Skip to content

[libcu++] Optimize cuda::std::saturating_cast #9724

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

Open
davebayer wants to merge 1 commit into
base: main
Choose a base branch
from
Open

[libcu++] Optimize cuda::std::saturating_cast #9724

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
14 changes: 10 additions & 4 deletions libcudacxx/include/cuda/__numeric/saturating_overflow_cast.h
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -35,13 +35,19 @@ _CCCL_TEMPLATE(class _Up, class _Tp)
_CCCL_REQUIRES(::cuda::std::__cccl_is_integer_v<_Up> _CCCL_AND ::cuda::std::__cccl_is_integer_v<_Tp>)
[[nodiscard]] _CCCL_API constexpr overflow_result<_Up> saturating_overflow_cast(_Tp __x) noexcept
{
if (::cuda::std::cmp_less(__x, ::cuda::std::numeric_limits<_Up>::min()))
if constexpr (!::cuda::std::in_range<_Up>(::cuda::std::numeric_limits<_Tp>::min()))
{
return {::cuda::std::numeric_limits<_Up>::min(), true};
if (::cuda::std::cmp_less(__x, ::cuda::std::numeric_limits<_Up>::min()))
{
return {::cuda::std::numeric_limits<_Up>::min(), true};
}
}
if (::cuda::std::cmp_greater(__x, ::cuda::std::numeric_limits<_Up>::max()))
if constexpr (!::cuda::std::in_range<_Up>(::cuda::std::numeric_limits<_Tp>::max()))
{
return {::cuda::std::numeric_limits<_Up>::max(), true};
if (::cuda::std::cmp_greater(__x, ::cuda::std::numeric_limits<_Up>::max()))
{
return {::cuda::std::numeric_limits<_Up>::max(), true};
}
}
return {static_cast<_Up>(__x), false};
}
Expand Down
349 changes: 349 additions & 0 deletions libcudacxx/include/cuda/std/__numeric/saturating_cast.h
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -23,15 +23,364 @@
#include <cuda/__numeric/saturating_overflow_cast.h>
#include <cuda/std/__concepts/concept_macros.h>
#include <cuda/std/__type_traits/is_integer.h>
#include <cuda/std/__type_traits/is_signed.h>
#include <cuda/std/__type_traits/is_unsigned.h>
#include <cuda/std/cstdint>

#include <cuda/std/__cccl/prologue.h>

_CCCL_BEGIN_NAMESPACE_CUDA_STD

#if _CCCL_CUDA_COMPILATION()
_CCCL_TEMPLATE(class _Up, class _Tp)
_CCCL_REQUIRES((sizeof(_Tp) == sizeof(int8_t)))

@Jacobfaib Jacobfaib Jul 7, 2026

Copy link
Copy Markdown
Contributor

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Did you mean sizeof(_Up) here (and the other functions)? The body checks sizeof(_Tp)

@davebayer davebayer Jul 8, 2026

Copy link
Copy Markdown
Contributor Author

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Omg yes, thank you!

[[nodiscard]] _CCCL_DEVICE_API _Up __saturating_cast_impl_device(_Tp __x, int) noexcept
{
[[maybe_unused]] int __ret;

if constexpr (sizeof(_Tp) == sizeof(int8_t))
{
if constexpr (is_signed_v<_Up> && is_unsigned_v<_Tp>)
{
asm("cvt.sat.s8.u8 %0, %1;" : "=r"(__ret) : "r"(int{__x}));
return static_cast<_Up>(__ret);
}
else if constexpr (is_unsigned_v<_Up> && is_signed_v<_Tp>)
{
asm("cvt.sat.u8.s8 %0, %1;" : "=r"(__ret) : "r"(int{__x}));
return static_cast<_Up>(__ret);
}
else
{
return __x;
}
}
else if constexpr (sizeof(_Tp) == sizeof(int16_t))
{
if constexpr (is_signed_v<_Up> && is_signed_v<_Tp>)
{
asm("cvt.sat.s8.s16 %0, %1;" : "=r"(__ret) : "h"(__x));
return static_cast<_Up>(__ret);
}
else if constexpr (is_signed_v<_Up> && is_unsigned_v<_Tp>)
{
asm("cvt.sat.s8.u16 %0, %1;" : "=r"(__ret) : "h"(__x));
return static_cast<_Up>(__ret);
}
else if constexpr (is_unsigned_v<_Up> && is_signed_v<_Tp>)
{
asm("cvt.sat.u8.s16 %0, %1;" : "=r"(__ret) : "h"(__x));
return static_cast<_Up>(__ret);
}
else
{
asm("cvt.sat.u8.u16 %0, %1;" : "=r"(__ret) : "h"(__x));
return static_cast<_Up>(__ret);
}
}
else if constexpr (sizeof(_Tp) == sizeof(int32_t))
{
if constexpr (is_signed_v<_Up> && is_signed_v<_Tp>)
{
asm("cvt.sat.s8.s32 %0, %1;" : "=r"(__ret) : "r"(__x));
return static_cast<_Up>(__ret);
}
else if constexpr (is_signed_v<_Up> && is_unsigned_v<_Tp>)
{
asm("cvt.sat.s8.u32 %0, %1;" : "=r"(__ret) : "r"(__x));
return static_cast<_Up>(__ret);
}
else if constexpr (is_unsigned_v<_Up> && is_signed_v<_Tp>)
{
asm("cvt.sat.u8.s32 %0, %1;" : "=r"(__ret) : "r"(__x));
return static_cast<_Up>(__ret);
}
else
{
asm("cvt.sat.u8.u32 %0, %1;" : "=r"(__ret) : "r"(__x));
return static_cast<_Up>(__ret);
}
}
else if constexpr (sizeof(_Tp) == sizeof(int64_t))
{
if constexpr (is_signed_v<_Up> && is_signed_v<_Tp>)
{
asm("cvt.sat.s8.s64 %0, %1;" : "=r"(__ret) : "l"(__x));
return static_cast<_Up>(__ret);
}
else if constexpr (is_signed_v<_Up> && is_unsigned_v<_Tp>)
{
asm("cvt.sat.s8.u64 %0, %1;" : "=r"(__ret) : "l"(__x));
return static_cast<_Up>(__ret);
}
else if constexpr (is_unsigned_v<_Up> && is_signed_v<_Tp>)
{
asm("cvt.sat.u8.s64 %0, %1;" : "=r"(__ret) : "l"(__x));
return static_cast<_Up>(__ret);
}
else
{
asm("cvt.sat.u8.u64 %0, %1;" : "=r"(__ret) : "l"(__x));
return static_cast<_Up>(__ret);
}
}
else
{
return ::cuda::saturating_overflow_cast<_Up>(__x).value;
}
}

_CCCL_TEMPLATE(class _Up, class _Tp)
_CCCL_REQUIRES((sizeof(_Tp) == sizeof(int16_t)))
[[nodiscard]] _CCCL_DEVICE_API _Up __saturating_cast_impl_device(_Tp __x, int) noexcept
{
[[maybe_unused]] _Up __ret;

if constexpr (sizeof(_Tp) == sizeof(int8_t))
{
if constexpr (is_unsigned_v<_Up> && is_signed_v<_Tp>)
{
asm("cvt.sat.u16.s8 %0, %1;" : "=h"(__ret) : "r"(int{__x}));
return __ret;
}
else
{
return static_cast<_Up>(__x);
}
}
else if constexpr (sizeof(_Tp) == sizeof(int16_t))
{
if constexpr (is_signed_v<_Up> && is_unsigned_v<_Tp>)
{
asm("cvt.sat.s16.u16 %0, %1;" : "=h"(__ret) : "h"(__x));
return __ret;
}
else if constexpr (is_unsigned_v<_Up> && is_signed_v<_Tp>)
{
asm("cvt.sat.u16.s16 %0, %1;" : "=h"(__ret) : "h"(__x));
return __ret;
}
else
{
return __x;
}
}
else if constexpr (sizeof(_Tp) == sizeof(int32_t))
{
if constexpr (is_signed_v<_Up> && is_signed_v<_Tp>)
{
// There is a bug on Blackwell this PTX instruction giving invalid result for negative inputs. Enable this once
// nvbug 6423103 is resolved.
NV_IF_ELSE_TARGET(NV_PROVIDES_SM_100, ({ return ::cuda::saturating_overflow_cast<_Up>(__x).value; }), ({
asm("cvt.sat.s16.s32 %0, %1;" : "=h"(__ret) : "r"(__x));
return __ret;
}))
}
else if constexpr (is_signed_v<_Up> && is_unsigned_v<_Tp>)
{
asm("cvt.sat.s16.u32 %0, %1;" : "=h"(__ret) : "r"(__x));
return __ret;
}
else if constexpr (is_unsigned_v<_Up> && is_signed_v<_Tp>)
{
asm("cvt.sat.u16.s32 %0, %1;" : "=h"(__ret) : "r"(__x));
return __ret;
}
else
{
asm("cvt.sat.u16.u32 %0, %1;" : "=h"(__ret) : "r"(__x));
return __ret;
}
}
else if constexpr (sizeof(_Tp) == sizeof(int64_t))
{
if constexpr (is_signed_v<_Up> && is_signed_v<_Tp>)
{
// There is a bug on Blackwell this PTX instruction giving invalid result for negative inputs. Enable this once
// nvbug 6423103 is resolved.
NV_IF_ELSE_TARGET(NV_PROVIDES_SM_100, ({ return ::cuda::saturating_overflow_cast<_Up>(__x).value; }), ({
asm("cvt.sat.s16.s64 %0, %1;" : "=h"(__ret) : "l"(__x));
return __ret;
}))
}
else if constexpr (is_signed_v<_Up> && is_unsigned_v<_Tp>)
{
asm("cvt.sat.s16.u64 %0, %1;" : "=h"(__ret) : "l"(__x));
return __ret;
}
else if constexpr (is_unsigned_v<_Up> && is_signed_v<_Tp>)
{
asm("cvt.sat.u16.s64 %0, %1;" : "=h"(__ret) : "l"(__x));
return __ret;
}
else
{
asm("cvt.sat.u16.u64 %0, %1;" : "=h"(__ret) : "l"(__x));
return __ret;
}
}
else
{
return ::cuda::saturating_overflow_cast<_Up>(__x).value;
}
}

_CCCL_TEMPLATE(class _Up, class _Tp)
_CCCL_REQUIRES((sizeof(_Tp) == sizeof(int32_t)))
[[nodiscard]] _CCCL_DEVICE_API _Up __saturating_cast_impl_device(_Tp __x, int) noexcept
{
[[maybe_unused]] _Up __ret;

if constexpr (sizeof(_Tp) == sizeof(int8_t))
{
if constexpr (is_unsigned_v<_Up> && is_signed_v<_Tp>)
{
asm("cvt.sat.u32.s8 %0, %1;" : "=r"(__ret) : "r"(int{__x}));
return __ret;
}
else
{
return static_cast<_Up>(__x);
}
}
else if constexpr (sizeof(_Tp) == sizeof(int16_t))
{
if constexpr (is_unsigned_v<_Up> && is_signed_v<_Tp>)
{
asm("cvt.sat.u32.s16 %0, %1;" : "=r"(__ret) : "h"(__x));
return __ret;
}
else
{
return static_cast<_Up>(__x);
}
}
else if constexpr (sizeof(_Tp) == sizeof(int32_t))
{
if constexpr (is_signed_v<_Up> && is_unsigned_v<_Tp>)
{
asm("cvt.sat.s32.u32 %0, %1;" : "=r"(__ret) : "r"(__x));
return __ret;
}
else if constexpr (is_unsigned_v<_Up> && is_signed_v<_Tp>)
{
asm("cvt.sat.u32.s32 %0, %1;" : "=r"(__ret) : "r"(__x));
return __ret;
}
else
{
return __x;
}
}
else if constexpr (sizeof(_Tp) == sizeof(int64_t))
{
if constexpr (is_signed_v<_Up> && is_signed_v<_Tp>)
{
asm("cvt.sat.s32.s64 %0, %1;" : "=r"(__ret) : "l"(__x));
return __ret;
}
else if constexpr (is_signed_v<_Up> && is_unsigned_v<_Tp>)
{
asm("cvt.sat.s32.u64 %0, %1;" : "=r"(__ret) : "l"(__x));
return __ret;
}
else if constexpr (is_unsigned_v<_Up> && is_signed_v<_Tp>)
{
asm("cvt.sat.u32.s64 %0, %1;" : "=r"(__ret) : "l"(__x));
return __ret;
}
else
{
asm("cvt.sat.u32.u64 %0, %1;" : "=r"(__ret) : "l"(__x));
return __ret;
}
}
else
{
return ::cuda::saturating_overflow_cast<_Up>(__x).value;
}
}

_CCCL_TEMPLATE(class _Up, class _Tp)
_CCCL_REQUIRES((sizeof(_Tp) == sizeof(int64_t)))
[[nodiscard]] _CCCL_DEVICE_API _Up __saturating_cast_impl_device(_Tp __x, int) noexcept
{
[[maybe_unused]] _Up __ret;

if constexpr (sizeof(_Tp) == sizeof(int8_t))
{
if constexpr (is_unsigned_v<_Up> && is_signed_v<_Tp>)
{
asm("cvt.sat.u64.s8 %0, %1;" : "=l"(__ret) : "r"(int{__x}));
return __ret;
}
else
{
return static_cast<_Up>(__x);
}
}
else if constexpr (sizeof(_Tp) == sizeof(int16_t))
{
if constexpr (is_unsigned_v<_Up> && is_signed_v<_Tp>)
{
asm("cvt.sat.u64.s16 %0, %1;" : "=l"(__ret) : "h"(__x));
return __ret;
}
else
{
return static_cast<_Up>(__x);
}
}
else if constexpr (sizeof(_Tp) == sizeof(int32_t))
{
if constexpr (is_unsigned_v<_Up> && is_signed_v<_Tp>)
{
asm("cvt.sat.u64.s32 %0, %1;" : "=l"(__ret) : "r"(__x));
return __ret;
}
else
{
return static_cast<_Up>(__x);
}
}
else if constexpr (sizeof(_Tp) == sizeof(int64_t))
{
if constexpr (is_signed_v<_Up> && is_unsigned_v<_Tp>)
{
asm("cvt.sat.s64.u64 %0, %1;" : "=l"(__ret) : "l"(__x));
return __ret;
}
else if constexpr (is_unsigned_v<_Up> && is_signed_v<_Tp>)
{
asm("cvt.sat.u64.s64 %0, %1;" : "=l"(__ret) : "l"(__x));
return __ret;
}
else
{
return __x;
}
}
else
{
return ::cuda::saturating_overflow_cast<_Up>(__x).value;
}
}

template <class _Up, class _Tp>
[[nodiscard]] _CCCL_DEVICE_API _Up __saturating_cast_impl_device(_Tp __x, long) noexcept
{
return ::cuda::saturating_overflow_cast<_Up>(__x).value;
}
#endif // _CCCL_CUDA_COMPILATION()

_CCCL_TEMPLATE(class _Up, class _Tp)
_CCCL_REQUIRES(__cccl_is_integer_v<_Up> _CCCL_AND __cccl_is_integer_v<_Tp>)
[[nodiscard]] _CCCL_API constexpr _Up saturating_cast(_Tp __x) noexcept
{
_CCCL_IF_NOT_CONSTEVAL_DEFAULT
{
NV_IF_TARGET(NV_IS_DEVICE, ({ return ::cuda::std::__saturating_cast_impl_device<_Up>(__x, 0); }))
Comment thread
fbusato marked this conversation as resolved.
}
return ::cuda::saturating_overflow_cast<_Up>(__x).value;
}

Expand Down
Loading
Loading