src/__support/FPUtil/NormalFloat.h - llvm-project/libc - Git at Google

 //===-- A class to store a normalized floating point number -----*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//

 #ifndef LLVM_LIBC_SRC___SUPPORT_FPUTIL_NORMALFLOAT_H
 #define LLVM_LIBC_SRC___SUPPORT_FPUTIL_NORMALFLOAT_H

 #include "FPBits.h"

 #include "src/__support/CPP/type_traits.h"
 #include "src/__support/common.h"

 #include <stdint.h>

 namespace LIBC_NAMESPACE {
 namespace fputil {

 // A class which stores the normalized form of a floating point value.
 // The special IEEE-754 bits patterns of Zero, infinity and NaNs are
 // are not handled by this class.
 //
 // A normalized floating point number is of this form:
 //    (-1)*sign * 2^exponent * <mantissa>
 // where <mantissa> is of the form 1.<...>.
 template <typename T> struct NormalFloat {
   static_assert(
       cpp::is_floating_point_v<T>,
       "NormalFloat template parameter has to be a floating point type.");

   using StorageType = typename FPBits<T>::StorageType;
   static constexpr StorageType ONE =
       (StorageType(1) << FPBits<T>::FRACTION_LEN);

   // Unbiased exponent value.
   int32_t exponent;

   StorageType mantissa;
   // We want |StorageType| to have atleast one bit more than the actual mantissa
   // bit width to accommodate the implicit 1 value.
   static_assert(sizeof(StorageType) * 8 >= FPBits<T>::FRACTION_LEN + 1,
                 "Bad type for mantissa in NormalFloat.");

   Sign sign = Sign::POS;

   LIBC_INLINE NormalFloat(Sign s, int32_t e, StorageType m)
       : exponent(e), mantissa(m), sign(s) {
     if (mantissa >= ONE)
       return;

     unsigned normalization_shift = evaluate_normalization_shift(mantissa);
     mantissa = mantissa << normalization_shift;
     exponent -= normalization_shift;
   }

   LIBC_INLINE explicit NormalFloat(T x) { init_from_bits(FPBits<T>(x)); }

   LIBC_INLINE explicit NormalFloat(FPBits<T> bits) { init_from_bits(bits); }

   // Compares this normalized number with another normalized number.
   // Returns -1 is this number is less than |other|, 0 if this number is equal
   // to |other|, and 1 if this number is greater than |other|.
   LIBC_INLINE int cmp(const NormalFloat<T> &other) const {
     const int result = sign.is_neg() ? -1 : 1;
     if (sign != other.sign)
       return result;

     if (exponent > other.exponent) {
       return result;
     } else if (exponent == other.exponent) {
       if (mantissa > other.mantissa)
         return result;
       else if (mantissa == other.mantissa)
         return 0;
       else
         return -result;
     } else {
       return -result;
     }
   }

   // Returns a new normalized floating point number which is equal in value
   // to this number multiplied by 2^e. That is:
   //     new = this *  2^e
   LIBC_INLINE NormalFloat<T> mul2(int e) const {
     NormalFloat<T> result = *this;
     result.exponent += e;
     return result;
   }

   LIBC_INLINE operator T() const {
     int biased_exponent = exponent + FPBits<T>::EXP_BIAS;
     // Max exponent is of the form 0xFF...E. That is why -2 and not -1.
     constexpr int MAX_EXPONENT_VALUE = (1 << FPBits<T>::EXP_LEN) - 2;
     if (biased_exponent > MAX_EXPONENT_VALUE) {
       return FPBits<T>::inf(sign).get_val();
     }

     FPBits<T> result(T(0.0));
     result.set_sign(sign);

     constexpr int SUBNORMAL_EXPONENT = -FPBits<T>::EXP_BIAS + 1;
     if (exponent < SUBNORMAL_EXPONENT) {
       unsigned shift = SUBNORMAL_EXPONENT - exponent;
       // Since exponent > subnormalExponent, shift is strictly greater than
       // zero.
       if (shift <= FPBits<T>::FRACTION_LEN + 1) {
         // Generate a subnormal number. Might lead to loss of precision.
         // We round to nearest and round halfway cases to even.
         const StorageType shift_out_mask = (StorageType(1) << shift) - 1;
         const StorageType shift_out_value = mantissa & shift_out_mask;
         const StorageType halfway_value = StorageType(1) << (shift - 1);
         result.set_biased_exponent(0);
         result.set_mantissa(mantissa >> shift);
         StorageType new_mantissa = result.get_mantissa();
         if (shift_out_value > halfway_value) {
           new_mantissa += 1;
         } else if (shift_out_value == halfway_value) {
           // Round to even.
           if (result.get_mantissa() & 0x1)
             new_mantissa += 1;
         }
         result.set_mantissa(new_mantissa);
         // Adding 1 to mantissa can lead to overflow. This can only happen if
         // mantissa was all ones (0b111..11). For such a case, we will carry
         // the overflow into the exponent.
         if (new_mantissa == ONE)
           result.set_biased_exponent(1);
         return result.get_val();
       } else {
         return result.get_val();
       }
     }

     result.set_biased_exponent(exponent + FPBits<T>::EXP_BIAS);
     result.set_mantissa(mantissa);
     return result.get_val();
   }

 private:
   LIBC_INLINE void init_from_bits(FPBits<T> bits) {
     sign = bits.sign();

     if (bits.is_inf_or_nan() || bits.is_zero()) {
       // Ignore special bit patterns. Implementations deal with them separately
       // anyway so this should not be a problem.
       exponent = 0;
       mantissa = 0;
       return;
     }

     // Normalize subnormal numbers.
     if (bits.is_subnormal()) {
       unsigned shift = evaluate_normalization_shift(bits.get_mantissa());
       mantissa = StorageType(bits.get_mantissa()) << shift;
       exponent = 1 - FPBits<T>::EXP_BIAS - shift;
     } else {
       exponent = bits.get_biased_exponent() - FPBits<T>::EXP_BIAS;
       mantissa = ONE | bits.get_mantissa();
     }
   }

   LIBC_INLINE unsigned evaluate_normalization_shift(StorageType m) {
     unsigned shift = 0;
     for (; (ONE & m) == 0 && (shift < FPBits<T>::FRACTION_LEN);
          m <<= 1, ++shift)
       ;
     return shift;
   }
 };

 #ifdef LIBC_TYPES_LONG_DOUBLE_IS_X86_FLOAT80
 template <>
 LIBC_INLINE void
 NormalFloat<long double>::init_from_bits(FPBits<long double> bits) {
   sign = bits.sign();

   if (bits.is_inf_or_nan() || bits.is_zero()) {
     // Ignore special bit patterns. Implementations deal with them separately
     // anyway so this should not be a problem.
     exponent = 0;
     mantissa = 0;
     return;
   }

   if (bits.is_subnormal()) {
     if (bits.get_implicit_bit() == 0) {
       // Since we ignore zero value, the mantissa in this case is non-zero.
       int normalization_shift =
           evaluate_normalization_shift(bits.get_mantissa());
       exponent = -16382 - normalization_shift;
       mantissa = (bits.get_mantissa() << normalization_shift);
     } else {
       exponent = -16382;
       mantissa = ONE | bits.get_mantissa();
     }
   } else {
     if (bits.get_implicit_bit() == 0) {
       // Invalid number so just store 0 similar to a NaN.
       exponent = 0;
       mantissa = 0;
     } else {
       exponent = bits.get_biased_exponent() - 16383;
       mantissa = ONE | bits.get_mantissa();
     }
   }
 }

 template <> LIBC_INLINE NormalFloat<long double>::operator long double() const {
   using LDBits = FPBits<long double>;
   int biased_exponent = exponent + LDBits::EXP_BIAS;
   // Max exponent is of the form 0xFF...E. That is why -2 and not -1.
   constexpr int MAX_EXPONENT_VALUE = (1 << LDBits::EXP_LEN) - 2;
   if (biased_exponent > MAX_EXPONENT_VALUE) {
     return LDBits::inf(sign).get_val();
   }

   FPBits<long double> result(0.0l);
   result.set_sign(sign);

   constexpr int SUBNORMAL_EXPONENT = -LDBits::EXP_BIAS + 1;
   if (exponent < SUBNORMAL_EXPONENT) {
     unsigned shift = SUBNORMAL_EXPONENT - exponent;
     if (shift <= LDBits::FRACTION_LEN + 1) {
       // Generate a subnormal number. Might lead to loss of precision.
       // We round to nearest and round halfway cases to even.
       const StorageType shift_out_mask = (StorageType(1) << shift) - 1;
       const StorageType shift_out_value = mantissa & shift_out_mask;
       const StorageType halfway_value = StorageType(1) << (shift - 1);
       result.set_biased_exponent(0);
       result.set_mantissa(mantissa >> shift);
       StorageType new_mantissa = result.get_mantissa();
       if (shift_out_value > halfway_value) {
         new_mantissa += 1;
       } else if (shift_out_value == halfway_value) {
         // Round to even.
         if (result.get_mantissa() & 0x1)
           new_mantissa += 1;
       }
       result.set_mantissa(new_mantissa);
       // Adding 1 to mantissa can lead to overflow. This can only happen if
       // mantissa was all ones (0b111..11). For such a case, we will carry
       // the overflow into the exponent and set the implicit bit to 1.
       if (new_mantissa == ONE) {
         result.set_biased_exponent(1);
         result.set_implicit_bit(1);
       } else {
         result.set_implicit_bit(0);
       }
       return result.get_val();
     } else {
       return result.get_val();
     }
   }

   result.set_biased_exponent(biased_exponent);
   result.set_mantissa(mantissa);
   result.set_implicit_bit(1);
   return result.get_val();
 }
 #endif // LIBC_TYPES_LONG_DOUBLE_IS_X86_FLOAT80

 } // namespace fputil
 } // namespace LIBC_NAMESPACE

 #endif // LLVM_LIBC_SRC___SUPPORT_FPUTIL_NORMALFLOAT_H
	//===-- A class to store a normalized floating point number ------ C++ --===//
	//
	// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
	// See https://llvm.org/LICENSE.txt for license information.
	// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
	//
	//===----------------------------------------------------------------------===//

	#ifndef LLVM_LIBC_SRC___SUPPORT_FPUTIL_NORMALFLOAT_H
	#define LLVM_LIBC_SRC___SUPPORT_FPUTIL_NORMALFLOAT_H

	#include "FPBits.h"

	#include "src/__support/CPP/type_traits.h"
	#include "src/__support/common.h"

	#include <stdint.h>

	namespace LIBC_NAMESPACE {
	namespace fputil {

	// A class which stores the normalized form of a floating point value.
	// The special IEEE-754 bits patterns of Zero, infinity and NaNs are
	// are not handled by this class.
	//
	// A normalized floating point number is of this form:
	// (-1)sign 2^exponent * <mantissa>
	// where <mantissa> is of the form 1.<...>.
	template <typename T> struct NormalFloat {
	static_assert(
	cpp::is_floating_point_v<T>,
	"NormalFloat template parameter has to be a floating point type.");

	using StorageType = typename FPBits<T>::StorageType;
	static constexpr StorageType ONE =
	(StorageType(1) << FPBits<T>::FRACTION_LEN);

	// Unbiased exponent value.
	int32_t exponent;

	StorageType mantissa;
	// We want \|StorageType\| to have atleast one bit more than the actual mantissa
	// bit width to accommodate the implicit 1 value.
	static_assert(sizeof(StorageType) * 8 >= FPBits<T>::FRACTION_LEN + 1,
	"Bad type for mantissa in NormalFloat.");

	Sign sign = Sign::POS;

	LIBC_INLINE NormalFloat(Sign s, int32_t e, StorageType m)
	: exponent(e), mantissa(m), sign(s) {
	if (mantissa >= ONE)
	return;

	unsigned normalization_shift = evaluate_normalization_shift(mantissa);
	mantissa = mantissa << normalization_shift;
	exponent -= normalization_shift;
	}

	LIBC_INLINE explicit NormalFloat(T x) { init_from_bits(FPBits<T>(x)); }

	LIBC_INLINE explicit NormalFloat(FPBits<T> bits) { init_from_bits(bits); }

	// Compares this normalized number with another normalized number.
	// Returns -1 is this number is less than \|other\|, 0 if this number is equal
	// to \|other\|, and 1 if this number is greater than \|other\|.
	LIBC_INLINE int cmp(const NormalFloat<T> &other) const {
	const int result = sign.is_neg() ? -1 : 1;
	if (sign != other.sign)
	return result;

	if (exponent > other.exponent) {
	return result;
	} else if (exponent == other.exponent) {
	if (mantissa > other.mantissa)
	return result;
	else if (mantissa == other.mantissa)
	return 0;
	else
	return -result;
	} else {
	return -result;
	}
	}

	// Returns a new normalized floating point number which is equal in value
	// to this number multiplied by 2^e. That is:
	// new = this * 2^e
	LIBC_INLINE NormalFloat<T> mul2(int e) const {
	NormalFloat<T> result = *this;
	result.exponent += e;
	return result;
	}

	LIBC_INLINE operator T() const {
	int biased_exponent = exponent + FPBits<T>::EXP_BIAS;
	// Max exponent is of the form 0xFF...E. That is why -2 and not -1.
	constexpr int MAX_EXPONENT_VALUE = (1 << FPBits<T>::EXP_LEN) - 2;
	if (biased_exponent > MAX_EXPONENT_VALUE) {
	return FPBits<T>::inf(sign).get_val();
	}

	FPBits<T> result(T(0.0));
	result.set_sign(sign);

	constexpr int SUBNORMAL_EXPONENT = -FPBits<T>::EXP_BIAS + 1;
	if (exponent < SUBNORMAL_EXPONENT) {
	unsigned shift = SUBNORMAL_EXPONENT - exponent;
	// Since exponent > subnormalExponent, shift is strictly greater than
	// zero.
	if (shift <= FPBits<T>::FRACTION_LEN + 1) {
	// Generate a subnormal number. Might lead to loss of precision.
	// We round to nearest and round halfway cases to even.
	const StorageType shift_out_mask = (StorageType(1) << shift) - 1;
	const StorageType shift_out_value = mantissa & shift_out_mask;
	const StorageType halfway_value = StorageType(1) << (shift - 1);
	result.set_biased_exponent(0);
	result.set_mantissa(mantissa >> shift);
	StorageType new_mantissa = result.get_mantissa();
	if (shift_out_value > halfway_value) {
	new_mantissa += 1;
	} else if (shift_out_value == halfway_value) {
	// Round to even.
	if (result.get_mantissa() & 0x1)
	new_mantissa += 1;
	}
	result.set_mantissa(new_mantissa);
	// Adding 1 to mantissa can lead to overflow. This can only happen if
	// mantissa was all ones (0b111..11). For such a case, we will carry
	// the overflow into the exponent.
	if (new_mantissa == ONE)
	result.set_biased_exponent(1);
	return result.get_val();
	} else {
	return result.get_val();
	}
	}

	result.set_biased_exponent(exponent + FPBits<T>::EXP_BIAS);
	result.set_mantissa(mantissa);
	return result.get_val();
	}

	private:
	LIBC_INLINE void init_from_bits(FPBits<T> bits) {
	sign = bits.sign();

	if (bits.is_inf_or_nan() \|\| bits.is_zero()) {
	// Ignore special bit patterns. Implementations deal with them separately
	// anyway so this should not be a problem.
	exponent = 0;
	mantissa = 0;
	return;
	}

	// Normalize subnormal numbers.
	if (bits.is_subnormal()) {
	unsigned shift = evaluate_normalization_shift(bits.get_mantissa());
	mantissa = StorageType(bits.get_mantissa()) << shift;
	exponent = 1 - FPBits<T>::EXP_BIAS - shift;
	} else {
	exponent = bits.get_biased_exponent() - FPBits<T>::EXP_BIAS;
	mantissa = ONE \| bits.get_mantissa();
	}
	}

	LIBC_INLINE unsigned evaluate_normalization_shift(StorageType m) {
	unsigned shift = 0;
	for (; (ONE & m) == 0 && (shift < FPBits<T>::FRACTION_LEN);
	m <<= 1, ++shift)
	;
	return shift;
	}
	};

	#ifdef LIBC_TYPES_LONG_DOUBLE_IS_X86_FLOAT80
	template <>
	LIBC_INLINE void
	NormalFloat<long double>::init_from_bits(FPBits<long double> bits) {
	sign = bits.sign();

	if (bits.is_inf_or_nan() \|\| bits.is_zero()) {
	// Ignore special bit patterns. Implementations deal with them separately
	// anyway so this should not be a problem.
	exponent = 0;
	mantissa = 0;
	return;
	}

	if (bits.is_subnormal()) {
	if (bits.get_implicit_bit() == 0) {
	// Since we ignore zero value, the mantissa in this case is non-zero.
	int normalization_shift =
	evaluate_normalization_shift(bits.get_mantissa());
	exponent = -16382 - normalization_shift;
	mantissa = (bits.get_mantissa() << normalization_shift);
	} else {
	exponent = -16382;
	mantissa = ONE \| bits.get_mantissa();
	}
	} else {
	if (bits.get_implicit_bit() == 0) {
	// Invalid number so just store 0 similar to a NaN.
	exponent = 0;
	mantissa = 0;
	} else {
	exponent = bits.get_biased_exponent() - 16383;
	mantissa = ONE \| bits.get_mantissa();
	}
	}
	}

	template <> LIBC_INLINE NormalFloat<long double>::operator long double() const {
	using LDBits = FPBits<long double>;
	int biased_exponent = exponent + LDBits::EXP_BIAS;
	// Max exponent is of the form 0xFF...E. That is why -2 and not -1.
	constexpr int MAX_EXPONENT_VALUE = (1 << LDBits::EXP_LEN) - 2;
	if (biased_exponent > MAX_EXPONENT_VALUE) {
	return LDBits::inf(sign).get_val();
	}

	FPBits<long double> result(0.0l);
	result.set_sign(sign);

	constexpr int SUBNORMAL_EXPONENT = -LDBits::EXP_BIAS + 1;
	if (exponent < SUBNORMAL_EXPONENT) {
	unsigned shift = SUBNORMAL_EXPONENT - exponent;
	if (shift <= LDBits::FRACTION_LEN + 1) {
	// Generate a subnormal number. Might lead to loss of precision.
	// We round to nearest and round halfway cases to even.
	const StorageType shift_out_mask = (StorageType(1) << shift) - 1;
	const StorageType shift_out_value = mantissa & shift_out_mask;
	const StorageType halfway_value = StorageType(1) << (shift - 1);
	result.set_biased_exponent(0);
	result.set_mantissa(mantissa >> shift);
	StorageType new_mantissa = result.get_mantissa();
	if (shift_out_value > halfway_value) {
	new_mantissa += 1;
	} else if (shift_out_value == halfway_value) {
	// Round to even.
	if (result.get_mantissa() & 0x1)
	new_mantissa += 1;
	}
	result.set_mantissa(new_mantissa);
	// Adding 1 to mantissa can lead to overflow. This can only happen if
	// mantissa was all ones (0b111..11). For such a case, we will carry
	// the overflow into the exponent and set the implicit bit to 1.
	if (new_mantissa == ONE) {
	result.set_biased_exponent(1);
	result.set_implicit_bit(1);
	} else {
	result.set_implicit_bit(0);
	}
	return result.get_val();
	} else {
	return result.get_val();
	}
	}

	result.set_biased_exponent(biased_exponent);
	result.set_mantissa(mantissa);
	result.set_implicit_bit(1);
	return result.get_val();
	}
	#endif // LIBC_TYPES_LONG_DOUBLE_IS_X86_FLOAT80

	} // namespace fputil
	} // namespace LIBC_NAMESPACE

	#endif // LLVM_LIBC_SRC___SUPPORT_FPUTIL_NORMALFLOAT_H