Add m-esr52 at 52.6.0

1 files changed, 479 insertions, 0 deletions

diff --git a/mfbt/FloatingPoint.h b/mfbt/FloatingPoint.h
new file mode 100644
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--- /dev/null
+++ b/mfbt/FloatingPoint.h
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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/* Various predicates and operations on IEEE-754 floating point types. */
+
+#ifndef mozilla_FloatingPoint_h
+#define mozilla_FloatingPoint_h
+
+#include "mozilla/Assertions.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/Casting.h"
+#include "mozilla/MathAlgorithms.h"
+#include "mozilla/Types.h"
+
+#include <stdint.h>
+
+namespace mozilla {
+
+/*
+ * It's reasonable to ask why we have this header at all.  Don't isnan,
+ * copysign, the built-in comparison operators, and the like solve these
+ * problems?  Unfortunately, they don't.  We've found that various compilers
+ * (MSVC, MSVC when compiling with PGO, and GCC on OS X, at least) miscompile
+ * the standard methods in various situations, so we can't use them.  Some of
+ * these compilers even have problems compiling seemingly reasonable bitwise
+ * algorithms!  But with some care we've found algorithms that seem to not
+ * trigger those compiler bugs.
+ *
+ * For the aforementioned reasons, be very wary of making changes to any of
+ * these algorithms.  If you must make changes, keep a careful eye out for
+ * compiler bustage, particularly PGO-specific bustage.
+ */
+
+struct FloatTypeTraits
+{
+  typedef uint32_t Bits;
+
+  static const unsigned kExponentBias = 127;
+  static const unsigned kExponentShift = 23;
+
+  static const Bits kSignBit         = 0x80000000UL;
+  static const Bits kExponentBits    = 0x7F800000UL;
+  static const Bits kSignificandBits = 0x007FFFFFUL;
+};
+
+struct DoubleTypeTraits
+{
+  typedef uint64_t Bits;
+
+  static const unsigned kExponentBias = 1023;
+  static const unsigned kExponentShift = 52;
+
+  static const Bits kSignBit         = 0x8000000000000000ULL;
+  static const Bits kExponentBits    = 0x7ff0000000000000ULL;
+  static const Bits kSignificandBits = 0x000fffffffffffffULL;
+};
+
+template<typename T> struct SelectTrait;
+template<> struct SelectTrait<float> : public FloatTypeTraits {};
+template<> struct SelectTrait<double> : public DoubleTypeTraits {};
+
+/*
+ *  This struct contains details regarding the encoding of floating-point
+ *  numbers that can be useful for direct bit manipulation. As of now, the
+ *  template parameter has to be float or double.
+ *
+ *  The nested typedef |Bits| is the unsigned integral type with the same size
+ *  as T: uint32_t for float and uint64_t for double (static assertions
+ *  double-check these assumptions).
+ *
+ *  kExponentBias is the offset that is subtracted from the exponent when
+ *  computing the value, i.e. one plus the opposite of the mininum possible
+ *  exponent.
+ *  kExponentShift is the shift that one needs to apply to retrieve the
+ *  exponent component of the value.
+ *
+ *  kSignBit contains a bits mask. Bit-and-ing with this mask will result in
+ *  obtaining the sign bit.
+ *  kExponentBits contains the mask needed for obtaining the exponent bits and
+ *  kSignificandBits contains the mask needed for obtaining the significand
+ *  bits.
+ *
+ *  Full details of how floating point number formats are encoded are beyond
+ *  the scope of this comment. For more information, see
+ *  http://en.wikipedia.org/wiki/IEEE_floating_point
+ *  http://en.wikipedia.org/wiki/Floating_point#IEEE_754:_floating_point_in_modern_computers
+ */
+template<typename T>
+struct FloatingPoint : public SelectTrait<T>
+{
+  typedef SelectTrait<T> Base;
+  typedef typename Base::Bits Bits;
+
+  static_assert((Base::kSignBit & Base::kExponentBits) == 0,
+                "sign bit shouldn't overlap exponent bits");
+  static_assert((Base::kSignBit & Base::kSignificandBits) == 0,
+                "sign bit shouldn't overlap significand bits");
+  static_assert((Base::kExponentBits & Base::kSignificandBits) == 0,
+                "exponent bits shouldn't overlap significand bits");
+
+  static_assert((Base::kSignBit | Base::kExponentBits | Base::kSignificandBits) ==
+                ~Bits(0),
+                "all bits accounted for");
+
+  /*
+   * These implementations assume float/double are 32/64-bit single/double
+   * format number types compatible with the IEEE-754 standard.  C++ don't
+   * require this to be the case.  But we required this in implementations of
+   * these algorithms that preceded this header, so we shouldn't break anything
+   * if we keep doing so.
+   */
+  static_assert(sizeof(T) == sizeof(Bits), "Bits must be same size as T");
+};
+
+/** Determines whether a float/double is NaN. */
+template<typename T>
+static MOZ_ALWAYS_INLINE bool
+IsNaN(T aValue)
+{
+  /*
+   * A float/double is NaN if all exponent bits are 1 and the significand
+   * contains at least one non-zero bit.
+   */
+  typedef FloatingPoint<T> Traits;
+  typedef typename Traits::Bits Bits;
+  return (BitwiseCast<Bits>(aValue) & Traits::kExponentBits) == Traits::kExponentBits &&
+         (BitwiseCast<Bits>(aValue) & Traits::kSignificandBits) != 0;
+}
+
+/** Determines whether a float/double is +Infinity or -Infinity. */
+template<typename T>
+static MOZ_ALWAYS_INLINE bool
+IsInfinite(T aValue)
+{
+  /* Infinities have all exponent bits set to 1 and an all-0 significand. */
+  typedef FloatingPoint<T> Traits;
+  typedef typename Traits::Bits Bits;
+  Bits bits = BitwiseCast<Bits>(aValue);
+  return (bits & ~Traits::kSignBit) == Traits::kExponentBits;
+}
+
+/** Determines whether a float/double is not NaN or infinite. */
+template<typename T>
+static MOZ_ALWAYS_INLINE bool
+IsFinite(T aValue)
+{
+  /*
+   * NaN and Infinities are the only non-finite floats/doubles, and both have
+   * all exponent bits set to 1.
+   */
+  typedef FloatingPoint<T> Traits;
+  typedef typename Traits::Bits Bits;
+  Bits bits = BitwiseCast<Bits>(aValue);
+  return (bits & Traits::kExponentBits) != Traits::kExponentBits;
+}
+
+/**
+ * Determines whether a float/double is negative or -0.  It is an error
+ * to call this method on a float/double which is NaN.
+ */
+template<typename T>
+static MOZ_ALWAYS_INLINE bool
+IsNegative(T aValue)
+{
+  MOZ_ASSERT(!IsNaN(aValue), "NaN does not have a sign");
+
+  /* The sign bit is set if the double is negative. */
+  typedef FloatingPoint<T> Traits;
+  typedef typename Traits::Bits Bits;
+  Bits bits = BitwiseCast<Bits>(aValue);
+  return (bits & Traits::kSignBit) != 0;
+}
+
+/** Determines whether a float/double represents -0. */
+template<typename T>
+static MOZ_ALWAYS_INLINE bool
+IsNegativeZero(T aValue)
+{
+  /* Only the sign bit is set if the value is -0. */
+  typedef FloatingPoint<T> Traits;
+  typedef typename Traits::Bits Bits;
+  Bits bits = BitwiseCast<Bits>(aValue);
+  return bits == Traits::kSignBit;
+}
+
+/** Determines wether a float/double represents +0. */
+template<typename T>
+static MOZ_ALWAYS_INLINE bool
+IsPositiveZero(T aValue)
+{
+  /* All bits are zero if the value is +0. */
+  typedef FloatingPoint<T> Traits;
+  typedef typename Traits::Bits Bits;
+  Bits bits = BitwiseCast<Bits>(aValue);
+  return bits == 0;
+}
+
+/**
+ * Returns 0 if a float/double is NaN or infinite;
+ * otherwise, the float/double is returned.
+ */
+template<typename T>
+static MOZ_ALWAYS_INLINE T
+ToZeroIfNonfinite(T aValue)
+{
+  return IsFinite(aValue) ? aValue : 0;
+}
+
+/**
+ * Returns the exponent portion of the float/double.
+ *
+ * Zero is not special-cased, so ExponentComponent(0.0) is
+ * -int_fast16_t(Traits::kExponentBias).
+ */
+template<typename T>
+static MOZ_ALWAYS_INLINE int_fast16_t
+ExponentComponent(T aValue)
+{
+  /*
+   * The exponent component of a float/double is an unsigned number, biased
+   * from its actual value.  Subtract the bias to retrieve the actual exponent.
+   */
+  typedef FloatingPoint<T> Traits;
+  typedef typename Traits::Bits Bits;
+  Bits bits = BitwiseCast<Bits>(aValue);
+  return int_fast16_t((bits & Traits::kExponentBits) >> Traits::kExponentShift) -
+         int_fast16_t(Traits::kExponentBias);
+}
+
+/** Returns +Infinity. */
+template<typename T>
+static MOZ_ALWAYS_INLINE T
+PositiveInfinity()
+{
+  /*
+   * Positive infinity has all exponent bits set, sign bit set to 0, and no
+   * significand.
+   */
+  typedef FloatingPoint<T> Traits;
+  return BitwiseCast<T>(Traits::kExponentBits);
+}
+
+/** Returns -Infinity. */
+template<typename T>
+static MOZ_ALWAYS_INLINE T
+NegativeInfinity()
+{
+  /*
+   * Negative infinity has all exponent bits set, sign bit set to 1, and no
+   * significand.
+   */
+  typedef FloatingPoint<T> Traits;
+  return BitwiseCast<T>(Traits::kSignBit | Traits::kExponentBits);
+}
+
+/**
+ * Computes the bit pattern for a NaN with the specified sign bit and
+ * significand bits.
+ */
+template<typename T,
+         int SignBit,
+         typename FloatingPoint<T>::Bits Significand>
+struct SpecificNaNBits
+{
+  using Traits = FloatingPoint<T>;
+
+  static_assert(SignBit == 0 || SignBit == 1, "bad sign bit");
+  static_assert((Significand & ~Traits::kSignificandBits) == 0,
+                "significand must only have significand bits set");
+  static_assert(Significand & Traits::kSignificandBits,
+                "significand must be nonzero");
+
+  static constexpr typename Traits::Bits value =
+    (SignBit * Traits::kSignBit) | Traits::kExponentBits | Significand;
+};
+
+/**
+ * Constructs a NaN value with the specified sign bit and significand bits.
+ *
+ * There is also a variant that returns the value directly.  In most cases, the
+ * two variants should be identical.  However, in the specific case of x86
+ * chips, the behavior differs: returning floating-point values directly is done
+ * through the x87 stack, and x87 loads and stores turn signaling NaNs into
+ * quiet NaNs... silently.  Returning floating-point values via outparam,
+ * however, is done entirely within the SSE registers when SSE2 floating-point
+ * is enabled in the compiler, which has semantics-preserving behavior you would
+ * expect.
+ *
+ * If preserving the distinction between signaling NaNs and quiet NaNs is
+ * important to you, you should use the outparam version.  In all other cases,
+ * you should use the direct return version.
+ */
+template<typename T>
+static MOZ_ALWAYS_INLINE void
+SpecificNaN(int signbit, typename FloatingPoint<T>::Bits significand, T* result)
+{
+  typedef FloatingPoint<T> Traits;
+  MOZ_ASSERT(signbit == 0 || signbit == 1);
+  MOZ_ASSERT((significand & ~Traits::kSignificandBits) == 0);
+  MOZ_ASSERT(significand & Traits::kSignificandBits);
+
+  BitwiseCast<T>((signbit ? Traits::kSignBit : 0) |
+                  Traits::kExponentBits |
+                  significand,
+                  result);
+  MOZ_ASSERT(IsNaN(*result));
+}
+
+template<typename T>
+static MOZ_ALWAYS_INLINE T
+SpecificNaN(int signbit, typename FloatingPoint<T>::Bits significand)
+{
+  T t;
+  SpecificNaN(signbit, significand, &t);
+  return t;
+}
+
+/** Computes the smallest non-zero positive float/double value. */
+template<typename T>
+static MOZ_ALWAYS_INLINE T
+MinNumberValue()
+{
+  typedef FloatingPoint<T> Traits;
+  typedef typename Traits::Bits Bits;
+  return BitwiseCast<T>(Bits(1));
+}
+
+/**
+ * If aValue is equal to some int32_t value, set *aInt32 to that value and
+ * return true; otherwise return false.
+ *
+ * Note that negative zero is "equal" to zero here. To test whether a value can
+ * be losslessly converted to int32_t and back, use NumberIsInt32 instead.
+ */
+template<typename T>
+static MOZ_ALWAYS_INLINE bool
+NumberEqualsInt32(T aValue, int32_t* aInt32)
+{
+  /*
+   * XXX Casting a floating-point value that doesn't truncate to int32_t, to
+   *     int32_t, induces undefined behavior.  We should definitely fix this
+   *     (bug 744965), but as apparently it "works" in practice, it's not a
+   *     pressing concern now.
+   */
+  return aValue == (*aInt32 = int32_t(aValue));
+}
+
+/**
+ * If d can be converted to int32_t and back to an identical double value,
+ * set *aInt32 to that value and return true; otherwise return false.
+ *
+ * The difference between this and NumberEqualsInt32 is that this method returns
+ * false for negative zero.
+ */
+template<typename T>
+static MOZ_ALWAYS_INLINE bool
+NumberIsInt32(T aValue, int32_t* aInt32)
+{
+  return !IsNegativeZero(aValue) && NumberEqualsInt32(aValue, aInt32);
+}
+
+/**
+ * Computes a NaN value.  Do not use this method if you depend upon a particular
+ * NaN value being returned.
+ */
+template<typename T>
+static MOZ_ALWAYS_INLINE T
+UnspecifiedNaN()
+{
+  /*
+   * If we can use any quiet NaN, we might as well use the all-ones NaN,
+   * since it's cheap to materialize on common platforms (such as x64, where
+   * this value can be represented in a 32-bit signed immediate field, allowing
+   * it to be stored to memory in a single instruction).
+   */
+  typedef FloatingPoint<T> Traits;
+  return SpecificNaN<T>(1, Traits::kSignificandBits);
+}
+
+/**
+ * Compare two doubles for equality, *without* equating -0 to +0, and equating
+ * any NaN value to any other NaN value.  (The normal equality operators equate
+ * -0 with +0, and they equate NaN to no other value.)
+ */
+template<typename T>
+static inline bool
+NumbersAreIdentical(T aValue1, T aValue2)
+{
+  typedef FloatingPoint<T> Traits;
+  typedef typename Traits::Bits Bits;
+  if (IsNaN(aValue1)) {
+    return IsNaN(aValue2);
+  }
+  return BitwiseCast<Bits>(aValue1) == BitwiseCast<Bits>(aValue2);
+}
+
+namespace detail {
+
+template<typename T>
+struct FuzzyEqualsEpsilon;
+
+template<>
+struct FuzzyEqualsEpsilon<float>
+{
+  // A number near 1e-5 that is exactly representable in a float.
+  static float value() { return 1.0f / (1 << 17); }
+};
+
+template<>
+struct FuzzyEqualsEpsilon<double>
+{
+  // A number near 1e-12 that is exactly representable in a double.
+  static double value() { return 1.0 / (1LL << 40); }
+};
+
+} // namespace detail
+
+/**
+ * Compare two floating point values for equality, modulo rounding error. That
+ * is, the two values are considered equal if they are both not NaN and if they
+ * are less than or equal to aEpsilon apart. The default value of aEpsilon is
+ * near 1e-5.
+ *
+ * For most scenarios you will want to use FuzzyEqualsMultiplicative instead,
+ * as it is more reasonable over the entire range of floating point numbers.
+ * This additive version should only be used if you know the range of the
+ * numbers you are dealing with is bounded and stays around the same order of
+ * magnitude.
+ */
+template<typename T>
+static MOZ_ALWAYS_INLINE bool
+FuzzyEqualsAdditive(T aValue1, T aValue2,
+                    T aEpsilon = detail::FuzzyEqualsEpsilon<T>::value())
+{
+  static_assert(IsFloatingPoint<T>::value, "floating point type required");
+  return Abs(aValue1 - aValue2) <= aEpsilon;
+}
+
+/**
+ * Compare two floating point values for equality, allowing for rounding error
+ * relative to the magnitude of the values. That is, the two values are
+ * considered equal if they are both not NaN and they are less than or equal to
+ * some aEpsilon apart, where the aEpsilon is scaled by the smaller of the two
+ * argument values.
+ *
+ * In most cases you will want to use this rather than FuzzyEqualsAdditive, as
+ * this function effectively masks out differences in the bottom few bits of
+ * the floating point numbers being compared, regardless of what order of
+ * magnitude those numbers are at.
+ */
+template<typename T>
+static MOZ_ALWAYS_INLINE bool
+FuzzyEqualsMultiplicative(T aValue1, T aValue2,
+                          T aEpsilon = detail::FuzzyEqualsEpsilon<T>::value())
+{
+  static_assert(IsFloatingPoint<T>::value, "floating point type required");
+  // can't use std::min because of bug 965340
+  T smaller = Abs(aValue1) < Abs(aValue2) ? Abs(aValue1) : Abs(aValue2);
+  return Abs(aValue1 - aValue2) <= aEpsilon * smaller;
+}
+
+/**
+ * Returns true if the given value can be losslessly represented as an IEEE-754
+ * single format number, false otherwise.  All NaN values are considered
+ * representable (notwithstanding that the exact bit pattern of a double format
+ * NaN value can't be exactly represented in single format).
+ *
+ * This function isn't inlined to avoid buggy optimizations by MSVC.
+ */
+MOZ_MUST_USE
+extern MFBT_API bool
+IsFloat32Representable(double aFloat32);
+
+} /* namespace mozilla */
+
+#endif /* mozilla_FloatingPoint_h */