1 //== llvm/Support/APFloat.h - Arbitrary Precision Floating Point -*- C++ -*-==//
3 // The LLVM Compiler Infrastructure
5 // This file was developed by Neil Booth and is distributed under the
6 // University of Illinois Open Source License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file declares a class to represent arbitrary precision floating
11 // point values and provide a variety of arithmetic operations on them.
13 //===----------------------------------------------------------------------===//
15 /* A self-contained host- and target-independent arbitrary-precision
16 floating-point software implementation. It uses bignum integer
17 arithmetic as provided by static functions in the APInt class.
18 The library will work with bignum integers whose parts are any
19 unsigned type at least 16 bits wide, but 64 bits is recommended.
21 Written for clarity rather than speed, in particular with a view
22 to use in the front-end of a cross compiler so that target
23 arithmetic can be correctly performed on the host. Performance
24 should nonetheless be reasonable, particularly for its intended
25 use. It may be useful as a base implementation for a run-time
26 library during development of a faster target-specific one.
28 All 5 rounding modes in the IEEE-754R draft are handled correctly
29 for all implemented operations. Currently implemented operations
30 are add, subtract, multiply, divide, fused-multiply-add,
31 conversion-to-float, conversion-to-integer and
32 conversion-from-integer. New rounding modes (e.g. away from zero)
33 can be added with three or four lines of code.
35 Four formats are built-in: IEEE single precision, double
36 precision, quadruple precision, and x87 80-bit extended double
37 (when operating with full extended precision). Adding a new
38 format that obeys IEEE semantics only requires adding two lines of
39 code: a declaration and definition of the format.
41 All operations return the status of that operation as an exception
42 bit-mask, so multiple operations can be done consecutively with
43 their results or-ed together. The returned status can be useful
44 for compiler diagnostics; e.g., inexact, underflow and overflow
45 can be easily diagnosed on constant folding, and compiler
46 optimizers can determine what exceptions would be raised by
47 folding operations and optimize, or perhaps not optimize,
50 At present, underflow tininess is detected after rounding; it
51 should be straight forward to add support for the before-rounding
54 The library reads hexadecimal floating point numbers as per C99,
55 and correctly rounds if necessary according to the specified
56 rounding mode. Syntax is required to have been validated by the
57 caller. It also converts floating point numbers to hexadecimal
58 text as per the C99 %a and %A conversions. The output precision
59 (or alternatively the natural minimal precision) can be specified;
60 if the requested precision is less than the natural precision the
61 output is correctly rounded for the specified rounding mode.
63 It also reads decimal floating point numbers and correctly rounds
64 according to the specified rounding mode.
66 Conversion to decimal text is not currently implemented.
68 Non-zero finite numbers are represented internally as a sign bit,
69 a 16-bit signed exponent, and the significand as an array of
70 integer parts. After normalization of a number of precision P the
71 exponent is within the range of the format, and if the number is
72 not denormal the P-th bit of the significand is set as an explicit
73 integer bit. For denormals the most significant bit is shifted
74 right so that the exponent is maintained at the format's minimum,
75 so that the smallest denormal has just the least significant bit
76 of the significand set. The sign of zeroes and infinities is
77 significant; the exponent and significand of such numbers is not
78 stored, but has a known implicit (deterministic) value: 0 for the
79 significands, 0 for zero exponent, all 1 bits for infinity
80 exponent. For NaNs the sign and significand are deterministic,
81 although not really meaningful, and preserved in non-conversion
82 operations. The exponent is implicitly all 1 bits.
87 Some features that may or may not be worth adding:
89 Binary to decimal conversion (hard).
91 Optional ability to detect underflow tininess before rounding.
93 New formats: x87 in single and double precision mode (IEEE apart
94 from extended exponent range) (hard).
96 New operations: sqrt, IEEE remainder, C90 fmod, nextafter,
103 // APInt contains static functions implementing bignum arithmetic.
104 #include "llvm/ADT/APInt.h"
105 #include "llvm/CodeGen/ValueTypes.h"
109 /* Exponents are stored as signed numbers. */
110 typedef signed short exponent_t;
114 /* When bits of a floating point number are truncated, this enum is
115 used to indicate what fraction of the LSB those bits represented.
116 It essentially combines the roles of guard and sticky bits. */
117 enum lostFraction { // Example of truncated bits:
118 lfExactlyZero, // 000000
119 lfLessThanHalf, // 0xxxxx x's not all zero
120 lfExactlyHalf, // 100000
121 lfMoreThanHalf // 1xxxxx x's not all zero
127 /* We support the following floating point semantics. */
128 static const fltSemantics IEEEsingle;
129 static const fltSemantics IEEEdouble;
130 static const fltSemantics IEEEquad;
131 static const fltSemantics PPCDoubleDouble;
132 static const fltSemantics x87DoubleExtended;
133 /* And this psuedo, used to construct APFloats that cannot
134 conflict with anything real. */
135 static const fltSemantics Bogus;
137 static unsigned int semanticsPrecision(const fltSemantics &);
139 /* Floating point numbers have a four-state comparison relation. */
147 /* IEEE-754R gives five rounding modes. */
156 /* Operation status. opUnderflow or opOverflow are always returned
157 or-ed with opInexact. */
167 /* Category of internally-represented number. */
176 APFloat(const fltSemantics &, const char *);
177 APFloat(const fltSemantics &, integerPart);
178 APFloat(const fltSemantics &, fltCategory, bool negative);
179 explicit APFloat(double d);
180 explicit APFloat(float f);
181 explicit APFloat(const APInt &, bool isIEEE = false);
182 APFloat(const APFloat &);
186 opStatus add(const APFloat &, roundingMode);
187 opStatus subtract(const APFloat &, roundingMode);
188 opStatus multiply(const APFloat &, roundingMode);
189 opStatus divide(const APFloat &, roundingMode);
190 opStatus mod(const APFloat &, roundingMode);
191 opStatus fusedMultiplyAdd(const APFloat &, const APFloat &, roundingMode);
193 /* Sign operations. */
196 void copySign(const APFloat &);
199 opStatus convert(const fltSemantics &, roundingMode);
200 opStatus convertToInteger(integerPart *, unsigned int, bool,
202 opStatus convertFromSignExtendedInteger(const integerPart *, unsigned int,
204 opStatus convertFromZeroExtendedInteger(const integerPart *, unsigned int,
206 opStatus convertFromString(const char *, roundingMode);
207 APInt convertToAPInt() const;
208 double convertToDouble() const;
209 float convertToFloat() const;
211 /* The definition of equality is not straightforward for floating point,
212 so we won't use operator==. Use one of the following, or write
213 whatever it is you really mean. */
214 // bool operator==(const APFloat &) const; // DO NOT IMPLEMENT
216 /* IEEE comparison with another floating point number (NaNs
217 compare unordered, 0==-0). */
218 cmpResult compare(const APFloat &) const;
220 /* Write out a hexadecimal representation of the floating point
221 value to DST, which must be of sufficient size, in the C99 form
222 [-]0xh.hhhhp[+-]d. Return the number of characters written,
223 excluding the terminating NUL. */
224 unsigned int convertToHexString(char *dst, unsigned int hexDigits,
225 bool upperCase, roundingMode) const;
227 /* Bitwise comparison for equality (QNaNs compare equal, 0!=-0). */
228 bool bitwiseIsEqual(const APFloat &) const;
230 /* Simple queries. */
231 fltCategory getCategory() const { return category; }
232 const fltSemantics &getSemantics() const { return *semantics; }
233 bool isZero() const { return category == fcZero; }
234 bool isNonZero() const { return category != fcZero; }
235 bool isNegative() const { return sign; }
236 bool isPosZero() const { return isZero() && !isNegative(); }
237 bool isNegZero() const { return isZero() && isNegative(); }
239 APFloat& operator=(const APFloat &);
241 /* Return an arbitrary integer value usable for hashing. */
242 uint32_t getHashValue() const;
246 /* Trivial queries. */
247 integerPart *significandParts();
248 const integerPart *significandParts() const;
249 unsigned int partCount() const;
251 /* Significand operations. */
252 integerPart addSignificand(const APFloat &);
253 integerPart subtractSignificand(const APFloat &, integerPart);
254 lostFraction addOrSubtractSignificand(const APFloat &, bool subtract);
255 lostFraction multiplySignificand(const APFloat &, const APFloat *);
256 lostFraction divideSignificand(const APFloat &);
257 void incrementSignificand();
258 void initialize(const fltSemantics *);
259 void shiftSignificandLeft(unsigned int);
260 lostFraction shiftSignificandRight(unsigned int);
261 unsigned int significandLSB() const;
262 unsigned int significandMSB() const;
263 void zeroSignificand();
265 /* Arithmetic on special values. */
266 opStatus addOrSubtractSpecials(const APFloat &, bool subtract);
267 opStatus divideSpecials(const APFloat &);
268 opStatus multiplySpecials(const APFloat &);
271 opStatus normalize(roundingMode, lostFraction);
272 opStatus addOrSubtract(const APFloat &, roundingMode, bool subtract);
273 cmpResult compareAbsoluteValue(const APFloat &) const;
274 opStatus handleOverflow(roundingMode);
275 bool roundAwayFromZero(roundingMode, lostFraction, unsigned int) const;
276 opStatus convertFromUnsignedParts(const integerPart *, unsigned int,
278 opStatus convertFromHexadecimalString(const char *, roundingMode);
279 opStatus convertFromDecimalString (const char *, roundingMode);
280 char *convertNormalToHexString(char *, unsigned int, bool,
282 opStatus roundSignificandWithExponent(const integerPart *, unsigned int,
285 APInt convertFloatAPFloatToAPInt() const;
286 APInt convertDoubleAPFloatToAPInt() const;
287 APInt convertF80LongDoubleAPFloatToAPInt() const;
288 APInt convertPPCDoubleDoubleAPFloatToAPInt() const;
289 void initFromAPInt(const APInt& api, bool isIEEE = false);
290 void initFromFloatAPInt(const APInt& api);
291 void initFromDoubleAPInt(const APInt& api);
292 void initFromF80LongDoubleAPInt(const APInt& api);
293 void initFromPPCDoubleDoubleAPInt(const APInt& api);
295 void assign(const APFloat &);
296 void copySignificand(const APFloat &);
297 void freeSignificand();
299 /* What kind of semantics does this value obey? */
300 const fltSemantics *semantics;
302 /* Significand - the fraction with an explicit integer bit. Must be
303 at least one bit wider than the target precision. */
310 /* The exponent - a signed number. */
313 /* What kind of floating point number this is. */
314 /* Only 2 bits are required, but VisualStudio incorrectly sign extends
315 it. Using the extra bit keeps it from failing under VisualStudio */
316 fltCategory category: 3;
318 /* The sign bit of this number. */
319 unsigned int sign: 1;
321 /* For PPCDoubleDouble, we have a second exponent and sign (the second
322 significand is appended to the first one, although it would be wrong to
323 regard these as a single number for arithmetic purposes). These fields
324 are not meaningful for any other type. */
325 exponent_t exponent2 : 11;
326 unsigned int sign2: 1;
328 } /* namespace llvm */
330 #endif /* LLVM_FLOAT_H */