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[libc][math] Add test and fix atan2f crashing when flush-denorm-to-zero (FTZ) and denorm-as-zero (DAZ) modes are set. #112828

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Merged
merged 1 commit into from
Oct 18, 2024
Merged

[libc][math] Add test and fix atan2f crashing when flush-denorm-to-zero (FTZ) and denorm-as-zero (DAZ) modes are set. #112828

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14 changes: 9 additions & 5 deletions libc/src/math/generic/atan2f.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -246,12 +246,18 @@ LLVM_LIBC_FUNCTION(float, atan2f, (float y, float x)) {
uint32_t y_abs = y_bits.uintval();
uint32_t max_abs = x_abs > y_abs ? x_abs : y_abs;
uint32_t min_abs = x_abs <= y_abs ? x_abs : y_abs;
float num_f = FPBits(min_abs).get_val();
float den_f = FPBits(max_abs).get_val();
double num_d = static_cast<double>(num_f);
double den_d = static_cast<double>(den_f);

if (LIBC_UNLIKELY(max_abs >= 0x7f80'0000U || min_abs == 0U)) {
if (LIBC_UNLIKELY(max_abs >= 0x7f80'0000U || num_d == 0.0)) {
if (x_bits.is_nan() || y_bits.is_nan())
return FPBits::quiet_nan().get_val();
size_t x_except = x_abs == 0 ? 0 : (x_abs == 0x7f80'0000 ? 2 : 1);
size_t y_except = y_abs == 0 ? 0 : (y_abs == 0x7f80'0000 ? 2 : 1);
double x_d = static_cast<double>(x);
double y_d = static_cast<double>(y);
size_t x_except = (x_d == 0.0) ? 0 : (x_abs == 0x7f80'0000 ? 2 : 1);
size_t y_except = (y_d == 0.0) ? 0 : (y_abs == 0x7f80'0000 ? 2 : 1);

// Exceptional cases:
// EXCEPT[y_except][x_except][x_is_neg]
Expand All @@ -275,8 +281,6 @@ LLVM_LIBC_FUNCTION(float, atan2f, (float y, float x)) {
bool recip = x_abs < y_abs;
double final_sign = IS_NEG[(x_sign != y_sign) != recip];
fputil::DoubleDouble const_term = CONST_ADJ[x_sign][y_sign][recip];
double num_d = static_cast<double>(FPBits(min_abs).get_val());
double den_d = static_cast<double>(FPBits(max_abs).get_val());
double q_d = num_d / den_d;

double k_d = fputil::nearest_integer(q_d * 0x1.0p4f);
Expand Down
26 changes: 26 additions & 0 deletions libc/test/UnitTest/FPMatcher.h
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Expand Up @@ -15,6 +15,7 @@
#include "src/__support/FPUtil/FPBits.h"
#include "src/__support/FPUtil/fpbits_str.h"
#include "src/__support/macros/config.h"
#include "src/__support/macros/properties/architectures.h"
#include "test/UnitTest/RoundingModeUtils.h"
#include "test/UnitTest/StringUtils.h"
#include "test/UnitTest/Test.h"
Expand Down Expand Up @@ -175,6 +176,31 @@ template <typename T> struct FPTest : public Test {
};
};

// Add facility to test Flush-Denormal-To-Zero (FTZ) and Denormal-As-Zero (DAZ)
// modes.
// These tests to ensure that our implementations will not crash under these
// modes.
#if defined(LIBC_TARGET_ARCH_IS_X86_64) && __has_builtin(__builtin_ia32_stmxcsr)

#define LIBC_TEST_FTZ_DAZ

static constexpr unsigned FTZ = 0x8000; // Flush denormal to zero
static constexpr unsigned DAZ = 0x0040; // Denormal as zero

struct ModifyMXCSR {
ModifyMXCSR(unsigned flags) {
old_mxcsr = __builtin_ia32_stmxcsr();
__builtin_ia32_ldmxcsr(old_mxcsr | flags);
}

~ModifyMXCSR() { __builtin_ia32_ldmxcsr(old_mxcsr); }

private:
unsigned old_mxcsr;
};

#endif

} // namespace testing
} // namespace LIBC_NAMESPACE_DECL

Expand Down
37 changes: 37 additions & 0 deletions libc/test/src/math/smoke/atan2f_test.cpp
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Expand Up @@ -58,3 +58,40 @@ TEST_F(LlvmLibcAtan2fTest, SpecialNumbers) {
// EXPECT_FP_EXCEPTION(0);
EXPECT_MATH_ERRNO(0);
}

#ifdef LIBC_TEST_FTZ_DAZ

using namespace LIBC_NAMESPACE::testing;

TEST_F(LlvmLibcAtan2fTest, FTZMode) {
ModifyMXCSR mxcsr(FTZ);

EXPECT_FP_EQ(0x1.921fb6p-1f,
LIBC_NAMESPACE::atan2f(min_denormal, min_denormal));
EXPECT_FP_EQ(0x1.000002p-23f,
LIBC_NAMESPACE::atan2f(min_denormal, max_denormal));
EXPECT_FP_EQ(0x1.921fb4p0f,
LIBC_NAMESPACE::atan2f(max_denormal, min_denormal));
EXPECT_FP_EQ(0x1.921fb6p-1f,
LIBC_NAMESPACE::atan2f(max_denormal, max_denormal));
}

TEST_F(LlvmLibcAtan2fTest, DAZMode) {
ModifyMXCSR mxcsr(DAZ);

EXPECT_FP_EQ(0.0f, LIBC_NAMESPACE::atan2f(min_denormal, min_denormal));
EXPECT_FP_EQ(0.0f, LIBC_NAMESPACE::atan2f(min_denormal, max_denormal));
EXPECT_FP_EQ(0.0f, LIBC_NAMESPACE::atan2f(max_denormal, min_denormal));
EXPECT_FP_EQ(0.0f, LIBC_NAMESPACE::atan2f(max_denormal, max_denormal));
}

TEST_F(LlvmLibcAtan2fTest, FTZDAZMode) {
ModifyMXCSR mxcsr(FTZ | DAZ);

EXPECT_FP_EQ(0.0f, LIBC_NAMESPACE::atan2f(min_denormal, min_denormal));
EXPECT_FP_EQ(0.0f, LIBC_NAMESPACE::atan2f(min_denormal, max_denormal));
EXPECT_FP_EQ(0.0f, LIBC_NAMESPACE::atan2f(max_denormal, min_denormal));
EXPECT_FP_EQ(0.0f, LIBC_NAMESPACE::atan2f(max_denormal, max_denormal));
}

#endif
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