[libc] Added support for fixed-points in `is_signed` and `is_unsigned`. #133371

kr-2003 · 2025-03-28T05:47:00Z

Changes Done

Changed the signed checking to

struct is_signed : bool_constant<((is_fixed_point<T> || is_arithmetic_v<T>) && (T(-1) < T(0)))>

in /libc/src/__support/CPP/type_traits/is_signed.h. Added check for fixed-points.

But, got to know that this will fail for unsigned _Fract or any unsigned fixed-point because unsigned _Fract can’t represent -1 in T(-1), while unsigned int can handle it via wrapping.
That's why I explicity added is_signed check for unsigned fixed-points.
Same changes to /libc/src/__support/CPP/type_traits/is_unsigned.h.
Added tests for is_signed and is_unsigned.

llvmbot · 2025-03-28T05:47:30Z

@llvm/pr-subscribers-libc

Author: Abhinav Kumar (kr-2003)

Changes

Fixes #133365

Full diff: https://github.com/llvm/llvm-project/pull/133371.diff

3 Files Affected:

(modified) libc/src/__support/CPP/type_traits/is_signed.h (+67-2)
(modified) libc/src/__support/CPP/type_traits/is_unsigned.h (+67-2)
(modified) libc/test/src/__support/CPP/type_traits_test.cpp (+59-2)

diff --git a/libc/src/__support/CPP/type_traits/is_signed.h b/libc/src/__support/CPP/type_traits/is_signed.h
index 3f56fb38aabb0..699b017eda183 100644
--- a/libc/src/__support/CPP/type_traits/is_signed.h
+++ b/libc/src/__support/CPP/type_traits/is_signed.h
@@ -8,20 +8,85 @@
 #ifndef LLVM_LIBC_SRC___SUPPORT_CPP_TYPE_TRAITS_IS_SIGNED_H
 #define LLVM_LIBC_SRC___SUPPORT_CPP_TYPE_TRAITS_IS_SIGNED_H
 
+#include "include/llvm-libc-macros/stdfix-macros.h"
 #include "src/__support/CPP/type_traits/bool_constant.h"
 #include "src/__support/CPP/type_traits/is_arithmetic.h"
+#include "src/__support/CPP/type_traits/is_fixed_point.h"
 #include "src/__support/macros/attributes.h"
 #include "src/__support/macros/config.h"
 
 namespace LIBC_NAMESPACE_DECL {
 namespace cpp {
 
-// is_signed
+// Primary template: handles arithmetic and signed fixed-point types
 template <typename T>
-struct is_signed : bool_constant<(is_arithmetic_v<T> && (T(-1) < T(0)))> {
+struct is_signed : bool_constant<((is_fixed_point_v<T> || is_arithmetic_v<T>) && (T(-1) < T(0)))> {
   LIBC_INLINE constexpr operator bool() const { return is_signed::value; }
   LIBC_INLINE constexpr bool operator()() const { return is_signed::value; }
 };
+
+// Specializations for unsigned fixed-point types
+template <>
+struct is_signed<unsigned short fract> : bool_constant<false> {
+  LIBC_INLINE constexpr operator bool() const { return is_signed::value; }
+  LIBC_INLINE constexpr bool operator()() const { return is_signed::value; }
+};
+template <>
+struct is_signed<unsigned fract> : bool_constant<false> {
+  LIBC_INLINE constexpr operator bool() const { return is_signed::value; }
+  LIBC_INLINE constexpr bool operator()() const { return is_signed::value; }
+};
+template <>
+struct is_signed<unsigned long fract> : bool_constant<false> {
+  LIBC_INLINE constexpr operator bool() const { return is_signed::value; }
+  LIBC_INLINE constexpr bool operator()() const { return is_signed::value; }
+};
+template <>
+struct is_signed<unsigned short accum> : bool_constant<false> {
+  LIBC_INLINE constexpr operator bool() const { return is_signed::value; }
+  LIBC_INLINE constexpr bool operator()() const { return is_signed::value; }
+};
+template <>
+struct is_signed<unsigned accum> : bool_constant<false> {
+  LIBC_INLINE constexpr operator bool() const { return is_signed::value; }
+  LIBC_INLINE constexpr bool operator()() const { return is_signed::value; }
+};
+template <>
+struct is_signed<unsigned long accum> : bool_constant<false> {
+  LIBC_INLINE constexpr operator bool() const { return is_signed::value; }
+  LIBC_INLINE constexpr bool operator()() const { return is_signed::value; }
+};
+template <>
+struct is_signed<unsigned short sat fract> : bool_constant<false> {
+  LIBC_INLINE constexpr operator bool() const { return is_signed::value; }
+  LIBC_INLINE constexpr bool operator()() const { return is_signed::value; }
+};
+template <>
+struct is_signed<unsigned sat fract> : bool_constant<false> {
+  LIBC_INLINE constexpr operator bool() const { return is_signed::value; }
+  LIBC_INLINE constexpr bool operator()() const { return is_signed::value; }
+};
+template <>
+struct is_signed<unsigned long sat fract> : bool_constant<false> {
+  LIBC_INLINE constexpr operator bool() const { return is_signed::value; }
+  LIBC_INLINE constexpr bool operator()() const { return is_signed::value; }
+};
+template <>
+struct is_signed<unsigned short sat accum> : bool_constant<false> {
+  LIBC_INLINE constexpr operator bool() const { return is_signed::value; }
+  LIBC_INLINE constexpr bool operator()() const { return is_signed::value; }
+};
+template <>
+struct is_signed<unsigned sat accum> : bool_constant<false> {
+  LIBC_INLINE constexpr operator bool() const { return is_signed::value; }
+  LIBC_INLINE constexpr bool operator()() const { return is_signed::value; }
+};
+template <>
+struct is_signed<unsigned long sat accum> : bool_constant<false> {
+  LIBC_INLINE constexpr operator bool() const { return is_signed::value; }
+  LIBC_INLINE constexpr bool operator()() const { return is_signed::value; }
+};
+
 template <typename T>
 LIBC_INLINE_VAR constexpr bool is_signed_v = is_signed<T>::value;
 
diff --git a/libc/src/__support/CPP/type_traits/is_unsigned.h b/libc/src/__support/CPP/type_traits/is_unsigned.h
index eed519b1c067e..58cd3f0f598a9 100644
--- a/libc/src/__support/CPP/type_traits/is_unsigned.h
+++ b/libc/src/__support/CPP/type_traits/is_unsigned.h
@@ -8,20 +8,85 @@
 #ifndef LLVM_LIBC_SRC___SUPPORT_CPP_TYPE_TRAITS_IS_UNSIGNED_H
 #define LLVM_LIBC_SRC___SUPPORT_CPP_TYPE_TRAITS_IS_UNSIGNED_H
 
+#include "include/llvm-libc-macros/stdfix-macros.h"
 #include "src/__support/CPP/type_traits/bool_constant.h"
 #include "src/__support/CPP/type_traits/is_arithmetic.h"
+#include "src/__support/CPP/type_traits/is_fixed_point.h"
 #include "src/__support/macros/attributes.h"
 #include "src/__support/macros/config.h"
 
 namespace LIBC_NAMESPACE_DECL {
 namespace cpp {
 
-// is_unsigned
+// Primary template: handles arithmetic and signed fixed-point types
 template <typename T>
-struct is_unsigned : bool_constant<(is_arithmetic_v<T> && (T(-1) > T(0)))> {
+struct is_unsigned : bool_constant<((is_fixed_point_v<T> || is_arithmetic_v<T>) && (T(-1) > T(0)))> {
   LIBC_INLINE constexpr operator bool() const { return is_unsigned::value; }
   LIBC_INLINE constexpr bool operator()() const { return is_unsigned::value; }
 };
+
+// Specializations for unsigned fixed-point types
+template <>
+struct is_unsigned<unsigned short fract> : bool_constant<true> {
+  LIBC_INLINE constexpr operator bool() const { return is_unsigned::value; }
+  LIBC_INLINE constexpr bool operator()() const { return is_unsigned::value; }
+};
+template <>
+struct is_unsigned<unsigned fract> : bool_constant<true> {
+  LIBC_INLINE constexpr operator bool() const { return is_unsigned::value; }
+  LIBC_INLINE constexpr bool operator()() const { return is_unsigned::value; }
+};
+template <>
+struct is_unsigned<unsigned long fract> : bool_constant<true> {
+  LIBC_INLINE constexpr operator bool() const { return is_unsigned::value; }
+  LIBC_INLINE constexpr bool operator()() const { return is_unsigned::value; }
+};
+template <>
+struct is_unsigned<unsigned short accum> : bool_constant<true> {
+  LIBC_INLINE constexpr operator bool() const { return is_unsigned::value; }
+  LIBC_INLINE constexpr bool operator()() const { return is_unsigned::value; }
+};
+template <>
+struct is_unsigned<unsigned accum> : bool_constant<true> {
+  LIBC_INLINE constexpr operator bool() const { return is_unsigned::value; }
+  LIBC_INLINE constexpr bool operator()() const { return is_unsigned::value; }
+};
+template <>
+struct is_unsigned<unsigned long accum> : bool_constant<true> {
+  LIBC_INLINE constexpr operator bool() const { return is_unsigned::value; }
+  LIBC_INLINE constexpr bool operator()() const { return is_unsigned::value; }
+};
+template <>
+struct is_unsigned<unsigned short sat fract> : bool_constant<true> {
+  LIBC_INLINE constexpr operator bool() const { return is_unsigned::value; }
+  LIBC_INLINE constexpr bool operator()() const { return is_unsigned::value; }
+};
+template <>
+struct is_unsigned<unsigned sat fract> : bool_constant<true> {
+  LIBC_INLINE constexpr operator bool() const { return is_unsigned::value; }
+  LIBC_INLINE constexpr bool operator()() const { return is_unsigned::value; }
+};
+template <>
+struct is_unsigned<unsigned long sat fract> : bool_constant<true> {
+  LIBC_INLINE constexpr operator bool() const { return is_unsigned::value; }
+  LIBC_INLINE constexpr bool operator()() const { return is_unsigned::value; }
+};
+template <>
+struct is_unsigned<unsigned short sat accum> : bool_constant<true> {
+  LIBC_INLINE constexpr operator bool() const { return is_unsigned::value; }
+  LIBC_INLINE constexpr bool operator()() const { return is_unsigned::value; }
+};
+template <>
+struct is_unsigned<unsigned sat accum> : bool_constant<true> {
+  LIBC_INLINE constexpr operator bool() const { return is_unsigned::value; }
+  LIBC_INLINE constexpr bool operator()() const { return is_unsigned::value; }
+};
+template <>
+struct is_unsigned<unsigned long sat accum> : bool_constant<true> {
+  LIBC_INLINE constexpr operator bool() const { return is_unsigned::value; }
+  LIBC_INLINE constexpr bool operator()() const { return is_unsigned::value; }
+};
+
 template <typename T>
 LIBC_INLINE_VAR constexpr bool is_unsigned_v = is_unsigned<T>::value;
 
diff --git a/libc/test/src/__support/CPP/type_traits_test.cpp b/libc/test/src/__support/CPP/type_traits_test.cpp
index 4b3e48c6a6c0f..338705efa5e80 100644
--- a/libc/test/src/__support/CPP/type_traits_test.cpp
+++ b/libc/test/src/__support/CPP/type_traits_test.cpp
@@ -6,6 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 
+#include "include/llvm-libc-macros/stdfix-macros.h"
 #include "src/__support/CPP/type_traits.h"
 #include "src/__support/macros/config.h"
 #include "test/UnitTest/Test.h"
@@ -409,7 +410,35 @@ TEST(LlvmLibcTypeTraitsTest, is_object) {
 
 // TODO is_scalar
 
-// TODO is_signed
+TEST(LlvmLibcTypeTraitsTest, is_signed) {
+  EXPECT_TRUE((is_signed_v<int>));
+  EXPECT_TRUE((is_signed_v<long>));
+  EXPECT_TRUE((is_signed_v<long long>));
+  EXPECT_FALSE((is_signed_v<unsigned int>));
+  EXPECT_FALSE((is_signed_v<unsigned long>));
+  EXPECT_FALSE((is_signed_v<unsigned long long>));
+  EXPECT_TRUE((is_signed_v<float>));
+  EXPECT_TRUE((is_signed_v<double>));
+  EXPECT_TRUE((is_signed_v<long double>));
+
+  // for fixed point types
+  EXPECT_TRUE((is_signed_v<fract>));
+  EXPECT_FALSE((is_signed_v<unsigned fract>));
+  EXPECT_TRUE((is_signed_v<accum>));
+  EXPECT_FALSE((is_signed_v<unsigned accum>));
+  EXPECT_TRUE((is_signed_v<sat fract>));
+  EXPECT_FALSE((is_signed_v<unsigned sat fract>));
+  EXPECT_TRUE((is_signed_v<sat accum>));
+  EXPECT_FALSE((is_signed_v<unsigned sat accum>));
+  EXPECT_TRUE((is_signed_v<short fract>));
+  EXPECT_FALSE((is_signed_v<unsigned short fract>));
+  EXPECT_TRUE((is_signed_v<short accum>));
+  EXPECT_FALSE((is_signed_v<unsigned short accum>));
+  EXPECT_TRUE((is_signed_v<long fract>));
+  EXPECT_FALSE((is_signed_v<unsigned long fract>));
+  EXPECT_TRUE((is_signed_v<long accum>));
+  EXPECT_FALSE((is_signed_v<unsigned long accum>));
+}
 
 // TODO is_trivially_constructible
 
@@ -419,7 +448,35 @@ TEST(LlvmLibcTypeTraitsTest, is_object) {
 
 // TODO is_union
 
-// TODO is_unsigned
+TEST(LlvmLibcTypeTraitsTest, is_unsigned) {
+  EXPECT_FALSE((is_unsigned_v<int>));
+  EXPECT_FALSE((is_unsigned_v<long>));
+  EXPECT_FALSE((is_unsigned_v<long long>));
+  EXPECT_TRUE((is_unsigned_v<unsigned int>));
+  EXPECT_TRUE((is_unsigned_v<unsigned long>));
+  EXPECT_TRUE((is_unsigned_v<unsigned long long>));
+  EXPECT_FALSE((is_unsigned_v<float>));
+  EXPECT_FALSE((is_unsigned_v<double>));
+  EXPECT_FALSE((is_unsigned_v<long double>));
+
+  // for fixed point types
+  EXPECT_FALSE((is_unsigned_v<fract>));
+  EXPECT_TRUE((is_unsigned_v<unsigned fract>));
+  EXPECT_FALSE((is_unsigned_v<accum>));
+  EXPECT_TRUE((is_unsigned_v<unsigned accum>));
+  EXPECT_FALSE((is_unsigned_v<sat fract>));
+  EXPECT_TRUE((is_unsigned_v<unsigned sat fract>));
+  EXPECT_FALSE((is_unsigned_v<sat accum>));
+  EXPECT_TRUE((is_unsigned_v<unsigned sat accum>));
+  EXPECT_FALSE((is_unsigned_v<short fract>));
+  EXPECT_TRUE((is_unsigned_v<unsigned short fract>));
+  EXPECT_FALSE((is_unsigned_v<short accum>));
+  EXPECT_TRUE((is_unsigned_v<unsigned short accum>));
+  EXPECT_FALSE((is_unsigned_v<long fract>));
+  EXPECT_TRUE((is_unsigned_v<unsigned long fract>));
+  EXPECT_FALSE((is_unsigned_v<long accum>));
+  EXPECT_TRUE((is_unsigned_v<unsigned long accum>));
+}
 
 // TODO is_void

github-actions · 2025-03-28T05:50:30Z

✅ With the latest revision this PR passed the C/C++ code formatter.

lntue · 2025-03-28T11:50:47Z

libc/src/__support/CPP/type_traits/is_signed.h

 template <typename T>
-struct is_signed : bool_constant<(is_arithmetic_v<T> && (T(-1) < T(0)))> {
+struct is_signed : bool_constant<((is_fixed_point_v<T> || is_arithmetic_v<T>) &&


probably you could change it to:

(is_fixed_point_v<T> && T(-0.5) < T(0)) || (is_arithmetic_v<T> && T(-1) < T(0))

and remove all the fixed point specializations.

it won't work. even if the value is just less than 0, it will try to wrap around in unsigned type(and its not possible in fixed-points). I have tried it out.

@PiJoules is there problem with constexpr for fixed point type in clang?

What's the failure mode? Is it a compilation error or failure in one of the tests?

What's the failure mode? Is it a compilation error or failure in one of the tests?

i have explained here #133680

Replied to the issue.

tl;dr overflow for non-saturating types isn't defined, so unsigned _Fract(-1) can't be constant evaluated. If you want to check if a type is signed, I think you can do FXRep<T>::MIN() < FXRep::ZERO(). I also need to update the diagnostic since it's misleading.

lntue · 2025-03-28T18:28:09Z

libc/src/__support/CPP/type_traits/is_signed.h

 template <typename T>
 struct is_signed : bool_constant<(is_arithmetic_v<T> && (T(-1) < T(0)))> {
  LIBC_INLINE constexpr operator bool() const { return is_signed::value; }
  LIBC_INLINE constexpr bool operator()() const { return is_signed::value; }
 };


So I just tested locally, and the following seems to work without all the specializations:

struct is_signed : bool_constant< (is_fixed_point_v<T> && T(-0.5) < T(0)) || (is_arithmetic_v<T> && (T(-1) < T(0)))> { ... };

really? i think i am missing out on something, because this is what i get when i try this on my machine:

/Users/llvm-project/libc/src/__support/CPP/type_traits/is_signed.h:23:34: error: non-type template argument is not a constant expression 23 | struct is_signed : bool_constant<(is_fixed_point_v<T> && T(-0.5) < T(0)) || | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 24 | (is_arithmetic_v<T> && (T(-1) < T(0)))> { | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ /Users/llvm-project/libc/src/__support/CPP/type_traits/is_signed.h:105:46: note: in instantiation of template class '__llvm_libc_21_0_0_git::cpp::is_signed<unsigned _Fract>' requested here 105 | LIBC_INLINE_VAR constexpr bool is_signed_v = is_signed<T>::value; | ^ /Users/llvm-project/libc/test/src/__support/CPP/type_traits_test.cpp:427:17: note: in instantiation of variable template specialization '__llvm_libc_21_0_0_git::cpp::is_signed_v<unsigned _Fract>' requested here 427 | EXPECT_FALSE((is_signed_v<unsigned fract>)); /Users/llvm-project/libc/src/__support/CPP/type_traits/is_signed.h:23:60: note: value 0.0 is outside the range of representable values of type 'unsigned _Fract' 23 | struct is_signed : bool_constant<(is_fixed_point_v<T> && T(-0.5) < T(0)) ||

So it looks like static_assert with that works fine, but not with EXPECT_EQ in the tests that you added. Probably something is missing for fixed point support in constexpr context.

So it looks like static_assert with that works fine, but not with EXPECT_EQ in the tests that you added. Probably something is missing for fixed point support in constexpr context.

opened issue at #133680

PiJoules · 2025-03-28T19:10:26Z

I think we'll want the saturated version of each of these also

lntue

LGTM. Let's wait for @PiJoules comments.

PiJoules

LGTM assuming you're not blocked on that compilation issue anymore

added support of fixed-points in is_signed and is_unsigned

d967f43

llvmbot added the libc label Mar 28, 2025

kr-2003 added 5 commits March 28, 2025 11:26

minor changes

b778f8f

removed redundant headers

aac912f

minor changes

dc3a4d5

clang formatting

b835679

clang formatter

a81375a

kr-2003 changed the title ~~Added support of fixed-points in is_signed and is_unsigned.~~ Added support for fixed-points in is_signed and is_unsigned. Mar 28, 2025

kr-2003 changed the title ~~Added support for fixed-points in is_signed and is_unsigned.~~ [libv] Added support for fixed-points in is_signed and is_unsigned. Mar 28, 2025

kr-2003 changed the title ~~[libv] Added support for fixed-points in is_signed and is_unsigned.~~ [libc] Added support for fixed-points in is_signed and is_unsigned. Mar 28, 2025

lntue reviewed Mar 28, 2025

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kr-2003 added 2 commits March 28, 2025 21:18

added all fixed-points explicitly

ce28db0

added all fixed-points explicitly

5d0229b

lntue reviewed Mar 28, 2025

View reviewed changes

PiJoules self-requested a review March 28, 2025 19:10

changed the design pattern

b448b38

lntue approved these changes Mar 31, 2025

View reviewed changes

PiJoules approved these changes Apr 2, 2025

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lntue merged commit 51d1c72 into llvm:main Apr 2, 2025
16 checks passed

[libc] Added support for fixed-points in is_signed and is_unsigned. #133371

[libc] Added support for fixed-points in is_signed and is_unsigned. #133371

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[libc] Added support for fixed-points in `is_signed` and `is_unsigned`. #133371

[libc] Added support for fixed-points in `is_signed` and `is_unsigned`. #133371

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