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When converting to integer, do bit manipulations in the destination

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memory rather than in a copy of the APFloat.  This avoids problems
when the destination is wider than our significand and is cleaner.

Also provide deterministic values in all cases where conversion
fails, namely zero for NaNs and the minimal or maximal value
respectively for underflow or overflow.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@43626 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Neil Booth 2007-11-01 22:43:37 +00:00
parent ff37ccc570
commit ee7ae384f5
2 changed files with 121 additions and 83 deletions
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2
include/llvm/ADT/APFloat.h
View File

@ -275,6 +275,8 @@ namespace llvm {
cmpResult compareAbsoluteValue(const APFloat &) const;
opStatus handleOverflow(roundingMode);
bool roundAwayFromZero(roundingMode, lostFraction, unsigned int) const;
opStatus convertToSignExtendedInteger(integerPart *, unsigned int, bool,
roundingMode) const;
opStatus convertFromUnsignedParts(const integerPart *, unsigned int,
roundingMode);
opStatus convertFromHexadecimalString(const char *, roundingMode);

202
lib/Support/APFloat.cpp
View File

@ -1733,7 +1733,8 @@ APFloat::convert(const fltSemantics &toSemantics,
/* Convert a floating point number to an integer according to the
rounding mode. If the rounded integer value is out of range this
returns an invalid operation exception. If the rounded value is in
returns an invalid operation exception and the contents of the
destination parts are unspecified. If the rounded value is in
range but the floating point number is not the exact integer, the C
standard doesn't require an inexact exception to be raised. IEEE
854 does require it so we do that.
@ -1741,95 +1742,131 @@ APFloat::convert(const fltSemantics &toSemantics,
Note that for conversions to integer type the C standard requires
round-to-zero to always be used. */
APFloat::opStatus
APFloat::convertToSignExtendedInteger(integerPart *parts, unsigned int width,
bool isSigned,
roundingMode rounding_mode) const
{
lostFraction lost_fraction;
const integerPart *src;
unsigned int dstPartsCount, truncatedBits;
/* Handle the three special cases first. */
if(category == fcInfinity || category == fcNaN)
return opInvalidOp;
dstPartsCount = partCountForBits(width);
if(category == fcZero) {
APInt::tcSet(parts, 0, dstPartsCount);
return opOK;
}
src = significandParts();
/* Step 1: place our absolute value, with any fraction truncated, in
the destination. */
if (exponent < 0) {
/* Our absolute value is less than one; truncate everything. */
APInt::tcSet(parts, 0, dstPartsCount);
truncatedBits = semantics->precision;
} else {
/* We want the most significant (exponent + 1) bits; the rest are
truncated. */
unsigned int bits = exponent + 1U;
/* Hopelessly large in magnitude? */
if (bits > width)
return opInvalidOp;
if (bits < semantics->precision) {
/* We truncate (semantics->precision - bits) bits. */
truncatedBits = semantics->precision - bits;
APInt::tcExtract(parts, dstPartsCount, src, bits, truncatedBits);
} else {
/* We want at least as many bits as are available. */
APInt::tcExtract(parts, dstPartsCount, src, semantics->precision, 0);
APInt::tcShiftLeft(parts, dstPartsCount, bits - semantics->precision);
truncatedBits = 0;
}
}
/* Step 2: work out any lost fraction, and increment the absolute
value if we would round away from zero. */
if (truncatedBits) {
lost_fraction = lostFractionThroughTruncation(src, partCount(),
truncatedBits);
if (lost_fraction != lfExactlyZero
&& roundAwayFromZero(rounding_mode, lost_fraction, truncatedBits)) {
if (APInt::tcIncrement(parts, dstPartsCount))
return opInvalidOp; /* Overflow. */
}
} else {
lost_fraction = lfExactlyZero;
}
/* Step 3: check if we fit in the destination. */
unsigned int omsb = APInt::tcMSB(parts, dstPartsCount) + 1;
if (sign) {
if (!isSigned) {
/* Negative numbers cannot be represented as unsigned. */
if (omsb != 0)
return opInvalidOp;
} else {
/* It takes omsb bits to represent the unsigned integer value.
We lose a bit for the sign, but care is needed as the
maximally negative integer is a special case. */
if (omsb == width && APInt::tcLSB(parts, dstPartsCount) + 1 != omsb)
return opInvalidOp;
/* This case can happen because of rounding. */
if (omsb > width)
return opInvalidOp;
}
APInt::tcNegate (parts, dstPartsCount);
} else {
if (omsb >= width + !isSigned)
return opInvalidOp;
}
if (lost_fraction == lfExactlyZero)
return opOK;
else
return opInexact;
}
/* Same as convertToSignExtendedInteger, except we provide
deterministic values in case of an invalid operation exception,
namely zero for NaNs and the minimal or maximal value respectively
for underflow or overflow. */
APFloat::opStatus
APFloat::convertToInteger(integerPart *parts, unsigned int width,
bool isSigned,
roundingMode rounding_mode) const
{
lostFraction lost_fraction;
unsigned int msb, partsCount;
int bits;
opStatus fs;
assertArithmeticOK(*semantics);
partsCount = partCountForBits(width);
fs = convertToSignExtendedInteger(parts, width, isSigned, rounding_mode);
/* Handle the three special cases first. We produce
a deterministic result even for the Invalid cases. */
if (category == fcNaN) {
// Neither sign nor isSigned affects this.
APInt::tcSet(parts, 0, partsCount);
return opInvalidOp;
}
if (category == fcInfinity) {
if (!sign && isSigned)
APInt::tcSetLeastSignificantBits(parts, partsCount, width-1);
else if (!sign && !isSigned)
APInt::tcSetLeastSignificantBits(parts, partsCount, width);
else if (sign && isSigned) {
APInt::tcSetLeastSignificantBits(parts, partsCount, 1);
APInt::tcShiftLeft(parts, partsCount, width-1);
} else // sign && !isSigned
APInt::tcSet(parts, 0, partsCount);
return opInvalidOp;
}
if (category == fcZero) {
APInt::tcSet(parts, 0, partsCount);
return opOK;
if (fs == opInvalidOp) {
unsigned int bits, dstPartsCount;
dstPartsCount = partCountForBits(width);
if (category == fcNaN)
bits = 0;
else if (sign)
bits = isSigned;
else
bits = width - isSigned;
APInt::tcSetLeastSignificantBits(parts, dstPartsCount, bits);
if (sign && isSigned)
APInt::tcShiftLeft(parts, dstPartsCount, width - 1);
}
/* Shift the bit pattern so the fraction is lost. */
APFloat tmp(*this);
bits = (int) semantics->precision - 1 - exponent;
if(bits > 0) {
lost_fraction = tmp.shiftSignificandRight(bits);
} else {
if ((unsigned) -bits >= semantics->precision) {
// Unrepresentably large.
if (!sign && isSigned)
APInt::tcSetLeastSignificantBits(parts, partsCount, width-1);
else if (!sign && !isSigned)
APInt::tcSetLeastSignificantBits(parts, partsCount, width);
else if (sign && isSigned) {
APInt::tcSetLeastSignificantBits(parts, partsCount, 1);
APInt::tcShiftLeft(parts, partsCount, width-1);
} else // sign && !isSigned
APInt::tcSet(parts, 0, partsCount);
return (opStatus)(opOverflow | opInexact);
}
tmp.shiftSignificandLeft(-bits);
lost_fraction = lfExactlyZero;
}
if(lost_fraction != lfExactlyZero
&& tmp.roundAwayFromZero(rounding_mode, lost_fraction, 0))
tmp.incrementSignificand();
msb = tmp.significandMSB();
/* Negative numbers cannot be represented as unsigned. */
if(!isSigned && tmp.sign && msb != -1U)
return opInvalidOp;
/* It takes exponent + 1 bits to represent the truncated floating
point number without its sign. We lose a bit for the sign, but
the maximally negative integer is a special case. */
if(msb + 1 > width) /* !! Not same as msb >= width !! */
return opInvalidOp;
if(isSigned && msb + 1 == width
&& (!tmp.sign || tmp.significandLSB() != msb))
return opInvalidOp;
APInt::tcAssign(parts, tmp.significandParts(), partsCount);
if(tmp.sign)
APInt::tcNegate(parts, partsCount);
if(lost_fraction == lfExactlyZero)
return opOK;
else
return opInexact;
return fs;
}
/* Convert an unsigned integer SRC to a floating point number,
@ -2162,7 +2199,6 @@ APFloat::convertFromDecimalString(const char *p, roundingMode rounding_mode)
partCount++;
} while (p <= D.lastSigDigit);
category = fcNormal;
fs = roundSignificandWithExponent(decSignificand, partCount,
D.exponent, rounding_mode);