[libc-commits] [libc] [libc][NFC] Simplify FloatProperties implementation (PR #74481)
Guillaume Chatelet via libc-commits
libc-commits at lists.llvm.org
Tue Dec 5 07:01:21 PST 2023
https://github.com/gchatelet created https://github.com/llvm/llvm-project/pull/74481
This is a first patch of a series to simplify FloatProperties and FPBits
implementations.
>From 36f717f6818bc372b4bdac9875606ec74c8b7d43 Mon Sep 17 00:00:00 2001
From: Guillaume Chatelet <gchatelet at google.com>
Date: Tue, 5 Dec 2023 14:59:52 +0000
Subject: [PATCH] [libc][NFC] Simplify FloatProperties implementation
---
libc/src/__support/FPUtil/FloatProperties.h | 131 ++++++++++++++------
1 file changed, 94 insertions(+), 37 deletions(-)
diff --git a/libc/src/__support/FPUtil/FloatProperties.h b/libc/src/__support/FPUtil/FloatProperties.h
index 59e261e1047f1..7f59679c477b9 100644
--- a/libc/src/__support/FPUtil/FloatProperties.h
+++ b/libc/src/__support/FPUtil/FloatProperties.h
@@ -10,7 +10,7 @@
#define LLVM_LIBC_SRC___SUPPORT_FPUTIL_FLOATPROPERTIES_H
#include "src/__support/UInt128.h"
-#include "src/__support/macros/attributes.h" // LIBC_INLINE
+#include "src/__support/macros/attributes.h" // LIBC_INLINE, LIBC_INLINE_VAR
#include "src/__support/macros/properties/float.h" // LIBC_COMPILER_HAS_FLOAT128
#include <stdint.h>
@@ -27,22 +27,98 @@ enum class FPType {
X86_Binary80,
};
-template <FPType> struct FPProperties {};
-template <> struct FPProperties<FPType::IEEE754_Binary32> {
- typedef uint32_t BitsType;
+// For now 'FPEncoding', 'FPBaseProperties' and 'FPCommonProperties' are
+// implementation details.
+namespace internal {
+
+// The type of encoding for supported floating point types.
+enum class FPEncoding {
+ IEEE754,
+ X86_ExtendedPrecision,
+};
+
+template <FPType> struct FPBaseProperties {};
+
+template <> struct FPBaseProperties<FPType::IEEE754_Binary16> {
+ LIBC_INLINE_VAR static constexpr int FP_BITS = 16;
+ LIBC_INLINE_VAR static constexpr int SIG_BITS = 10;
+ LIBC_INLINE_VAR static constexpr int EXP_BITS = 5;
+ LIBC_INLINE_VAR static constexpr auto ENCODING = FPEncoding::IEEE754;
+ using UIntType = uint16_t;
+};
+
+template <> struct FPBaseProperties<FPType::IEEE754_Binary32> {
+ LIBC_INLINE_VAR static constexpr int FP_BITS = 32;
+ LIBC_INLINE_VAR static constexpr int SIG_BITS = 23;
+ LIBC_INLINE_VAR static constexpr int EXP_BITS = 8;
+ LIBC_INLINE_VAR static constexpr auto ENCODING = FPEncoding::IEEE754;
+ using UIntType = uint32_t;
+};
+
+template <> struct FPBaseProperties<FPType::IEEE754_Binary64> {
+ LIBC_INLINE_VAR static constexpr int FP_BITS = 64;
+ LIBC_INLINE_VAR static constexpr int SIG_BITS = 52;
+ LIBC_INLINE_VAR static constexpr int EXP_BITS = 11;
+ LIBC_INLINE_VAR static constexpr auto ENCODING = FPEncoding::IEEE754;
+ using UIntType = uint64_t;
+};
+
+template <> struct FPBaseProperties<FPType::IEEE754_Binary128> {
+ LIBC_INLINE_VAR static constexpr int FP_BITS = 128;
+ LIBC_INLINE_VAR static constexpr int SIG_BITS = 112;
+ LIBC_INLINE_VAR static constexpr int EXP_BITS = 15;
+ LIBC_INLINE_VAR static constexpr auto ENCODING = FPEncoding::IEEE754;
+ using UIntType = UInt128;
+};
+
+template <> struct FPBaseProperties<FPType::X86_Binary80> {
+ LIBC_INLINE_VAR static constexpr int FP_BITS = 80;
+ LIBC_INLINE_VAR static constexpr int SIG_BITS = 64;
+ LIBC_INLINE_VAR static constexpr int EXP_BITS = 15;
+ LIBC_INLINE_VAR static constexpr auto ENCODING =
+ FPEncoding::X86_ExtendedPrecision;
+ using UIntType = UInt128;
+};
+
+// 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> {
+ using UP = FPBaseProperties<fp_type>;
+ using BitsType = typename UP::UIntType;
+
+ LIBC_INLINE_VAR static constexpr uint32_t BIT_WIDTH = UP::FP_BITS;
+ LIBC_INLINE_VAR static constexpr uint32_t MANTISSA_WIDTH = UP::SIG_BITS;
+ LIBC_INLINE_VAR static constexpr uint32_t EXPONENT_WIDTH = UP::EXP_BITS;
+
+ // The exponent bias. Always positive.
+ LIBC_INLINE_VAR static constexpr uint32_t EXPONENT_BIAS =
+ (1U << (UP::EXP_BITS - 1U)) - 1U;
+ static_assert(EXPONENT_BIAS > 0);
+};
+
+} // namespace internal
- static constexpr uint32_t BIT_WIDTH = sizeof(BitsType) * 8;
+template <FPType> struct FPProperties {};
- static constexpr uint32_t MANTISSA_WIDTH = 23;
+// ----------------
+// Work In Progress
+// ----------------
+// The 'FPProperties' template specializations below are being slowly replaced
+// with properties from 'FPCommonProperties' above. Once specializations are
+// empty, 'FPProperties' declaration can be fully replace with
+// 'FPCommonProperties' implementation.
+
+template <>
+struct FPProperties<FPType::IEEE754_Binary32>
+ : public internal::FPCommonProperties<FPType::IEEE754_Binary32> {
// The mantissa precision includes the implicit bit.
static constexpr uint32_t MANTISSA_PRECISION = MANTISSA_WIDTH + 1;
- static constexpr uint32_t EXPONENT_WIDTH = 8;
static constexpr BitsType MANTISSA_MASK = (BitsType(1) << MANTISSA_WIDTH) - 1;
static constexpr BitsType SIGN_MASK = BitsType(1)
<< (EXPONENT_WIDTH + MANTISSA_WIDTH);
static constexpr BitsType EXPONENT_MASK = ~(SIGN_MASK | MANTISSA_MASK);
- static constexpr uint32_t EXPONENT_BIAS = 127;
-
static constexpr BitsType EXP_MANT_MASK = MANTISSA_MASK + EXPONENT_MASK;
static_assert(EXP_MANT_MASK == ~SIGN_MASK,
"Exponent and mantissa masks are not as expected.");
@@ -53,20 +129,14 @@ template <> struct FPProperties<FPType::IEEE754_Binary32> {
static constexpr BitsType QUIET_NAN_MASK = 0x00400000U;
};
-template <> struct FPProperties<FPType::IEEE754_Binary64> {
- typedef uint64_t BitsType;
-
- static constexpr uint32_t BIT_WIDTH = sizeof(BitsType) * 8;
-
- static constexpr uint32_t MANTISSA_WIDTH = 52;
+template <>
+struct FPProperties<FPType::IEEE754_Binary64>
+ : public internal::FPCommonProperties<FPType::IEEE754_Binary64> {
static constexpr uint32_t MANTISSA_PRECISION = MANTISSA_WIDTH + 1;
- static constexpr uint32_t EXPONENT_WIDTH = 11;
static constexpr BitsType MANTISSA_MASK = (BitsType(1) << MANTISSA_WIDTH) - 1;
static constexpr BitsType SIGN_MASK = BitsType(1)
<< (EXPONENT_WIDTH + MANTISSA_WIDTH);
static constexpr BitsType EXPONENT_MASK = ~(SIGN_MASK | MANTISSA_MASK);
- static constexpr uint32_t EXPONENT_BIAS = 1023;
-
static constexpr BitsType EXP_MANT_MASK = MANTISSA_MASK + EXPONENT_MASK;
static_assert(EXP_MANT_MASK == ~SIGN_MASK,
"Exponent and mantissa masks are not as expected.");
@@ -79,27 +149,20 @@ template <> struct FPProperties<FPType::IEEE754_Binary64> {
// Properties for numbers represented in 80 bits long double on non-Windows x86
// platforms.
-template <> struct FPProperties<FPType::X86_Binary80> {
- typedef UInt128 BitsType;
-
- static constexpr uint32_t BIT_WIDTH = (sizeof(BitsType) * 8) - 48;
+template <>
+struct FPProperties<FPType::X86_Binary80>
+ : public internal::FPCommonProperties<FPType::X86_Binary80> {
static constexpr BitsType FULL_WIDTH_MASK = ((BitsType(1) << BIT_WIDTH) - 1);
-
static constexpr uint32_t MANTISSA_WIDTH = 63;
static constexpr uint32_t MANTISSA_PRECISION = MANTISSA_WIDTH + 1;
- static constexpr uint32_t EXPONENT_WIDTH = 15;
static constexpr BitsType MANTISSA_MASK = (BitsType(1) << MANTISSA_WIDTH) - 1;
-
// 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);
-
static constexpr BitsType SIGN_MASK =
BitsType(1) << (EXPONENT_WIDTH + MANTISSA_WIDTH + 1);
static constexpr BitsType EXPONENT_MASK =
((BitsType(1) << EXPONENT_WIDTH) - 1) << (MANTISSA_WIDTH + 1);
- static constexpr uint32_t EXPONENT_BIAS = 16383;
-
static constexpr BitsType EXP_MANT_MASK =
MANTISSA_MASK | EXPLICIT_BIT_MASK | EXPONENT_MASK;
static_assert(EXP_MANT_MASK == (~SIGN_MASK & FULL_WIDTH_MASK),
@@ -114,20 +177,14 @@ template <> struct FPProperties<FPType::X86_Binary80> {
// Properties for numbers represented in 128 bits long double on non x86
// platform.
-template <> struct FPProperties<FPType::IEEE754_Binary128> {
- typedef UInt128 BitsType;
-
- static constexpr uint32_t BIT_WIDTH = sizeof(BitsType) << 3;
-
- static constexpr uint32_t MANTISSA_WIDTH = 112;
+template <>
+struct FPProperties<FPType::IEEE754_Binary128>
+ : public internal::FPCommonProperties<FPType::IEEE754_Binary128> {
static constexpr uint32_t MANTISSA_PRECISION = MANTISSA_WIDTH + 1;
- static constexpr uint32_t EXPONENT_WIDTH = 15;
static constexpr BitsType MANTISSA_MASK = (BitsType(1) << MANTISSA_WIDTH) - 1;
static constexpr BitsType SIGN_MASK = BitsType(1)
<< (EXPONENT_WIDTH + MANTISSA_WIDTH);
static constexpr BitsType EXPONENT_MASK = ~(SIGN_MASK | MANTISSA_MASK);
- static constexpr uint32_t EXPONENT_BIAS = 16383;
-
static constexpr BitsType EXP_MANT_MASK = MANTISSA_MASK | EXPONENT_MASK;
static_assert(EXP_MANT_MASK == ~SIGN_MASK,
"Exponent and mantissa masks are not as expected.");
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