_back('0');
+ }
+
+ for (; I != NDigits; ++I)
+ Str.push_back(buffer[NDigits-I-1]);
+}
+
+bool APFloat::getExactInverse(APFloat *inv) const {
+ // Special floats and denormals have no exact inverse.
+ if (category != fcNormal)
+ return false;
+
+ // Check that the number is a power of two by making sure that only the
+ // integer bit is set in the significand.
+ if (significandLSB() != semantics->precision - 1)
+ return false;
+
+ // Get the inverse.
+ APFloat reciprocal(*semantics, 1ULL);
+ if (reciprocal.divide(*this, rmNearestTiesToEven) != opOK)
+ return false;
+
+ // Avoid multiplication with a denormal, it is not safe on all platforms and
+ // may be slower than a normal division.
+ if (reciprocal.significandMSB() + 1 < reciprocal.semantics->precision)
+ return false;
+
+ assert(reciprocal.category == fcNormal &&
+ reciprocal.significandLSB() == reciprocal.semantics->precision - 1);
+
+ if (inv)
+ *inv = reciprocal;
+
+ return true;
projects / oota-llvm.git / blobdiff