Skip to content

Revert "[libc] Make FPUtils' rounding_mode.h functions constexpr." #150312

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Closed
wants to merge 1 commit into from
Closed

Revert "[libc] Make FPUtils' rounding_mode.h functions constexpr." #150312

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
1 change: 0 additions & 1 deletion libc/src/__support/FPUtil/CMakeLists.txt
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -16,7 +16,6 @@ add_header_library(
rounding_mode.h
DEPENDS
libc.hdr.fenv_macros
libc.src.__support.CPP.type_traits
libc.src.__support.macros.attributes
libc.src.__support.macros.properties.architectures
libc.src.__support.macros.sanitizer
Expand Down
67 changes: 23 additions & 44 deletions libc/src/__support/FPUtil/rounding_mode.h
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -10,7 +10,6 @@
#define LLVM_LIBC_SRC___SUPPORT_FPUTIL_ROUNDING_MODE_H

#include "hdr/fenv_macros.h"
#include "src/__support/CPP/type_traits.h" // is_constant_evaluated
#include "src/__support/macros/attributes.h" // LIBC_INLINE
#include "src/__support/macros/config.h"

Expand All @@ -21,26 +20,18 @@ namespace fputil {
// Using the following observation:
// 1.0f + 2^-25 = 1.0f for FE_TONEAREST, FE_DOWNWARD, FE_TOWARDZERO
// = 0x1.000002f for FE_UPWARD.
LIBC_INLINE static constexpr bool fenv_is_round_up() {
if (cpp::is_constant_evaluated()) {
return false;
} else {
volatile float x = 0x1.0p-25f;
return (1.0f + x != 1.0f);
}
LIBC_INLINE bool fenv_is_round_up() {
volatile float x = 0x1.0p-25f;
return (1.0f + x != 1.0f);
}

// Quick free-standing test whether fegetround() == FE_DOWNWARD.
// Using the following observation:
// -1.0f - 2^-25 = -1.0f for FE_TONEAREST, FE_UPWARD, FE_TOWARDZERO
// = -0x1.000002f for FE_DOWNWARD.
LIBC_INLINE static constexpr bool fenv_is_round_down() {
if (cpp::is_constant_evaluated()) {
return false;
} else {
volatile float x = 0x1.0p-25f;
return (-1.0f - x != -1.0f);
}
LIBC_INLINE bool fenv_is_round_down() {
volatile float x = 0x1.0p-25f;
return (-1.0f - x != -1.0f);
}

// Quick free-standing test whether fegetround() == FE_TONEAREST.
Expand All @@ -49,14 +40,10 @@ LIBC_INLINE static constexpr bool fenv_is_round_down() {
// = 0x1.100002p0f for FE_UPWARD,
// 1.5f - 2^-24 = 1.5f for FE_TONEAREST, FE_UPWARD
// = 0x1.0ffffep-1f for FE_DOWNWARD, FE_TOWARDZERO
LIBC_INLINE static constexpr bool fenv_is_round_to_nearest() {
if (cpp::is_constant_evaluated()) {
return true;
} else {
volatile float x = 0x1.0p-24f;
float y = 1.5f + x;
return (y == 1.5f - x);
}
LIBC_INLINE bool fenv_is_round_to_nearest() {
static volatile float x = 0x1.0p-24f;
float y = x;
return (1.5f + y == 1.5f - y);
}

// Quick free-standing test whether fegetround() == FE_TOWARDZERO.
Expand All @@ -69,31 +56,23 @@ LIBC_INLINE static constexpr bool fenv_is_round_to_nearest() {
// (0x1.000002p0f + 2^-24) + (-1.0f - 2^-24) = 2^-23 for FE_TOWARDZERO
// = 2^-22 for FE_TONEAREST, FE_UPWARD
// = 0 for FE_DOWNWARD
LIBC_INLINE static constexpr bool fenv_is_round_to_zero() {
if (cpp::is_constant_evaluated()) {
return false;
} else {
volatile float x = 0x1.0p-24f;
volatile float y = 0x1.000002p0f + x;
return (y + (-1.0f - x) == 0x1.0p-23f);
}
LIBC_INLINE bool fenv_is_round_to_zero() {
static volatile float x = 0x1.0p-24f;
float y = x;
return ((0x1.000002p0f + y) + (-1.0f - y) == 0x1.0p-23f);
}

// Quick free standing get rounding mode based on the above observations.
LIBC_INLINE static constexpr int quick_get_round() {
if (cpp::is_constant_evaluated()) {
return FE_TONEAREST;
} else {
volatile float x = 0x1.0p-24f;
volatile float y = 0x1.000002p0f + x;
float z = y + (-1.0f - x);
LIBC_INLINE int quick_get_round() {
static volatile float x = 0x1.0p-24f;
float y = x;
float z = (0x1.000002p0f + y) + (-1.0f - y);

if (z == 0.0f)
return FE_DOWNWARD;
if (z == 0x1.0p-23f)
return FE_TOWARDZERO;
return (2.0f + x == 2.0f) ? FE_TONEAREST : FE_UPWARD;
}
if (z == 0.0f)
return FE_DOWNWARD;
if (z == 0x1.0p-23f)
return FE_TOWARDZERO;
return (2.0f + y == 2.0f) ? FE_TONEAREST : FE_UPWARD;
}

} // namespace fputil
Expand Down
Loading