[libc][NFC] Simplify FloatProperties implementation #74821
There are no files selected for viewing
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
| Original file line number | Diff line number | Diff line change |
|---|---|---|
|
|
@@ -80,27 +80,105 @@ template <> struct FPBaseProperties<FPType::X86_Binary80> { | |
| FPEncoding::X86_ExtendedPrecision; | ||
| }; | ||
|
|
||
| // TODO: Move this utility elsewhere. | ||
| template <typename T, size_t count> static constexpr T mask_trailing_ones() { | ||
| static_assert(cpp::is_unsigned_v<T>); | ||
| constexpr unsigned t_bits = CHAR_BIT * sizeof(T); | ||
| static_assert(count <= t_bits && "Invalid bit index"); | ||
| return count == 0 ? 0 : (T(-1) >> (t_bits - count)); | ||
| } | ||
|
|
||
| // Derives more properties from 'FPBaseProperties' above. | ||
| // This class serves as a halfway point between 'FPBaseProperties' and | ||
| // 'FPProperties' below. | ||
| template <FPType fp_type> | ||
| struct FPCommonProperties : private FPBaseProperties<fp_type> { | ||
| private: | ||
| using UP = FPBaseProperties<fp_type>; | ||
| using UP::EXP_BITS; | ||
| using UP::SIG_BITS; | ||
| using UP::TOTAL_BITS; | ||
| using UIntType = typename UP::UIntType; | ||
|
|
||
| LIBC_INLINE_VAR static constexpr int STORAGE_BITS = | ||
| sizeof(UIntType) * CHAR_BIT; | ||
| static_assert(STORAGE_BITS >= TOTAL_BITS); | ||
|
|
||
| // The number of bits to represent sign. | ||
| // For documentation purpose, always 1. | ||
| LIBC_INLINE_VAR static constexpr int SIGN_BITS = 1; | ||
| static_assert(SIGN_BITS + EXP_BITS + SIG_BITS == TOTAL_BITS); | ||
|
|
||
| // The exponent bias. Always positive. | ||
| LIBC_INLINE_VAR static constexpr int32_t EXP_BIAS = | ||
| (1U << (EXP_BITS - 1U)) - 1U; | ||
| static_assert(EXP_BIAS > 0); | ||
|
|
||
| // Shifts | ||
| LIBC_INLINE_VAR static constexpr int SIG_MASK_SHIFT = 0; | ||
| LIBC_INLINE_VAR static constexpr int EXP_MASK_SHIFT = SIG_BITS; | ||
| LIBC_INLINE_VAR static constexpr int SIGN_MASK_SHIFT = SIG_BITS + EXP_BITS; | ||
|
|
||
| // Masks | ||
| LIBC_INLINE_VAR static constexpr UIntType SIG_MASK = | ||
| mask_trailing_ones<UIntType, SIG_BITS>() << SIG_MASK_SHIFT; | ||
| LIBC_INLINE_VAR static constexpr UIntType EXP_MASK = | ||
| mask_trailing_ones<UIntType, EXP_BITS>() << EXP_MASK_SHIFT; | ||
| // Trailing underscore on SIGN_MASK_ is temporary - it will be removed | ||
| // once we can replace the public part below with the private one. | ||
| LIBC_INLINE_VAR static constexpr UIntType SIGN_MASK_ = | ||
| mask_trailing_ones<UIntType, SIGN_BITS>() << SIGN_MASK_SHIFT; | ||
| LIBC_INLINE_VAR static constexpr UIntType FP_MASK = | ||
| mask_trailing_ones<UIntType, TOTAL_BITS>(); | ||
| static_assert((SIG_MASK & EXP_MASK & SIGN_MASK_) == 0, "masks disjoint"); | ||
| static_assert((SIG_MASK | EXP_MASK | SIGN_MASK_) == FP_MASK, "masks covers"); | ||
|
|
||
| LIBC_INLINE static constexpr UIntType bit_at(int position) { | ||
| return UIntType(1) << position; | ||
| } | ||
|
|
||
| LIBC_INLINE_VAR static constexpr UIntType QNAN_MASK = | ||
| UP::ENCODING == FPEncoding::X86_ExtendedPrecision | ||
| ? bit_at(SIG_BITS - 1) | bit_at(SIG_BITS - 2) // 0b1100... | ||
|
There was a problem hiding this comment. Is there a reason for not including the exponent field to There was a problem hiding this comment. I don't quite know what to do with llvm-project/libc/src/__support/FPUtil/FloatProperties.h Lines 138 to 139 in 75193b1 The current documentation says llvm-project/libc/src/__support/FPUtil/FloatProperties.h Lines 135 to 137 in 75193b1 So it seems that being a |
||
| : bit_at(SIG_BITS - 1); // 0b1000... | ||
|
|
||
| LIBC_INLINE_VAR static constexpr UIntType SNAN_MASK = | ||
| UP::ENCODING == FPEncoding::X86_ExtendedPrecision | ||
| ? bit_at(SIG_BITS - 1) | bit_at(SIG_BITS - 3) // 0b1010... | ||
| : bit_at(SIG_BITS - 2); // 0b0100... | ||
|
|
||
| // The number of bits after the decimal dot when the number if in normal form. | ||
| LIBC_INLINE_VAR static constexpr int FRACTION_BITS = | ||
| UP::ENCODING == FPEncoding::X86_ExtendedPrecision ? SIG_BITS - 1 | ||
| : SIG_BITS; | ||
|
|
||
| public: | ||
| // Public facing API to keep the change local to this file. | ||
| using BitsType = UIntType; | ||
|
|
||
| LIBC_INLINE_VAR static constexpr uint32_t BIT_WIDTH = TOTAL_BITS; | ||
| LIBC_INLINE_VAR static constexpr uint32_t MANTISSA_WIDTH = FRACTION_BITS; | ||
| LIBC_INLINE_VAR static constexpr uint32_t MANTISSA_PRECISION = | ||
| MANTISSA_WIDTH + 1; | ||
| LIBC_INLINE_VAR static constexpr BitsType MANTISSA_MASK = | ||
| mask_trailing_ones<UIntType, MANTISSA_WIDTH>(); | ||
| LIBC_INLINE_VAR static constexpr uint32_t EXPONENT_WIDTH = EXP_BITS; | ||
| LIBC_INLINE_VAR static constexpr uint32_t EXPONENT_BIAS = | ||
| static_cast<uint32_t>(EXP_BIAS); | ||
| LIBC_INLINE_VAR static constexpr BitsType SIGN_MASK = SIGN_MASK_; | ||
| LIBC_INLINE_VAR static constexpr BitsType EXPONENT_MASK = EXP_MASK; | ||
| LIBC_INLINE_VAR static constexpr BitsType EXP_MANT_MASK = EXP_MASK | SIG_MASK; | ||
|
|
||
| // If a number x is a NAN, then it is a quiet NAN if: | ||
| // QuietNaNMask & bits(x) != 0 | ||
| // Else, it is a signalling NAN. | ||
| static constexpr BitsType QUIET_NAN_MASK = QNAN_MASK; | ||
| }; | ||
|
|
||
| } // namespace internal | ||
|
|
||
| template <FPType fp_type> | ||
| struct FPProperties : public internal::FPCommonProperties<fp_type> {}; | ||
|
|
||
| // ---------------- | ||
| // Work In Progress | ||
|
|
@@ -110,90 +188,14 @@ template <FPType> struct FPProperties {}; | |
| // empty, 'FPProperties' declaration can be fully replace with | ||
| // 'FPCommonProperties' implementation. | ||
|
|
||
| // Properties for numbers represented in 80 bits long double on non-Windows x86 | ||
| // platforms. | ||
| template <> | ||
| struct FPProperties<FPType::X86_Binary80> | ||
| : public internal::FPCommonProperties<FPType::X86_Binary80> { | ||
| // The x86 80 bit float represents the leading digit of the mantissa | ||
| // explicitly. This is the mask for that bit. | ||
| static constexpr BitsType EXPLICIT_BIT_MASK = (BitsType(1) << MANTISSA_WIDTH); | ||
| }; | ||
|
|
||
| //----------------------------------------------------------------------------- | ||
|
|
||
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
Uh oh!
There was an error while loading. Please reload this page.