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Updated APFloat's comments to fit the LLVM style guide. 

Also added a few more method comments and performed some copy editing.

llvm-svn: 183063
This commit is contained in:
Michael Gottesman 2013-06-01 00:44:05 +00:00
parent a4bc5e1201
commit f033431862
1 changed files with 202 additions and 159 deletions
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361
llvm/include/llvm/ADT/APFloat.h
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@ -6,102 +6,14 @@
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file declares a class to represent arbitrary precision floating
// point values and provide a variety of arithmetic operations on them.
//
///
/// \file
/// \brief
/// This file declares a class to represent arbitrary precision floating point
/// values and provide a variety of arithmetic operations on them.
///
//===----------------------------------------------------------------------===//
/* A self-contained host- and target-independent arbitrary-precision
floating-point software implementation. It uses bignum integer
arithmetic as provided by static functions in the APInt class.
The library will work with bignum integers whose parts are any
unsigned type at least 16 bits wide, but 64 bits is recommended.
Written for clarity rather than speed, in particular with a view
to use in the front-end of a cross compiler so that target
arithmetic can be correctly performed on the host. Performance
should nonetheless be reasonable, particularly for its intended
use. It may be useful as a base implementation for a run-time
library during development of a faster target-specific one.
All 5 rounding modes in the IEEE-754R draft are handled correctly
for all implemented operations. Currently implemented operations
are add, subtract, multiply, divide, fused-multiply-add,
conversion-to-float, conversion-to-integer and
conversion-from-integer. New rounding modes (e.g. away from zero)
can be added with three or four lines of code.
Four formats are built-in: IEEE single precision, double
precision, quadruple precision, and x87 80-bit extended double
(when operating with full extended precision). Adding a new
format that obeys IEEE semantics only requires adding two lines of
code: a declaration and definition of the format.
All operations return the status of that operation as an exception
bit-mask, so multiple operations can be done consecutively with
their results or-ed together. The returned status can be useful
for compiler diagnostics; e.g., inexact, underflow and overflow
can be easily diagnosed on constant folding, and compiler
optimizers can determine what exceptions would be raised by
folding operations and optimize, or perhaps not optimize,
accordingly.
At present, underflow tininess is detected after rounding; it
should be straight forward to add support for the before-rounding
case too.
The library reads hexadecimal floating point numbers as per C99,
and correctly rounds if necessary according to the specified
rounding mode. Syntax is required to have been validated by the
caller. It also converts floating point numbers to hexadecimal
text as per the C99 %a and %A conversions. The output precision
(or alternatively the natural minimal precision) can be specified;
if the requested precision is less than the natural precision the
output is correctly rounded for the specified rounding mode.
It also reads decimal floating point numbers and correctly rounds
according to the specified rounding mode.
Conversion to decimal text is not currently implemented.
Non-zero finite numbers are represented internally as a sign bit,
a 16-bit signed exponent, and the significand as an array of
integer parts. After normalization of a number of precision P the
exponent is within the range of the format, and if the number is
not denormal the P-th bit of the significand is set as an explicit
integer bit. For denormals the most significant bit is shifted
right so that the exponent is maintained at the format's minimum,
so that the smallest denormal has just the least significant bit
of the significand set. The sign of zeroes and infinities is
significant; the exponent and significand of such numbers is not
stored, but has a known implicit (deterministic) value: 0 for the
significands, 0 for zero exponent, all 1 bits for infinity
exponent. For NaNs the sign and significand are deterministic,
although not really meaningful, and preserved in non-conversion
operations. The exponent is implicitly all 1 bits.
APFloat does not provide any exception handling beyond default exception
handling. We represent Signaling NaNs via IEEE-754R 2008 6.2.1 should clause
by encoding Signaling NaNs with the first bit of its trailing significand as
0.
TODO
====
Some features that may or may not be worth adding:
Binary to decimal conversion (hard).
Optional ability to detect underflow tininess before rounding.
New formats: x87 in single and double precision mode (IEEE apart
from extended exponent range) (hard).
New operations: sqrt, IEEE remainder, C90 fmod, nextafter,
nexttoward.
*/
#ifndef LLVM_ADT_APFLOAT_H
#define LLVM_ADT_APFLOAT_H
@ -110,16 +22,17 @@
namespace llvm {
/* Exponents are stored as signed numbers. */
/// A signed type to represent a floating point numbers unbiased exponent.
typedef signed short exponent_t;
struct fltSemantics;
class APSInt;
class StringRef;
/* When bits of a floating point number are truncated, this enum is
used to indicate what fraction of the LSB those bits represented.
It essentially combines the roles of guard and sticky bits. */
/// Enum that represents what fraction of the LSB truncated bits of an fp number
/// represent.
///
/// This essentially combines the roles of guard and sticky bits.
enum lostFraction { // Example of truncated bits:
lfExactlyZero, // 000000
lfLessThanHalf, // 0xxxxx x's not all zero
@ -127,23 +40,109 @@ enum lostFraction { // Example of truncated bits:
lfMoreThanHalf // 1xxxxx x's not all zero
};
/// \brief A self-contained host- and target-independent arbitrary-precision
/// floating-point software implementation.
///
/// APFloat uses bignum integer arithmetic as provided by static functions in
/// the APInt class. The library will work with bignum integers whose parts are
/// any unsigned type at least 16 bits wide, but 64 bits is recommended.
///
/// Written for clarity rather than speed, in particular with a view to use in
/// the front-end of a cross compiler so that target arithmetic can be correctly
/// performed on the host. Performance should nonetheless be reasonable,
/// particularly for its intended use. It may be useful as a base
/// implementation for a run-time library during development of a faster
/// target-specific one.
///
/// All 5 rounding modes in the IEEE-754R draft are handled correctly for all
/// implemented operations. Currently implemented operations are add, subtract,
/// multiply, divide, fused-multiply-add, conversion-to-float,
/// conversion-to-integer and conversion-from-integer. New rounding modes
/// (e.g. away from zero) can be added with three or four lines of code.
///
/// Four formats are built-in: IEEE single precision, double precision,
/// quadruple precision, and x87 80-bit extended double (when operating with
/// full extended precision). Adding a new format that obeys IEEE semantics
/// only requires adding two lines of code: a declaration and definition of the
/// format.
///
/// All operations return the status of that operation as an exception bit-mask,
/// so multiple operations can be done consecutively with their results or-ed
/// together. The returned status can be useful for compiler diagnostics; e.g.,
/// inexact, underflow and overflow can be easily diagnosed on constant folding,
/// and compiler optimizers can determine what exceptions would be raised by
/// folding operations and optimize, or perhaps not optimize, accordingly.
///
/// At present, underflow tininess is detected after rounding; it should be
/// straight forward to add support for the before-rounding case too.
///
/// The library reads hexadecimal floating point numbers as per C99, and
/// correctly rounds if necessary according to the specified rounding mode.
/// Syntax is required to have been validated by the caller. It also converts
/// floating point numbers to hexadecimal text as per the C99 %a and %A
/// conversions. The output precision (or alternatively the natural minimal
/// precision) can be specified; if the requested precision is less than the
/// natural precision the output is correctly rounded for the specified rounding
/// mode.
///
/// It also reads decimal floating point numbers and correctly rounds according
/// to the specified rounding mode.
///
/// Conversion to decimal text is not currently implemented.
///
/// Non-zero finite numbers are represented internally as a sign bit, a 16-bit
/// signed exponent, and the significand as an array of integer parts. After
/// normalization of a number of precision P the exponent is within the range of
/// the format, and if the number is not denormal the P-th bit of the
/// significand is set as an explicit integer bit. For denormals the most
/// significant bit is shifted right so that the exponent is maintained at the
/// format's minimum, so that the smallest denormal has just the least
/// significant bit of the significand set. The sign of zeroes and infinities
/// is significant; the exponent and significand of such numbers is not stored,
/// but has a known implicit (deterministic) value: 0 for the significands, 0
/// for zero exponent, all 1 bits for infinity exponent. For NaNs the sign and
/// significand are deterministic, although not really meaningful, and preserved
/// in non-conversion operations. The exponent is implicitly all 1 bits.
///
/// APFloat does not provide any exception handling beyond default exception
/// handling. We represent Signaling NaNs via IEEE-754R 2008 6.2.1 should clause
/// by encoding Signaling NaNs with the first bit of its trailing significand as
/// 0.
///
/// TODO
/// ====
///
/// Some features that may or may not be worth adding:
///
/// Binary to decimal conversion (hard).
///
/// Optional ability to detect underflow tininess before rounding.
///
/// New formats: x87 in single and double precision mode (IEEE apart from
/// extended exponent range) (hard).
///
/// New operations: sqrt, IEEE remainder, C90 fmod, nextafter, nexttoward.
///
class APFloat {
public:
/* We support the following floating point semantics. */
/// \name Floating Point Semantics.
/// @{
static const fltSemantics IEEEhalf;
static const fltSemantics IEEEsingle;
static const fltSemantics IEEEdouble;
static const fltSemantics IEEEquad;
static const fltSemantics PPCDoubleDouble;
static const fltSemantics x87DoubleExtended;
/* And this pseudo, used to construct APFloats that cannot
conflict with anything real. */
/// A Pseudo fltsemantic used to construct APFloats that cannot conflict with
/// anything real.
static const fltSemantics Bogus;
static unsigned int semanticsPrecision(const fltSemantics &);
/* Floating point numbers have a four-state comparison relation. */
/// IEEE-754R 5.11: Floating Point Comparison Relations.
enum cmpResult {
cmpLessThan,
cmpEqual,
@ -151,7 +150,7 @@ public:
cmpUnordered
};
/* IEEE-754R gives five rounding modes. */
/// IEEE-754R 4.3: Rounding-direction attributes.
enum roundingMode {
rmNearestTiesToEven,
rmTowardPositive,
@ -160,8 +159,9 @@ public:
rmNearestTiesToAway
};
// Operation status. opUnderflow or opOverflow are always returned
// or-ed with opInexact.
/// IEEE-754R 7: Default exception handling.
///
/// opUnderflow or opOverflow are always returned or-ed with opInexact.
enum opStatus {
opOK = 0x00,
opInvalidOp = 0x01,
@ -171,7 +171,7 @@ public:
opInexact = 0x10
};
// Category of internally-represented number.
/// Category of internally-represented number.
enum fltCategory {
fcInfinity,
fcNaN,
@ -179,11 +179,14 @@ public:
fcZero
};
/// Convenience enum used to construct an uninitialized APFloat.
enum uninitializedTag {
uninitialized
};
// Constructors.
/// \name Constructors
/// @{
APFloat(const fltSemantics &); // Default construct to 0.0
APFloat(const fltSemantics &, StringRef);
APFloat(const fltSemantics &, integerPart);
@ -195,7 +198,11 @@ public:
APFloat(const APFloat &);
~APFloat();
// Convenience "constructors"
/// @}
/// \name Convenience "constructors"
/// @{
static APFloat getZero(const fltSemantics &Sem, bool Negative = false) {
return APFloat(Sem, fcZero, Negative);
}
@ -203,7 +210,7 @@ public:
return APFloat(Sem, fcInfinity, Negative);
}
/// getNaN - Factory for QNaN values.
/// Factory for QNaN values.
///
/// \param Negative - True iff the NaN generated should be negative.
/// \param type - The unspecified fill bits for creating the NaN, 0 by
@ -218,75 +225,82 @@ public:
}
}
/// getQNan - Factory for QNaN values.
/// Factory for QNaN values.
static APFloat getQNaN(const fltSemantics &Sem, bool Negative = false,
const APInt *payload = 0) {
return makeNaN(Sem, false, Negative, payload);
}
/// getSNan - Factory for SNaN values.
/// Factory for SNaN values.
static APFloat getSNaN(const fltSemantics &Sem, bool Negative = false,
const APInt *payload = 0) {
return makeNaN(Sem, true, Negative, payload);
}
/// getLargest - Returns the largest finite number in the given
/// semantics.
/// Returns the largest finite number in the given semantics.
///
/// \param Negative - True iff the number should be negative
static APFloat getLargest(const fltSemantics &Sem, bool Negative = false);
/// getSmallest - Returns the smallest (by magnitude) finite number
/// in the given semantics. Might be denormalized, which implies a
/// relative loss of precision.
/// Returns the smallest (by magnitude) finite number in the given semantics.
/// Might be denormalized, which implies a relative loss of precision.
///
/// \param Negative - True iff the number should be negative
static APFloat getSmallest(const fltSemantics &Sem, bool Negative = false);
/// getSmallestNormalized - Returns the smallest (by magnitude)
/// normalized finite number in the given semantics.
/// Returns the smallest (by magnitude) normalized finite number in the given
/// semantics.
///
/// \param Negative - True iff the number should be negative
static APFloat getSmallestNormalized(const fltSemantics &Sem,
bool Negative = false);
/// getAllOnesValue - Returns a float which is bitcasted from
/// an all one value int.
/// Returns a float which is bitcasted from an all one value int.
///
/// \param BitWidth - Select float type
/// \param isIEEE - If 128 bit number, select between PPC and IEEE
static APFloat getAllOnesValue(unsigned BitWidth, bool isIEEE = false);
/// Profile - Used to insert APFloat objects, or objects that contain
/// APFloat objects, into FoldingSets.
/// @}
/// Used to insert APFloat objects, or objects that contain APFloat objects,
/// into FoldingSets.
void Profile(FoldingSetNodeID &NID) const;
/// @brief Used by the Bitcode serializer to emit APInts to Bitcode.
/// \brief Used by the Bitcode serializer to emit APInts to Bitcode.
void Emit(Serializer &S) const;
/// @brief Used by the Bitcode deserializer to deserialize APInts.
/// \brief Used by the Bitcode deserializer to deserialize APInts.
static APFloat ReadVal(Deserializer &D);
/* Arithmetic. */
/// \name Arithmetic
/// @{
opStatus add(const APFloat &, roundingMode);
opStatus subtract(const APFloat &, roundingMode);
opStatus multiply(const APFloat &, roundingMode);
opStatus divide(const APFloat &, roundingMode);
/* IEEE remainder. */
/// IEEE remainder.
opStatus remainder(const APFloat &);
/* C fmod, or llvm frem. */
/// C fmod, or llvm frem.
opStatus mod(const APFloat &, roundingMode);
opStatus fusedMultiplyAdd(const APFloat &, const APFloat &, roundingMode);
opStatus roundToIntegral(roundingMode);
/// IEEE-754R 5.3.1: nextUp/nextDown.
opStatus next(bool nextDown);
/* Sign operations. */
/// \name Sign operations.
/// @{
void changeSign();
void clearSign();
void copySign(const APFloat &);
/* Conversions. */
/// @}
/// \name Conversions
/// @{
opStatus convert(const fltSemantics &, roundingMode, bool *);
opStatus convertToInteger(integerPart *, unsigned int, bool, roundingMode,
bool *) const;
@ -301,26 +315,29 @@ public:
double convertToDouble() const;
float convertToFloat() const;
/* The definition of equality is not straightforward for floating point,
so we won't use operator==. Use one of the following, or write
whatever it is you really mean. */
/// @}
/// The definition of equality is not straightforward for floating point, so
/// we won't use operator==. Use one of the following, or write whatever it
/// is you really mean.
bool operator==(const APFloat &) const LLVM_DELETED_FUNCTION;
/* IEEE comparison with another floating point number (NaNs
compare unordered, 0==-0). */
/// IEEE comparison with another floating point number (NaNs compare
/// unordered, 0==-0).
cmpResult compare(const APFloat &) const;
/* Bitwise comparison for equality (QNaNs compare equal, 0!=-0). */
/// Bitwise comparison for equality (QNaNs compare equal, 0!=-0).
bool bitwiseIsEqual(const APFloat &) const;
/* Write out a hexadecimal representation of the floating point
value to DST, which must be of sufficient size, in the C99 form
[-]0xh.hhhhp[+-]d. Return the number of characters written,
excluding the terminating NUL. */
/// Write out a hexadecimal representation of the floating point value to DST,
/// which must be of sufficient size, in the C99 form [-]0xh.hhhhp[+-]d.
/// Return the number of characters written, excluding the terminating NUL.
unsigned int convertToHexString(char *dst, unsigned int hexDigits,
bool upperCase, roundingMode) const;
/* Simple queries. */
/// \name Simple Queries
/// @{
fltCategory getCategory() const { return category; }
const fltSemantics &getSemantics() const { return *semantics; }
bool isZero() const { return category == fcZero; }
@ -335,6 +352,8 @@ public:
/// IEEE-754R 5.7.2: isSignaling. Returns true if this is a signaling NaN.
bool isSignaling() const;
/// @}
APFloat &operator=(const APFloat &);
/// \brief Overload to compute a hash code for an APFloat value.
@ -371,18 +390,24 @@ public:
void toString(SmallVectorImpl<char> &Str, unsigned FormatPrecision = 0,
unsigned FormatMaxPadding = 3) const;
/// getExactInverse - If this value has an exact multiplicative inverse,
/// store it in inv and return true.
/// If this value has an exact multiplicative inverse, store it in inv and
/// return true.
bool getExactInverse(APFloat *inv) const;
private:
/* Trivial queries. */
/// \name Simple Queries
/// @{
integerPart *significandParts();
const integerPart *significandParts() const;
unsigned int partCount() const;
/* Significand operations. */
/// @}
/// \name Significand operations.
/// @{
integerPart addSignificand(const APFloat &);
integerPart subtractSignificand(const APFloat &, integerPart);
lostFraction addOrSubtractSignificand(const APFloat &, bool subtract);
@ -400,19 +425,29 @@ private:
/// Return true if the significand excluding the integral bit is all zeros.
bool isSignificandAllZeros() const;
/* Arithmetic on special values. */
/// @}
/// \name Arithmetic on special values.
/// @{
opStatus addOrSubtractSpecials(const APFloat &, bool subtract);
opStatus divideSpecials(const APFloat &);
opStatus multiplySpecials(const APFloat &);
opStatus modSpecials(const APFloat &);
/* Set to special values. */
/// @}
/// \name Special value setters.
/// @{
void makeLargest(bool Neg = false);
void makeSmallest(bool Neg = false);
void makeNaN(bool SNaN = false, bool Neg = false, const APInt *fill = 0);
static APFloat makeNaN(const fltSemantics &Sem, bool SNaN, bool Negative,
const APInt *fill);
/// @}
/// \name Special value queries only useful internally to APFloat
/// @{
@ -425,7 +460,9 @@ private:
/// @}
/* Miscellany. */
/// \name Miscellany
/// @{
opStatus normalize(roundingMode, lostFraction);
opStatus addOrSubtract(const APFloat &, roundingMode, bool subtract);
cmpResult compareAbsoluteValue(const APFloat &) const;
@ -442,6 +479,8 @@ private:
opStatus roundSignificandWithExponent(const integerPart *, unsigned int, int,
roundingMode);
/// @}
APInt convertHalfAPFloatToAPInt() const;
APInt convertFloatAPFloatToAPInt() const;
APInt convertDoubleAPFloatToAPInt() const;
@ -460,31 +499,35 @@ private:
void copySignificand(const APFloat &);
void freeSignificand();
/* What kind of semantics does this value obey? */
/// The semantics that this value obeys.
const fltSemantics *semantics;
/* Significand - the fraction with an explicit integer bit. Must be
at least one bit wider than the target precision. */
/// A binary fraction with an explicit integer bit.
///
/// The significand must be at least one bit wider than the target precision.
union Significand {
integerPart part;
integerPart *parts;
} significand;
/* The exponent - a signed number. */
/// The signed unbiased exponent of the value.
exponent_t exponent;
/* What kind of floating point number this is. */
/* Only 2 bits are required, but VisualStudio incorrectly sign extends
it. Using the extra bit keeps it from failing under VisualStudio */
/// What kind of floating point number this is.
///
/// Only 2 bits are required, but VisualStudio incorrectly sign extends it.
/// Using the extra bit keeps it from failing under VisualStudio.
fltCategory category : 3;
/* The sign bit of this number. */
/// Sign bit of the number.
unsigned int sign : 1;
};
// See friend declaration above. This additional declaration is required in
// order to compile LLVM with IBM xlC compiler.
/// See friend declaration above.
///
/// This additional declaration is required in order to compile LLVM with IBM
/// xlC compiler.
hash_code hash_value(const APFloat &Arg);
} /* namespace llvm */
} // namespace llvm
#endif /* LLVM_ADT_APFLOAT_H */
#endif // LLVM_ADT_APFLOAT_H