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LibJS: Simplify positive/negative zero checks

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Because both zeroes have unique and distinct bit representations,
we can bit_cast value to u64 and check if it's one of them.
This commit is contained in:
Oleg Sikorskiy 2021-03-22 21:26:16 +03:00 • committed by Andreas Kling
parent e99dabc729
commit a1014d25de
1 changed files with 6 additions and 3 deletions
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9
Userland/Libraries/LibJS/Runtime/Value.h
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@ -27,6 +27,7 @@
#pragma once #pragma once
#include <AK/Assertions.h> #include <AK/Assertions.h>
#include <AK/BitCast.h>
#include <AK/Format.h> #include <AK/Format.h>
#include <AK/Forward.h> #include <AK/Forward.h>
#include <AK/String.h> #include <AK/String.h>
@ -38,6 +39,8 @@
static constexpr double MAX_ARRAY_LIKE_INDEX = 9007199254740991.0; static constexpr double MAX_ARRAY_LIKE_INDEX = 9007199254740991.0;
// 2 ** 32 - 1 // 2 ** 32 - 1
static constexpr double MAX_U32 = 4294967295.0; static constexpr double MAX_U32 = 4294967295.0;
// Unique bit representation of negative zero (only sign bit set)
static constexpr u64 NEGATIVE_ZERO_BITS = ((u64)1 << 63);
namespace JS { namespace JS {
@ -85,8 +88,8 @@ public:
bool is_infinity() const { return is_number() && __builtin_isinf(as_double()); } bool is_infinity() const { return is_number() && __builtin_isinf(as_double()); }
bool is_positive_infinity() const { return is_number() && __builtin_isinf_sign(as_double()) > 0; } bool is_positive_infinity() const { return is_number() && __builtin_isinf_sign(as_double()) > 0; }
bool is_negative_infinity() const { return is_number() && __builtin_isinf_sign(as_double()) < 0; } bool is_negative_infinity() const { return is_number() && __builtin_isinf_sign(as_double()) < 0; }
bool is_positive_zero() const { return is_number() && 1.0 / as_double() == INFINITY; } bool is_positive_zero() const { return is_number() && bit_cast<u64>(as_double()) == 0; }
bool is_negative_zero() const { return is_number() && 1.0 / as_double() == -INFINITY; } bool is_negative_zero() const { return is_number() && bit_cast<u64>(as_double()) == NEGATIVE_ZERO_BITS; }
bool is_integer() const { return is_finite_number() && (i32)as_double() == as_double(); } bool is_integer() const { return is_finite_number() && (i32)as_double() == as_double(); }
bool is_finite_number() const bool is_finite_number() const
{ {
@ -109,7 +112,7 @@ public:
explicit Value(double value) explicit Value(double value)
{ {
bool is_negative_zero = value == 0.0 && (1.0 / value == -INFINITY); bool is_negative_zero = bit_cast<u64>(value) == NEGATIVE_ZERO_BITS;
if (value >= NumericLimits<i32>::min() && value <= NumericLimits<i32>::max() && trunc(value) == value && !is_negative_zero) { if (value >= NumericLimits<i32>::min() && value <= NumericLimits<i32>::max() && trunc(value) == value && !is_negative_zero) {
m_type = Type::Int32; m_type = Type::Int32;
m_value.as_i32 = static_cast<i32>(value); m_value.as_i32 = static_cast<i32>(value);