initial checkin of Neil's APFloat work.

llvm-svn: 41203

llvm/include/llvm/ADT/APFloat.h

@@ -0,0 +1,258 @@
+//== 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 using 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.  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.  The library reads
+    and correctly rounds hexadecimal floating point numbers as per
+    C99; syntax is required to have been validated by the caller.
+    Conversion from decimal is not currently implemented.
+
+    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.
+
+    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
+    indeterminate and meaningless.  For QNaNs the sign bit, as well as
+    the exponent and significand are indeterminate and meaningless.
+
+    TODO
+    ====
+
+    Some features that may or may not be worth adding:
+
+    Conversions to and from decimal strings (hard).
+
+    Conversions to hexadecimal string.
+
+    Read and write IEEE-format in-memory representations.
+
+    Optional ability to detect underflow tininess before rounding.
+
+    New formats: x87 in single and double precision mode (IEEE apart
+    from extended exponent range) and IBM two-double extended
+    precision (hard).
+
+    New operations: sqrt, copysign, 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 x87DoubleExtended;
+
+    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,
+      fcQNaN,
+      fcNormal,
+      fcZero
+    };
+
+    /* Constructors.  */
+    APFloat(const fltSemantics &, const char *);
+    APFloat(const fltSemantics &, integerPart);
+    APFloat(const fltSemantics &, fltCategory, bool negative);
+    APFloat(const APFloat &);
+    ~APFloat();
+
+    /* Arithmetic.  */
+    opStatus add(const APFloat &, roundingMode);
+    opStatus subtract(const APFloat &, roundingMode);
+    opStatus multiply(const APFloat &, roundingMode);
+    opStatus divide(const APFloat &, roundingMode);
+    opStatus fusedMultiplyAdd(const APFloat &, const APFloat &, roundingMode);
+    void changeSign();
+
+    /* Conversions.  */
+    opStatus convert(const fltSemantics &, roundingMode);
+    opStatus convertToInteger(integerPart *, unsigned int, bool,
+			      roundingMode) const;
+    opStatus convertFromInteger(const integerPart *, unsigned int, bool,
+				roundingMode);
+    opStatus convertFromString(const char *, roundingMode);
+
+    /* Comparison with another floating point number.  */
+    cmpResult compare(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 isNegative() const { return sign; }
+
+    APFloat& operator=(const APFloat &);
+
+  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.  */
+    opStatus normalize(roundingMode, lostFraction);
+    opStatus addOrSubtract(const APFloat &, roundingMode, bool subtract);
+    cmpResult compareAbsoluteValue(const APFloat &) const;
+    opStatus handleOverflow(roundingMode);
+    bool roundAwayFromZero(roundingMode, lostFraction);
+    opStatus convertFromUnsignedInteger(integerPart *, unsigned int,
+					roundingMode);
+    lostFraction combineLostFractions(lostFraction, lostFraction);
+    opStatus convertFromHexadecimalString(const char *, roundingMode);
+
+    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.  */
+    fltCategory category: 2;
+
+    /* The sign bit of this number.  */
+    unsigned int sign: 1;
+  };
+} /* namespace llvm */
+
+#endif /* LLVM_FLOAT_H */

llvm/include/llvm/ADT/APInt.h

@@ -19,9 +19,7 @@
 #include <cassert>
 #include <string>
 
-#define HOST_CHAR_BIT 8
-#define compileTimeAssert(cond) extern int CTAssert[(cond) ? 1 : -1]
-#define integerPartWidth (HOST_CHAR_BIT * sizeof(llvm::integerPart))
+#define COMPILE_TIME_ASSERT(cond) extern int CTAssert[(cond) ? 1 : -1]
 
 namespace llvm {
 
@@ -29,6 +27,9 @@ namespace llvm {
      bignum.  */
   typedef uint64_t integerPart;
 
+  const unsigned int host_char_bit = 8;
+  const unsigned int integerPartWidth = host_char_bit * sizeof(integerPart);
+
 //===----------------------------------------------------------------------===//
 //                              APInt Class
 //===----------------------------------------------------------------------===//

llvm/lib/Support/APInt.cpp

@@ -2018,19 +2018,39 @@ void APInt::dump() const
 
 /* Assumed by lowHalf, highHalf, partMSB and partLSB.  A fairly safe
    and unrestricting assumption.  */
-compileTimeAssert(integerPartWidth % 2 == 0);
-
-#define lowBitMask(bits) (~(integerPart) 0 >> (integerPartWidth - (bits)))
-#define lowHalf(part) ((part) & lowBitMask(integerPartWidth / 2))
-#define highHalf(part) ((part) >> (integerPartWidth / 2))
+COMPILE_TIME_ASSERT(integerPartWidth % 2 == 0);
 
 /* Some handy functions local to this file.  */
 namespace {
 
+  /* Returns the integer part with the least significant BITS set.
+     BITS cannot be zero.  */
+  inline integerPart
+  lowBitMask(unsigned int bits)
+  {
+    assert (bits != 0 && bits <= integerPartWidth);
+
+    return ~(integerPart) 0 >> (integerPartWidth - bits);
+  }
+
+  /* Returns the value of the lower nibble of PART.  */
+  inline integerPart
+  lowHalf(integerPart part)
+  {
+    return part & lowBitMask(integerPartWidth / 2);
+  }
+
+  /* Returns the value of the upper nibble of PART.  */
+  inline integerPart
+  highHalf(integerPart part)
+  {
+    return part >> (integerPartWidth / 2);
+  }
+
   /* Returns the bit number of the most significant bit of a part.  If
      the input number has no bits set -1U is returned.  */
   unsigned int
-  PartMSB(integerPart value)
+  partMSB(integerPart value)
   {
     unsigned int n, msb;
 
@@ -2157,7 +2177,7 @@ APInt::tcMSB(const integerPart *parts, unsigned int n)
       --n;
 
       if (parts[n] != 0) {
-          msb = PartMSB(parts[n]);
+          msb = partMSB(parts[n]);
 
           return msb + n * integerPartWidth;
       }
@@ -2388,11 +2408,11 @@ APInt::tcDivide(integerPart *lhs, const integerPart *rhs,
 
   assert(lhs != remainder && lhs != srhs && remainder != srhs);
 
-  shiftCount = tcMSB(rhs, parts);
-  if (shiftCount == -1U)
+  shiftCount = tcMSB(rhs, parts) + 1;
+  if (shiftCount == 0)
     return true;
 
-  shiftCount = parts * integerPartWidth - shiftCount - 1;
+  shiftCount = parts * integerPartWidth - shiftCount;
   n = shiftCount / integerPartWidth;
   mask = (integerPart) 1 << (shiftCount % integerPartWidth);