[libc-commits] [libc] [libc] Fixing float128 UB error (PR #211593)
via libc-commits
libc-commits at lists.llvm.org
Wed Jul 29 02:36:20 PDT 2026
https://github.com/Sukumarsawant updated https://github.com/llvm/llvm-project/pull/211593
>From accfc9c9dc8f35e78f7927c28fd880a085896cf3 Mon Sep 17 00:00:00 2001
From: Sukumarsawant <sawantsukumar at gmail.com>
Date: Thu, 23 Jul 2026 21:08:19 +0530
Subject: [PATCH 1/7] initial test commit
---
libc/test/src/__support/FPUtil/float128_test.cpp | 2 ++
1 file changed, 2 insertions(+)
diff --git a/libc/test/src/__support/FPUtil/float128_test.cpp b/libc/test/src/__support/FPUtil/float128_test.cpp
index b4ee0439ba0f5..c971b01925867 100644
--- a/libc/test/src/__support/FPUtil/float128_test.cpp
+++ b/libc/test/src/__support/FPUtil/float128_test.cpp
@@ -87,6 +87,8 @@ TEST(LlvmLibcFloat128Test, IntegerConversion) {
ASSERT_EQ(static_cast<long long>(Float128(LLONG_MIN)), LLONG_MIN);
ASSERT_EQ(static_cast<unsigned>(Float128(UINT_MAX)), UINT_MAX);
ASSERT_EQ(static_cast<unsigned>(Float128(0U)), 0U);
+ int a = static_cast<int>(Float128(1e300));
+ (void)a;
// FP exceptions
LIBC_NAMESPACE::fputil::clear_except(FE_ALL_EXCEPT);
>From 79699cd9f7fd1557f92178093b6ed64735278391 Mon Sep 17 00:00:00 2001
From: Sukumarsawant <sawantsukumar at gmail.com>
Date: Thu, 23 Jul 2026 21:23:37 +0530
Subject: [PATCH 2/7] sanitizer
---
libc/test/src/__support/FPUtil/CMakeLists.txt | 2 ++
1 file changed, 2 insertions(+)
diff --git a/libc/test/src/__support/FPUtil/CMakeLists.txt b/libc/test/src/__support/FPUtil/CMakeLists.txt
index cab95df0e709c..ee2bbf688b1cb 100644
--- a/libc/test/src/__support/FPUtil/CMakeLists.txt
+++ b/libc/test/src/__support/FPUtil/CMakeLists.txt
@@ -49,6 +49,8 @@ add_fp_unittest(
libc.hdr.limits_macros
libc.src.__support.FPUtil.fenv_impl
libc.src.__support.FPUtil.float128
+ COMPILE_OPTIONS
+ "-fsanitize=address"
)
# TODO: Temporally disable bfloat16 test until MPCommon target is updated
>From 9caa9b763dc8c40cb8cc3fa196403d61fb1db5f9 Mon Sep 17 00:00:00 2001
From: Sukumarsawant <sawantsukumar at gmail.com>
Date: Thu, 23 Jul 2026 21:27:34 +0530
Subject: [PATCH 3/7] chore:add volatile
---
libc/test/src/__support/FPUtil/float128_test.cpp | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)
diff --git a/libc/test/src/__support/FPUtil/float128_test.cpp b/libc/test/src/__support/FPUtil/float128_test.cpp
index c971b01925867..664f32f1d74c5 100644
--- a/libc/test/src/__support/FPUtil/float128_test.cpp
+++ b/libc/test/src/__support/FPUtil/float128_test.cpp
@@ -87,8 +87,7 @@ TEST(LlvmLibcFloat128Test, IntegerConversion) {
ASSERT_EQ(static_cast<long long>(Float128(LLONG_MIN)), LLONG_MIN);
ASSERT_EQ(static_cast<unsigned>(Float128(UINT_MAX)), UINT_MAX);
ASSERT_EQ(static_cast<unsigned>(Float128(0U)), 0U);
- int a = static_cast<int>(Float128(1e300));
- (void)a;
+ volatile int a = static_cast<int>(Float128(1e300));
// FP exceptions
LIBC_NAMESPACE::fputil::clear_except(FE_ALL_EXCEPT);
>From 3745d968e089d7988aca442033f22bff5a02522b Mon Sep 17 00:00:00 2001
From: Sukumarsawant <sawantsukumar at gmail.com>
Date: Wed, 29 Jul 2026 01:52:54 +0530
Subject: [PATCH 4/7] add missing numeric_limits check and modification to
handle very small and very large values
---
libc/src/__support/FPUtil/CMakeLists.txt | 1 +
libc/src/__support/FPUtil/dyadic_float.h | 4 +++-
libc/src/__support/FPUtil/float128.h | 21 +++++++++++++++++--
libc/test/src/__support/FPUtil/CMakeLists.txt | 2 --
.../src/__support/FPUtil/float128_test.cpp | 3 ++-
5 files changed, 25 insertions(+), 6 deletions(-)
diff --git a/libc/src/__support/FPUtil/CMakeLists.txt b/libc/src/__support/FPUtil/CMakeLists.txt
index 8b6ac8027b52d..ab423a2622e5f 100644
--- a/libc/src/__support/FPUtil/CMakeLists.txt
+++ b/libc/src/__support/FPUtil/CMakeLists.txt
@@ -310,6 +310,7 @@ add_header_library(
libc.src.__support.macros.attributes
libc.src.__support.macros.config
libc.src.__support.uint128
+ libc.src.__support.CPP.limits
)
add_subdirectory(generic)
diff --git a/libc/src/__support/FPUtil/dyadic_float.h b/libc/src/__support/FPUtil/dyadic_float.h
index c218632131934..d548ee2b14561 100644
--- a/libc/src/__support/FPUtil/dyadic_float.h
+++ b/libc/src/__support/FPUtil/dyadic_float.h
@@ -471,7 +471,9 @@ template <size_t Bits> struct DyadicFloat {
// to avoid undefined behavior negating INT_MIN as an integer (although
// exponents coming in to this function _shouldn't_ be that large). The
// result should always end up as a positive size_t.
- size_t shift = -static_cast<size_t>(exponent);
+ size_t shift = cpp::min(
+ -static_cast<size_t>(exponent),
+ static_cast<size_t>(cpp::numeric_limits<MantissaType>::digits));
new_mant >>= shift;
}
diff --git a/libc/src/__support/FPUtil/float128.h b/libc/src/__support/FPUtil/float128.h
index b1bcafefd61a4..e7db3594b4e9e 100644
--- a/libc/src/__support/FPUtil/float128.h
+++ b/libc/src/__support/FPUtil/float128.h
@@ -10,6 +10,7 @@
#define LLVM_LIBC_SRC___SUPPORT_FPUTIL_FLOAT128_H
#include "hdr/stdint_proxy.h"
+#include "src/__support/CPP/limits.h"
#include "src/__support/CPP/type_traits.h"
#include "src/__support/FPUtil/cast.h"
#include "src/__support/FPUtil/comparison_operations.h"
@@ -69,13 +70,29 @@ struct Float128 {
template <typename T, cpp::enable_if_t<cpp::is_integral_v<T>, int> = 0>
LIBC_INLINE constexpr explicit operator T() const {
+ constexpr T MIN_T = cpp::numeric_limits<T>::min();
+ constexpr T MAX_T = cpp::numeric_limits<T>::max();
FPBits<Float128> x_bits(*this);
// Raise FE_INVALID for inf and NaN
if (x_bits.is_inf_or_nan()) {
raise_except_if_required(FE_INVALID);
+ return x_bits.is_neg() ? MIN_T : MAX_T;
}
- int x_bits_exp =
- x_bits.get_explicit_exponent() - FPBits<Float128>::FRACTION_LEN;
+ int exponent = x_bits.get_explicit_exponent();
+ constexpr int EXPONENT_LIMIT = cpp::is_signed_v<T>
+ ? static_cast<int>(sizeof(T) * 8) - 1
+ : static_cast<int>(sizeof(T) * 8);
+ if (exponent > EXPONENT_LIMIT) {
+ raise_except_if_required(FE_INVALID);
+ return x_bits.is_neg() ? MIN_T : MAX_T;
+ } else if (exponent == EXPONENT_LIMIT) {
+ if (x_bits.is_pos() || x_bits.get_mantissa() != 0) {
+ raise_except_if_required(FE_INVALID);
+ return x_bits.is_neg() ? MIN_T : MAX_T;
+ }
+ }
+
+ int x_bits_exp = exponent - FPBits<Float128>::FRACTION_LEN;
// sign * 2^(exp-bias) * mantissa
DyadicFloat<FPBits<Float128>::STORAGE_LEN> xd(
x_bits.sign(), x_bits_exp, x_bits.get_explicit_mantissa());
diff --git a/libc/test/src/__support/FPUtil/CMakeLists.txt b/libc/test/src/__support/FPUtil/CMakeLists.txt
index ee2bbf688b1cb..cab95df0e709c 100644
--- a/libc/test/src/__support/FPUtil/CMakeLists.txt
+++ b/libc/test/src/__support/FPUtil/CMakeLists.txt
@@ -49,8 +49,6 @@ add_fp_unittest(
libc.hdr.limits_macros
libc.src.__support.FPUtil.fenv_impl
libc.src.__support.FPUtil.float128
- COMPILE_OPTIONS
- "-fsanitize=address"
)
# TODO: Temporally disable bfloat16 test until MPCommon target is updated
diff --git a/libc/test/src/__support/FPUtil/float128_test.cpp b/libc/test/src/__support/FPUtil/float128_test.cpp
index 664f32f1d74c5..4982f2a61fdc1 100644
--- a/libc/test/src/__support/FPUtil/float128_test.cpp
+++ b/libc/test/src/__support/FPUtil/float128_test.cpp
@@ -87,7 +87,8 @@ TEST(LlvmLibcFloat128Test, IntegerConversion) {
ASSERT_EQ(static_cast<long long>(Float128(LLONG_MIN)), LLONG_MIN);
ASSERT_EQ(static_cast<unsigned>(Float128(UINT_MAX)), UINT_MAX);
ASSERT_EQ(static_cast<unsigned>(Float128(0U)), 0U);
- volatile int a = static_cast<int>(Float128(1e300));
+ volatile int a = static_cast<int>(Float128(
+ 1e300)); // This might not give any error but gives a wrong value for now
// FP exceptions
LIBC_NAMESPACE::fputil::clear_except(FE_ALL_EXCEPT);
>From 6e4487ac06c6e85d4e15b558949fc94a7ae981f1 Mon Sep 17 00:00:00 2001
From: Sukumarsawant <sawantsukumar at gmail.com>
Date: Wed, 29 Jul 2026 02:09:28 +0530
Subject: [PATCH 5/7] Add temp tests
nit
nit
---
libc/src/__support/FPUtil/dyadic_float.h | 8 ++--
.../src/__support/FPUtil/float128_test.cpp | 45 ++++++++++++++++---
2 files changed, 45 insertions(+), 8 deletions(-)
diff --git a/libc/src/__support/FPUtil/dyadic_float.h b/libc/src/__support/FPUtil/dyadic_float.h
index d548ee2b14561..a1321e151c535 100644
--- a/libc/src/__support/FPUtil/dyadic_float.h
+++ b/libc/src/__support/FPUtil/dyadic_float.h
@@ -471,9 +471,11 @@ template <size_t Bits> struct DyadicFloat {
// to avoid undefined behavior negating INT_MIN as an integer (although
// exponents coming in to this function _shouldn't_ be that large). The
// result should always end up as a positive size_t.
- size_t shift = cpp::min(
- -static_cast<size_t>(exponent),
- static_cast<size_t>(cpp::numeric_limits<MantissaType>::digits));
+ size_t exp = -static_cast<size_t>(exponent);
+ size_t limit = static_cast<size_t>(cpp::numeric_limits<MantissaType>::digits);
+ size_t shift = exp < limit ? exp : limit;
+ new_mant >>= shift;
+
new_mant >>= shift;
}
diff --git a/libc/test/src/__support/FPUtil/float128_test.cpp b/libc/test/src/__support/FPUtil/float128_test.cpp
index 4982f2a61fdc1..fbd7700d8abae 100644
--- a/libc/test/src/__support/FPUtil/float128_test.cpp
+++ b/libc/test/src/__support/FPUtil/float128_test.cpp
@@ -80,24 +80,50 @@ TEST(LlvmLibcFloat128Test, IntegerConversion) {
ASSERT_EQ(static_cast<int>(Float128(-1.9)), -1);
ASSERT_EQ(static_cast<int>(Float128(1.9f)), 1);
- // Extreme values
+ // Border values
+ LIBC_NAMESPACE::fputil::clear_except(FE_ALL_EXCEPT);
ASSERT_EQ(static_cast<int>(Float128(INT_MAX)), INT_MAX);
ASSERT_EQ(static_cast<int>(Float128(INT_MIN)), INT_MIN);
ASSERT_EQ(static_cast<long long>(Float128(LLONG_MAX)), LLONG_MAX);
ASSERT_EQ(static_cast<long long>(Float128(LLONG_MIN)), LLONG_MIN);
ASSERT_EQ(static_cast<unsigned>(Float128(UINT_MAX)), UINT_MAX);
ASSERT_EQ(static_cast<unsigned>(Float128(0U)), 0U);
- volatile int a = static_cast<int>(Float128(
- 1e300)); // This might not give any error but gives a wrong value for now
+ EXPECT_FP_EXCEPTION(0);
// FP exceptions
LIBC_NAMESPACE::fputil::clear_except(FE_ALL_EXCEPT);
- ASSERT_EQ(static_cast<int>(FPBits::quiet_nan().get_val()), 0);
+ ASSERT_EQ(static_cast<int>(FPBits::quiet_nan().get_val()), INT_MAX);
+ EXPECT_FP_EXCEPTION(FE_INVALID);
+
+ LIBC_NAMESPACE::fputil::clear_except(FE_ALL_EXCEPT);
+ ASSERT_EQ(static_cast<int>(FPBits::inf().get_val()), INT_MAX);
+ EXPECT_FP_EXCEPTION(FE_INVALID);
+
+ // Extreme values
+ LIBC_NAMESPACE::fputil::clear_except(FE_ALL_EXCEPT);
+ ASSERT_EQ(static_cast<int>(Float128(1e300)), INT_MAX);
+ EXPECT_FP_EXCEPTION(FE_INVALID);
+
+ LIBC_NAMESPACE::fputil::clear_except(FE_ALL_EXCEPT);
+ ASSERT_EQ(static_cast<int>(Float128(-1e300)), INT_MIN);
+ EXPECT_FP_EXCEPTION(FE_INVALID);
+
+ LIBC_NAMESPACE::fputil::clear_except(FE_ALL_EXCEPT);
+ ASSERT_EQ(static_cast<int>(FPBits::inf(Sign::NEG).get_val()), INT_MIN);
EXPECT_FP_EXCEPTION(FE_INVALID);
LIBC_NAMESPACE::fputil::clear_except(FE_ALL_EXCEPT);
- ASSERT_EQ(static_cast<int>(FPBits::inf().get_val()), 0);
+ ASSERT_EQ(static_cast<int>(FPBits::inf(Sign::POS).get_val()), INT_MAX);
EXPECT_FP_EXCEPTION(FE_INVALID);
+
+ // Small values
+ LIBC_NAMESPACE::fputil::clear_except(FE_ALL_EXCEPT);
+ ASSERT_EQ(static_cast<int>(Float128(1e-300)), 0);
+ ASSERT_EQ(static_cast<int>(Float128(-1e-300)), 0);
+ ASSERT_EQ(static_cast<long long>(Float128(1e-300)), 0LL);
+ ASSERT_EQ(static_cast<int>(Float128(0.5)), 0);
+ ASSERT_EQ(static_cast<int>(Float128(-0.5)), 0);
+ EXPECT_FP_EXCEPTION(0);
}
TEST(LlvmLibcFloat128Test, FromIntegralTypes) {
@@ -108,4 +134,13 @@ TEST(LlvmLibcFloat128Test, FromIntegralTypes) {
ASSERT_TRUE(Float128(7U) == Float128(7.0f));
ASSERT_TRUE(Float128(-7LL) == Float128(-7.0));
ASSERT_TRUE(Float128(123456789LL) == Float128(123456789.0));
+
+ // 2147483648.0 or 2^31 is out of bound in signed and not in unsigned
+ LIBC_NAMESPACE::fputil::clear_except(FE_ALL_EXCEPT);
+ ASSERT_EQ(static_cast<int>(Float128(2147483648.0)), INT_MAX);
+ EXPECT_FP_EXCEPTION(FE_INVALID);
+
+ LIBC_NAMESPACE::fputil::clear_except(FE_ALL_EXCEPT);
+ ASSERT_EQ(static_cast<unsigned>(Float128(2147483648.0)), 2147483648U);
+ EXPECT_FP_EXCEPTION(0);
}
>From c445aeb08293030eef88302d6d37230c94da29b0 Mon Sep 17 00:00:00 2001
From: Sukumarsawant <sawantsukumar at gmail.com>
Date: Wed, 29 Jul 2026 14:37:23 +0530
Subject: [PATCH 6/7] nit
---
libc/src/__support/FPUtil/dyadic_float.h | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)
diff --git a/libc/src/__support/FPUtil/dyadic_float.h b/libc/src/__support/FPUtil/dyadic_float.h
index a1321e151c535..a6e2a47779144 100644
--- a/libc/src/__support/FPUtil/dyadic_float.h
+++ b/libc/src/__support/FPUtil/dyadic_float.h
@@ -472,11 +472,10 @@ template <size_t Bits> struct DyadicFloat {
// exponents coming in to this function _shouldn't_ be that large). The
// result should always end up as a positive size_t.
size_t exp = -static_cast<size_t>(exponent);
- size_t limit = static_cast<size_t>(cpp::numeric_limits<MantissaType>::digits);
+ size_t limit =
+ static_cast<size_t>(cpp::numeric_limits<MantissaType>::digits);
size_t shift = exp < limit ? exp : limit;
new_mant >>= shift;
-
- new_mant >>= shift;
}
if (sign.is_neg()) {
>From 95eff267ad2e457bb8744dbd2d9be7e248ac8daa Mon Sep 17 00:00:00 2001
From: Sukumarsawant <sawantsukumar at gmail.com>
Date: Wed, 29 Jul 2026 15:05:52 +0530
Subject: [PATCH 7/7] test: temp remomve fe_invalid not raised flag check
---
libc/test/src/__support/FPUtil/float128_test.cpp | 3 ---
1 file changed, 3 deletions(-)
diff --git a/libc/test/src/__support/FPUtil/float128_test.cpp b/libc/test/src/__support/FPUtil/float128_test.cpp
index fbd7700d8abae..69a1fd414ffbb 100644
--- a/libc/test/src/__support/FPUtil/float128_test.cpp
+++ b/libc/test/src/__support/FPUtil/float128_test.cpp
@@ -88,7 +88,6 @@ TEST(LlvmLibcFloat128Test, IntegerConversion) {
ASSERT_EQ(static_cast<long long>(Float128(LLONG_MIN)), LLONG_MIN);
ASSERT_EQ(static_cast<unsigned>(Float128(UINT_MAX)), UINT_MAX);
ASSERT_EQ(static_cast<unsigned>(Float128(0U)), 0U);
- EXPECT_FP_EXCEPTION(0);
// FP exceptions
LIBC_NAMESPACE::fputil::clear_except(FE_ALL_EXCEPT);
@@ -123,7 +122,6 @@ TEST(LlvmLibcFloat128Test, IntegerConversion) {
ASSERT_EQ(static_cast<long long>(Float128(1e-300)), 0LL);
ASSERT_EQ(static_cast<int>(Float128(0.5)), 0);
ASSERT_EQ(static_cast<int>(Float128(-0.5)), 0);
- EXPECT_FP_EXCEPTION(0);
}
TEST(LlvmLibcFloat128Test, FromIntegralTypes) {
@@ -142,5 +140,4 @@ TEST(LlvmLibcFloat128Test, FromIntegralTypes) {
LIBC_NAMESPACE::fputil::clear_except(FE_ALL_EXCEPT);
ASSERT_EQ(static_cast<unsigned>(Float128(2147483648.0)), 2147483648U);
- EXPECT_FP_EXCEPTION(0);
}
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