Revert "[reland][libc][NFC] Refactor FPBits and remove LongDoubleBits specialization" #78457
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@llvm/pr-subscribers-libc Author: Guillaume Chatelet (gchatelet) ChangesReverts llvm/llvm-project#78447 Patch is 47.06 KiB, truncated to 20.00 KiB below, full version: https://github.com/llvm/llvm-project/pull/78457.diff 9 Files Affected:
diff --git a/libc/src/__support/FPUtil/FPBits.h b/libc/src/__support/FPUtil/FPBits.h
index f67e62add2e28f..93e32ba7cc9415 100644
--- a/libc/src/__support/FPUtil/FPBits.h
+++ b/libc/src/__support/FPUtil/FPBits.h
@@ -31,40 +31,6 @@ enum class FPType {
X86_Binary80,
};
-// The classes hierarchy is as follows:
-//
-// ┌───────────────────┐
-// │ FPLayout<FPType> │
-// └─────────▲─────────┘
-// │
-// ┌─────────┴─────────┐
-// │ FPRepBase<FPType> │
-// └─────────▲─────────┘
-// │
-// ┌────────────┴─────────────┐
-// │ │
-// ┌────────┴──────┐ ┌─────────────┴──────────────┐
-// │ FPRep<FPType> │ │ FPRep<FPType::X86_Binary80 │
-// └────────▲──────┘ └─────────────▲──────────────┘
-// │ │
-// └────────────┬─────────────┘
-// │
-// ┌─────┴─────┐
-// │ FPBits<T> │
-// └───────────┘
-//
-// - 'FPLayout' defines only a few constants, namely the 'StorageType' and the
-// length of the sign, the exponent and significand parts.
-// - 'FPRepBase' builds more constants on top of those from 'FPLayout' like
-// exponent bias, shifts and masks. It also defines tools to assemble or test
-// these parts.
-// - 'FPRep' defines functions to interact with the floating point
-// representation. The default implementation is the one for 'IEEE754', a
-// specialization is provided for X86 Extended Precision that has a different
-// encoding.
-// - 'FPBits' is templated on the platform floating point types. Contrary to
-// 'FPRep' that is platform agnostic 'FPBits' is architecture dependent.
-
namespace internal {
// Defines the layout (sign, exponent, significand) of a floating point type in
@@ -166,127 +132,11 @@ struct FPRepBase : public internal::FPLayout<fp_type> {
static_assert((SIG_MASK & EXP_MASK & SIGN_MASK) == 0, "masks disjoint");
static_assert((SIG_MASK | EXP_MASK | SIGN_MASK) == FP_MASK, "masks cover");
-protected:
+private:
LIBC_INLINE static constexpr StorageType bit_at(int position) {
return StorageType(1) << position;
}
- // A stongly typed integer that prevents mixing and matching integers with
- // different semantics.
- template <typename T> struct TypedInt {
- using value_type = T;
- LIBC_INLINE constexpr explicit TypedInt(T value) : value(value) {}
- LIBC_INLINE constexpr TypedInt(const TypedInt &value) = default;
-
- LIBC_INLINE constexpr explicit operator T() const { return value; }
-
- private:
- T value;
- };
-
- // Allows explicit casting to a different type.
- template <typename To, typename T>
- LIBC_INLINE static constexpr To as(TypedInt<T> typed_int) {
- return To(static_cast<T>(typed_int));
- }
-
- // An opaque type to store a floating point exponent.
- // We define special values but it is valid to create arbitrary values as long
- // as they are in the range [MIN, MAX].
- struct Exponent : public TypedInt<int32_t> {
- using UP = TypedInt<int32_t>;
- using UP::UP;
- LIBC_INLINE
- static constexpr auto MIN() { return Exponent(1 - EXP_BIAS); }
- LIBC_INLINE static constexpr auto ZERO() { return Exponent(0); }
- LIBC_INLINE static constexpr auto MAX() { return Exponent(EXP_BIAS); }
- };
-
- // An opaque type to store a floating point biased exponent.
- // We define special values but it is valid to create arbitrary values as long
- // as they are in the range [BITS_ALL_ZEROES, BITS_ALL_ONES].
- // Values greater than BITS_ALL_ONES are truncated.
- struct BiasedExponent : public TypedInt<uint32_t> {
- using UP = TypedInt<uint32_t>;
- using UP::UP;
-
- LIBC_INLINE constexpr BiasedExponent(Exponent exp)
- : UP(static_cast<int32_t>(exp) + EXP_BIAS) {}
- // The exponent value for denormal numbers.
- LIBC_INLINE static constexpr auto BITS_ALL_ZEROES() {
- return BiasedExponent(uint32_t(0));
- }
- // The exponent value for infinity.
- LIBC_INLINE static constexpr auto BITS_ALL_ONES() {
- return BiasedExponent(uint32_t(2 * EXP_BIAS + 1));
- }
- };
-
- // An opaque type to store a floating point significand.
- // We define special values but it is valid to create arbitrary values as long
- // as they are in the range [BITS_ALL_ZEROES, BITS_ALL_ONES].
- // Note that the semantics of the Significand are implementation dependent.
- // Values greater than BITS_ALL_ONES are truncated.
- struct Significand : public TypedInt<StorageType> {
- using UP = TypedInt<StorageType>;
- using UP::UP;
-
- LIBC_INLINE friend constexpr Significand operator|(const Significand a,
- const Significand b) {
- return Significand(StorageType(as<StorageType>(a) | as<StorageType>(b)));
- }
- LIBC_INLINE friend constexpr Significand operator^(const Significand a,
- const Significand b) {
- return Significand(StorageType(as<StorageType>(a) ^ as<StorageType>(b)));
- }
- LIBC_INLINE friend constexpr Significand operator>>(const Significand a,
- int shift) {
- return Significand(StorageType(as<StorageType>(a) >> shift));
- }
-
- LIBC_INLINE static constexpr auto ZERO() {
- return Significand(StorageType(0));
- }
- LIBC_INLINE static constexpr auto LSB() {
- return Significand(StorageType(1));
- }
- LIBC_INLINE static constexpr auto MSB() {
- return Significand(StorageType(bit_at(SIG_LEN - 1)));
- }
- // Aliases
- LIBC_INLINE static constexpr auto BITS_ALL_ZEROES() { return ZERO(); }
- LIBC_INLINE static constexpr auto BITS_ALL_ONES() {
- return Significand(SIG_MASK);
- }
- };
-
- LIBC_INLINE static constexpr StorageType encode(BiasedExponent exp) {
- return (as<StorageType>(exp) << SIG_LEN) & EXP_MASK;
- }
-
- LIBC_INLINE static constexpr StorageType encode(Significand value) {
- return as<StorageType>(value) & SIG_MASK;
- }
-
- LIBC_INLINE static constexpr StorageType encode(BiasedExponent exp,
- Significand sig) {
- return encode(exp) | encode(sig);
- }
-
- LIBC_INLINE static constexpr StorageType encode(bool sign, BiasedExponent exp,
- Significand sig) {
- if (sign)
- return SIGN_MASK | encode(exp, sig);
- return encode(exp, sig);
- }
-
- LIBC_INLINE constexpr StorageType exp_bits() const { return bits & EXP_MASK; }
- LIBC_INLINE constexpr StorageType sig_bits() const { return bits & SIG_MASK; }
- LIBC_INLINE constexpr StorageType exp_sig_bits() const {
- return bits & EXP_SIG_MASK;
- }
-
-private:
// Merge bits from 'a' and 'b' values according to 'mask'.
// Use 'a' bits when corresponding 'mask' bits are zeroes and 'b' bits when
// corresponding bits are ones.
@@ -305,6 +155,20 @@ struct FPRepBase : public internal::FPLayout<fp_type> {
LIBC_INLINE_VAR static constexpr StorageType FRACTION_MASK =
mask_trailing_ones<StorageType, FRACTION_LEN>();
+ // If a number x is a NAN, then it is a quiet NAN if:
+ // QUIET_NAN_MASK & bits(x) != 0
+ LIBC_INLINE_VAR static constexpr StorageType QUIET_NAN_MASK =
+ fp_type == FPType::X86_Binary80
+ ? bit_at(SIG_LEN - 1) | bit_at(SIG_LEN - 2) // 0b1100...
+ : bit_at(SIG_LEN - 1); // 0b1000...
+
+ // Mask to generate a default signaling NAN. Any NAN that is not
+ // a quiet NAN is considered a signaling NAN.
+ LIBC_INLINE_VAR static constexpr StorageType DEFAULT_SIGNALING_NAN =
+ fp_type == FPType::X86_Binary80
+ ? bit_at(SIG_LEN - 1) | bit_at(SIG_LEN - 3) // 0b1010...
+ : bit_at(SIG_LEN - 2); // 0b0100...
+
// The floating point number representation as an unsigned integer.
StorageType bits = 0;
@@ -356,9 +220,6 @@ struct FPRepBase : public internal::FPLayout<fp_type> {
}
LIBC_INLINE constexpr StorageType uintval() const { return bits & FP_MASK; }
- LIBC_INLINE constexpr void set_uintval(StorageType value) {
- bits = (value & FP_MASK);
- }
LIBC_INLINE constexpr bool is_zero() const {
return (bits & EXP_SIG_MASK) == 0;
@@ -380,214 +241,6 @@ template <FPType fp_type> struct FPRep : public FPRepBase<fp_type> {
using UP::FRACTION_LEN;
using UP::FRACTION_MASK;
using UP::MANTISSA_PRECISION;
-
-protected:
- using typename UP::BiasedExponent;
- using typename UP::Exponent;
- using typename UP::Significand;
- using UP::encode;
- using UP::exp_bits;
- using UP::exp_sig_bits;
- using UP::sig_bits;
-
-public:
- LIBC_INLINE constexpr bool is_nan() const {
- return exp_sig_bits() >
- encode(BiasedExponent::BITS_ALL_ONES(), Significand::ZERO());
- }
- LIBC_INLINE constexpr bool is_quiet_nan() const {
- return exp_sig_bits() >=
- encode(BiasedExponent::BITS_ALL_ONES(), Significand::MSB());
- }
- LIBC_INLINE constexpr bool is_signaling_nan() const {
- return is_nan() && !is_quiet_nan();
- }
- LIBC_INLINE constexpr bool is_inf() const {
- return exp_sig_bits() ==
- encode(BiasedExponent::BITS_ALL_ONES(), Significand::ZERO());
- }
- LIBC_INLINE constexpr bool is_zero() const {
- return exp_sig_bits() ==
- encode(BiasedExponent::BITS_ALL_ZEROES(), Significand::ZERO());
- }
- LIBC_INLINE constexpr bool is_finite() const {
- return exp_bits() != encode(BiasedExponent::BITS_ALL_ONES());
- }
- LIBC_INLINE
- constexpr bool is_subnormal() const {
- return exp_bits() == encode(BiasedExponent::BITS_ALL_ZEROES());
- }
- LIBC_INLINE constexpr bool is_normal() const {
- return is_finite() && !is_subnormal();
- }
-
- LIBC_INLINE static constexpr StorageType zero(bool sign = false) {
- return encode(sign, BiasedExponent::BITS_ALL_ZEROES(), Significand::ZERO());
- }
- LIBC_INLINE static constexpr StorageType one(bool sign = false) {
- return encode(sign, Exponent::ZERO(), Significand::ZERO());
- }
- LIBC_INLINE static constexpr StorageType min_subnormal(bool sign = false) {
- return encode(sign, BiasedExponent::BITS_ALL_ZEROES(), Significand::LSB());
- }
- LIBC_INLINE static constexpr StorageType max_subnormal(bool sign = false) {
- return encode(sign, BiasedExponent::BITS_ALL_ZEROES(),
- Significand::BITS_ALL_ONES());
- }
- LIBC_INLINE static constexpr StorageType min_normal(bool sign = false) {
- return encode(sign, Exponent::MIN(), Significand::ZERO());
- }
- LIBC_INLINE static constexpr StorageType max_normal(bool sign = false) {
- return encode(sign, Exponent::MAX(), Significand::BITS_ALL_ONES());
- }
- LIBC_INLINE static constexpr StorageType inf(bool sign = false) {
- return encode(sign, BiasedExponent::BITS_ALL_ONES(), Significand::ZERO());
- }
- LIBC_INLINE static constexpr StorageType build_nan(bool sign = false,
- StorageType v = 0) {
- return encode(sign, BiasedExponent::BITS_ALL_ONES(),
- (v ? Significand(v) : (Significand::MSB() >> 1)));
- }
- LIBC_INLINE static constexpr StorageType build_quiet_nan(bool sign = false,
- StorageType v = 0) {
- return encode(sign, BiasedExponent::BITS_ALL_ONES(),
- Significand::MSB() | Significand(v));
- }
-
- // The function return mantissa with the implicit bit set iff the current
- // value is a valid normal number.
- LIBC_INLINE constexpr StorageType get_explicit_mantissa() {
- if (is_subnormal())
- return sig_bits();
- return (StorageType(1) << UP::SIG_LEN) | sig_bits();
- }
-};
-
-// Specialization for the X86 Extended Precision type.
-template <>
-struct FPRep<FPType::X86_Binary80> : public FPRepBase<FPType::X86_Binary80> {
- using UP = FPRepBase<FPType::X86_Binary80>;
- using typename UP::StorageType;
- using UP::FRACTION_LEN;
- using UP::FRACTION_MASK;
- using UP::MANTISSA_PRECISION;
-
-protected:
- using typename UP::BiasedExponent;
- using typename UP::Significand;
- using UP::encode;
-
-public:
- // The x86 80 bit float represents the leading digit of the mantissa
- // explicitly. This is the mask for that bit.
- static constexpr StorageType EXPLICIT_BIT_MASK = StorageType(1)
- << FRACTION_LEN;
- // The X80 significand is made of an explicit bit and the fractional part.
- static_assert((EXPLICIT_BIT_MASK & FRACTION_MASK) == 0,
- "the explicit bit and the fractional part should not overlap");
- static_assert((EXPLICIT_BIT_MASK | FRACTION_MASK) == SIG_MASK,
- "the explicit bit and the fractional part should cover the "
- "whole significand");
-
- LIBC_INLINE constexpr bool is_nan() const {
- // Most encoding forms from the table found in
- // https://en.wikipedia.org/wiki/Extended_precision#x86_extended_precision_format
- // are interpreted as NaN.
- // More precisely :
- // - Pseudo-Infinity
- // - Pseudo Not a Number
- // - Signalling Not a Number
- // - Floating-point Indefinite
- // - Quiet Not a Number
- // - Unnormal
- // This can be reduced to the following logic:
- if (exp_bits() == encode(BiasedExponent::BITS_ALL_ONES()))
- return !is_inf();
- if (exp_bits() != encode(BiasedExponent::BITS_ALL_ZEROES()))
- return (sig_bits() & encode(Significand::MSB())) == 0;
- return false;
- }
- LIBC_INLINE constexpr bool is_quiet_nan() const {
- return exp_sig_bits() >=
- encode(BiasedExponent::BITS_ALL_ONES(),
- Significand::MSB() | (Significand::MSB() >> 1));
- }
- LIBC_INLINE constexpr bool is_signaling_nan() const {
- return is_nan() && !is_quiet_nan();
- }
- LIBC_INLINE constexpr bool is_inf() const {
- return exp_sig_bits() ==
- encode(BiasedExponent::BITS_ALL_ONES(), Significand::MSB());
- }
- LIBC_INLINE constexpr bool is_zero() const {
- return exp_sig_bits() ==
- encode(BiasedExponent::BITS_ALL_ZEROES(), Significand::ZERO());
- }
- LIBC_INLINE constexpr bool is_finite() const {
- return !is_inf() && !is_nan();
- }
- LIBC_INLINE
- constexpr bool is_subnormal() const {
- return exp_sig_bits() >
- encode(BiasedExponent::BITS_ALL_ZEROES(), Significand::ZERO());
- }
- LIBC_INLINE constexpr bool is_normal() const {
- const auto exp = exp_bits();
- if (exp == encode(BiasedExponent::BITS_ALL_ZEROES()) ||
- exp == encode(BiasedExponent::BITS_ALL_ONES()))
- return false;
- return get_implicit_bit();
- }
-
- LIBC_INLINE static constexpr StorageType zero(bool sign = false) {
- return encode(sign, BiasedExponent::BITS_ALL_ZEROES(), Significand::ZERO());
- }
- LIBC_INLINE static constexpr StorageType one(bool sign = false) {
- return encode(sign, Exponent::ZERO(), Significand::MSB());
- }
- LIBC_INLINE static constexpr StorageType min_subnormal(bool sign = false) {
- return encode(sign, BiasedExponent::BITS_ALL_ZEROES(), Significand::LSB());
- }
- LIBC_INLINE static constexpr StorageType max_subnormal(bool sign = false) {
- return encode(sign, BiasedExponent::BITS_ALL_ZEROES(),
- Significand::BITS_ALL_ONES() ^ Significand::MSB());
- }
- LIBC_INLINE static constexpr StorageType min_normal(bool sign = false) {
- return encode(sign, Exponent::MIN(), Significand::MSB());
- }
- LIBC_INLINE static constexpr StorageType max_normal(bool sign = false) {
- return encode(sign, Exponent::MAX(), Significand::BITS_ALL_ONES());
- }
- LIBC_INLINE static constexpr StorageType inf(bool sign = false) {
- return encode(sign, BiasedExponent::BITS_ALL_ONES(), Significand::MSB());
- }
- LIBC_INLINE static constexpr StorageType build_nan(bool sign = false,
- StorageType v = 0) {
- return encode(sign, BiasedExponent::BITS_ALL_ONES(),
- Significand::MSB() |
- (v ? Significand(v) : (Significand::MSB() >> 2)));
- }
- LIBC_INLINE static constexpr StorageType build_quiet_nan(bool sign = false,
- StorageType v = 0) {
- return encode(sign, BiasedExponent::BITS_ALL_ONES(),
- Significand::MSB() | (Significand::MSB() >> 1) |
- Significand(v));
- }
-
- LIBC_INLINE constexpr StorageType get_explicit_mantissa() const {
- return sig_bits();
- }
-
- // The following functions are specific to FPRep<FPType::X86_Binary80>.
- // TODO: Remove if possible.
- LIBC_INLINE constexpr bool get_implicit_bit() const {
- return static_cast<bool>(bits & EXPLICIT_BIT_MASK);
- }
-
- LIBC_INLINE constexpr void set_implicit_bit(bool implicitVal) {
- if (get_implicit_bit() != implicitVal)
- bits ^= EXPLICIT_BIT_MASK;
- }
};
} // namespace internal
@@ -623,29 +276,47 @@ template <typename T> LIBC_INLINE static constexpr FPType get_fp_type() {
static_assert(cpp::always_false<UnqualT>, "Unsupported type");
}
-// A generic class to represent floating point formats.
-// On most platforms, the 'float' type corresponds to single precision
-// floating point numbers, the 'double' type corresponds to double precision
-// floating point numers, and the 'long double' type corresponds to the quad
-// precision floating numbers. On x86 platforms however, the 'long double'
-// type maps to an x87 floating point format.
+// A generic class to represent single precision, double precision, and quad
+// precision IEEE 754 floating point formats.
+// On most platforms, the 'float' type corresponds to single precision floating
+// point numbers, the 'double' type corresponds to double precision floating
+// point numers, and the 'long double' type corresponds to the quad precision
+// floating numbers. On x86 platforms however, the 'long double' type maps to
+// an x87 floating point format. This format is an IEEE 754 extension format.
+// It is handled as an explicit specialization of this class.
template <typename T> struct FPBits : public internal::FPRep<get_fp_type<T>()> {
static_assert(cpp::is_floating_point_v<T>,
"FPBits instantiated with invalid type.");
using UP = internal::FPRep<get_fp_type<T>()>;
- using Rep = UP;
- using StorageType = typename UP::StorageType;
+private:
+ using UP::EXP_SIG_MASK;
+ using UP::QUIET_NAN_MASK;
+ using UP::SIG_LEN;
+ using UP::SIG_MASK;
+
+public:
+ using StorageType = typename UP::StorageType;
using UP::bits;
+ using UP::EXP_BIAS;
using UP::EXP_LEN;
+ using UP::EXP_MASK;
+ using UP::EXP_MASK_SHIFT;
+ using UP::FRACTION_LEN;
+ using UP::FRACTION_MASK;
+ using UP::SIGN_MASK;
+ using UP::TOTAL_LEN;
using UP::UP;
+ using UP::get_biased_exponent;
+ using UP::is_zero;
// Constants.
static constexpr int MAX_BIASED_EXPONENT = (1 << EXP_LEN) - 1;
- static constexpr StorageType MIN_NORMAL = UP::min_normal(false);
- static constexpr StorageType MAX_NORMAL = UP::max_normal(false);
- static constexpr StorageType MIN_SUBNORMAL = UP::min_subnormal(false);
- static constexpr StorageType MAX_SUBNORMAL = UP::max_subnormal(false);
+ static constexpr StorageType MIN_SUBNORMAL = StorageType(1);
+ static constexpr StorageType MAX_SUBNORMAL = FRACTION_MASK;
+ static constexpr StorageType MIN_NORMAL = (StorageType(1) << FRACTION_LEN);
+ static constexpr StorageType MAX_NORMAL =
+ (StorageType(MAX_BIASED_EXPONENT - 1) << SIG_LEN) | SIG_MASK;
// Constructors.
LIBC_INLINE constexpr FPBits() = default;
@@ -667,58 +338,88 @@ template <typename T> struct FPBits : public internal::FPRep<get_fp_type<T>()> {
LIBC_INLINE constexpr explicit operator T() const { return get_val(); }
- LIBC_INLINE constexpr bool is_inf_or_nan() const { return !UP::is_finite(); }
+ // The function return mantissa with the implicit bit set iff the current
+ // value is a valid normal number.
+ LIBC_INLINE constexpr StorageType get_explicit_mantissa() {
+ return ((get_biased_exponent() > 0 && !is_inf_or_nan())
+ ? (FRACTION_MASK + 1)
+ : 0) |
+ (FRACTION_MASK & bits);
+ }
+
+ LIBC_INLINE constexpr bool is_inf() const {
+ return (bits & EXP_SIG...
[truncated]
|
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Jan 19, 2024
… specialization" (llvm#78457) Reverts llvm#78447 This broke the gcc buildbot.
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Reverts #78447
This broke the gcc buildbot.