| //== llvm/Support/APFloat.h - Arbitrary Precision Floating Point -*- C++ -*-==// |
| // |
| // The LLVM Compiler Infrastructure |
| // |
| // This file was developed by Neil Booth and is distributed under the |
| // University of Illinois Open Source 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. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| /* 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. |
| |
| 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_FLOAT_H |
| #define LLVM_FLOAT_H |
| |
| // APInt contains static functions implementing bignum arithmetic. |
| #include "llvm/ADT/APInt.h" |
| |
| namespace llvm { |
| |
| /* Exponents are stored as signed numbers. */ |
| typedef signed short exponent_t; |
| |
| struct fltSemantics; |
| |
| /* 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 lostFraction { // Example of truncated bits: |
| lfExactlyZero, // 000000 |
| lfLessThanHalf, // 0xxxxx x's not all zero |
| lfExactlyHalf, // 100000 |
| lfMoreThanHalf // 1xxxxx x's not all zero |
| }; |
| |
| class APFloat { |
| public: |
| |
| /* We support the following floating point semantics. */ |
| static const fltSemantics IEEEsingle; |
| static const fltSemantics IEEEdouble; |
| static const fltSemantics IEEEquad; |
| static const fltSemantics PPCDoubleDouble; |
| static const fltSemantics x87DoubleExtended; |
| /* And this psuedo, 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. */ |
| enum cmpResult { |
| cmpLessThan, |
| cmpEqual, |
| cmpGreaterThan, |
| cmpUnordered |
| }; |
| |
| /* IEEE-754R gives five rounding modes. */ |
| enum roundingMode { |
| rmNearestTiesToEven, |
| rmTowardPositive, |
| rmTowardNegative, |
| rmTowardZero, |
| rmNearestTiesToAway |
| }; |
| |
| /* Operation status. opUnderflow or opOverflow are always returned |
| or-ed with opInexact. */ |
| enum opStatus { |
| opOK = 0x00, |
| opInvalidOp = 0x01, |
| opDivByZero = 0x02, |
| opOverflow = 0x04, |
| opUnderflow = 0x08, |
| opInexact = 0x10 |
| }; |
| |
| /* Category of internally-represented number. */ |
| enum fltCategory { |
| fcInfinity, |
| fcNaN, |
| fcNormal, |
| fcZero |
| }; |
| |
| /* Constructors. */ |
| APFloat(const fltSemantics &, const char *); |
| APFloat(const fltSemantics &, integerPart); |
| APFloat(const fltSemantics &, fltCategory, bool negative); |
| explicit APFloat(double d); |
| explicit APFloat(float f); |
| explicit APFloat(const APInt &, bool isIEEE = false); |
| APFloat(const APFloat &); |
| ~APFloat(); |
| |
| /// @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. |
| static APFloat ReadVal(Deserializer& D); |
| |
| /* Arithmetic. */ |
| opStatus add(const APFloat &, roundingMode); |
| opStatus subtract(const APFloat &, roundingMode); |
| opStatus multiply(const APFloat &, roundingMode); |
| opStatus divide(const APFloat &, roundingMode); |
| opStatus mod(const APFloat &, roundingMode); |
| opStatus fusedMultiplyAdd(const APFloat &, const APFloat &, roundingMode); |
| |
| /* Sign operations. */ |
| void changeSign(); |
| void clearSign(); |
| void copySign(const APFloat &); |
| |
| /* Conversions. */ |
| opStatus convert(const fltSemantics &, roundingMode); |
| opStatus convertToInteger(integerPart *, unsigned int, bool, |
| roundingMode) const; |
| opStatus convertFromSignExtendedInteger(const integerPart *, unsigned int, |
| bool, roundingMode); |
| opStatus convertFromZeroExtendedInteger(const integerPart *, unsigned int, |
| bool, roundingMode); |
| opStatus convertFromString(const char *, roundingMode); |
| APInt convertToAPInt() const; |
| 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. */ |
| // bool operator==(const APFloat &) const; // DO NOT IMPLEMENT |
| |
| /* IEEE comparison with another floating point number (NaNs |
| compare unordered, 0==-0). */ |
| cmpResult compare(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. */ |
| unsigned int convertToHexString(char *dst, unsigned int hexDigits, |
| bool upperCase, roundingMode) const; |
| |
| /* Bitwise comparison for equality (QNaNs compare equal, 0!=-0). */ |
| bool bitwiseIsEqual(const APFloat &) const; |
| |
| /* Simple queries. */ |
| fltCategory getCategory() const { return category; } |
| const fltSemantics &getSemantics() const { return *semantics; } |
| bool isZero() const { return category == fcZero; } |
| bool isNonZero() const { return category != fcZero; } |
| bool isNaN() const { return category == fcNaN; } |
| bool isNegative() const { return sign; } |
| bool isPosZero() const { return isZero() && !isNegative(); } |
| bool isNegZero() const { return isZero() && isNegative(); } |
| |
| APFloat& operator=(const APFloat &); |
| |
| /* Return an arbitrary integer value usable for hashing. */ |
| uint32_t getHashValue() const; |
| |
| private: |
| |
| /* Trivial queries. */ |
| integerPart *significandParts(); |
| const integerPart *significandParts() const; |
| unsigned int partCount() const; |
| |
| /* Significand operations. */ |
| integerPart addSignificand(const APFloat &); |
| integerPart subtractSignificand(const APFloat &, integerPart); |
| lostFraction addOrSubtractSignificand(const APFloat &, bool subtract); |
| lostFraction multiplySignificand(const APFloat &, const APFloat *); |
| lostFraction divideSignificand(const APFloat &); |
| void incrementSignificand(); |
| void initialize(const fltSemantics *); |
| void shiftSignificandLeft(unsigned int); |
| lostFraction shiftSignificandRight(unsigned int); |
| unsigned int significandLSB() const; |
| unsigned int significandMSB() const; |
| void zeroSignificand(); |
| |
| /* Arithmetic on special values. */ |
| opStatus addOrSubtractSpecials(const APFloat &, bool subtract); |
| opStatus divideSpecials(const APFloat &); |
| opStatus multiplySpecials(const APFloat &); |
| |
| /* Miscellany. */ |
| void makeNaN(void); |
| opStatus normalize(roundingMode, lostFraction); |
| opStatus addOrSubtract(const APFloat &, roundingMode, bool subtract); |
| 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); |
| opStatus convertFromDecimalString (const char *, roundingMode); |
| char *convertNormalToHexString(char *, unsigned int, bool, |
| roundingMode) const; |
| opStatus roundSignificandWithExponent(const integerPart *, unsigned int, |
| int, roundingMode); |
| |
| APInt convertFloatAPFloatToAPInt() const; |
| APInt convertDoubleAPFloatToAPInt() const; |
| APInt convertF80LongDoubleAPFloatToAPInt() const; |
| APInt convertPPCDoubleDoubleAPFloatToAPInt() const; |
| void initFromAPInt(const APInt& api, bool isIEEE = false); |
| void initFromFloatAPInt(const APInt& api); |
| void initFromDoubleAPInt(const APInt& api); |
| void initFromF80LongDoubleAPInt(const APInt& api); |
| void initFromPPCDoubleDoubleAPInt(const APInt& api); |
| |
| void assign(const APFloat &); |
| void copySignificand(const APFloat &); |
| void freeSignificand(); |
| |
| /* What kind of semantics does this value obey? */ |
| const fltSemantics *semantics; |
| |
| /* Significand - the fraction with an explicit integer bit. Must be |
| at least one bit wider than the target precision. */ |
| union Significand |
| { |
| integerPart part; |
| integerPart *parts; |
| } significand; |
| |
| /* The exponent - a signed number. */ |
| 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 */ |
| fltCategory category: 3; |
| |
| /* The sign bit of this number. */ |
| unsigned int sign: 1; |
| |
| /* For PPCDoubleDouble, we have a second exponent and sign (the second |
| significand is appended to the first one, although it would be wrong to |
| regard these as a single number for arithmetic purposes). These fields |
| are not meaningful for any other type. */ |
| exponent_t exponent2 : 11; |
| unsigned int sign2: 1; |
| }; |
| } /* namespace llvm */ |
| |
| #endif /* LLVM_FLOAT_H */ |
