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[libc][math] Adjust rsqrtf16 exception checks. #159411

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Merged
merged 1 commit into from
Sep 17, 2025
Merged

[libc][math] Adjust rsqrtf16 exception checks. #159411

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51 changes: 27 additions & 24 deletions libc/src/__support/math/rsqrtf16.h
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Original file line number Diff line number Diff line change
Expand Up @@ -28,36 +28,39 @@ LIBC_INLINE static constexpr float16 rsqrtf16(float16 x) {
using FPBits = fputil::FPBits<float16>;
FPBits xbits(x);

const uint16_t x_u = xbits.uintval();
const uint16_t x_abs = x_u & 0x7fff;
const uint16_t x_sign = x_u >> 15;
uint16_t x_u = xbits.uintval();
uint16_t x_abs = x_u & 0x7fff;

constexpr uint16_t INF_BIT = FPBits::inf().uintval();

// x is 0, inf/nan, or negative.
if (LIBC_UNLIKELY(x_u == 0 || x_u >= INF_BIT)) {
// x is NaN
if (x_abs > INF_BIT) {
if (xbits.is_signaling_nan()) {
fputil::raise_except_if_required(FE_INVALID);
return FPBits::quiet_nan().get_val();
}
return x;
}

// |x| = 0
if (x_abs == 0) {
fputil::raise_except_if_required(FE_DIVBYZERO);
fputil::set_errno_if_required(ERANGE);
return FPBits::inf(xbits.sign()).get_val();
}

// x is NaN
if (LIBC_UNLIKELY(xbits.is_nan())) {
if (xbits.is_signaling_nan()) {
// -inf <= x < 0
if (x_u > 0x7fff) {
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in future: We should replace these magic constants with proper variable names, or provide a way for fpbits to give these values directly.

fputil::raise_except_if_required(FE_INVALID);
fputil::set_errno_if_required(EDOM);
return FPBits::quiet_nan().get_val();
}
return x;
}

// |x| = 0
if (LIBC_UNLIKELY(x_abs == 0x0)) {
fputil::raise_except_if_required(FE_DIVBYZERO);
fputil::set_errno_if_required(ERANGE);
return FPBits::inf(Sign::POS).get_val();
}

// -inf <= x < 0
if (LIBC_UNLIKELY(x_sign == 1)) {
fputil::raise_except_if_required(FE_INVALID);
fputil::set_errno_if_required(EDOM);
return FPBits::quiet_nan().get_val();
}

// x = +inf => rsqrt(x) = 0
if (LIBC_UNLIKELY(xbits.is_inf()))
// x = +inf => rsqrt(x) = 0
return FPBits::zero().get_val();
}

// TODO: add integer based implementation when LIBC_TARGET_CPU_HAS_FPU_FLOAT
// is not defined
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5 changes: 3 additions & 2 deletions libc/test/src/math/rsqrtf16_test.cpp
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Expand Up @@ -19,8 +19,9 @@ namespace mpfr = LIBC_NAMESPACE::testing::mpfr;
static constexpr uint16_t POS_START = 0x0000U;
static constexpr uint16_t POS_STOP = 0x7c00U;

// Range: [-Inf, 0]
static constexpr uint16_t NEG_START = 0x8000U;
// Range: [-Inf, 0)
// rsqrt(-0.0) is -inf, not the same for mpfr.
static constexpr uint16_t NEG_START = 0x8001U;
static constexpr uint16_t NEG_STOP = 0xfc00U;

TEST_F(LlvmLibcRsqrtf16Test, PositiveRange) {
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19 changes: 14 additions & 5 deletions libc/test/src/math/smoke/rsqrtf16_test.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -7,30 +7,39 @@
//===----------------------------------------------------------------------===//

#include "hdr/errno_macros.h"
#include "src/__support/FPUtil/cast.h"
#include "src/math/rsqrtf16.h"
#include "test/UnitTest/FPMatcher.h"
#include "test/UnitTest/Test.h"

using LlvmLibcRsqrtf16Test = LIBC_NAMESPACE::testing::FPTest<float16>;
using LIBC_NAMESPACE::fputil::cast;

TEST_F(LlvmLibcRsqrtf16Test, SpecialNumbers) {
EXPECT_FP_EQ(aNaN, LIBC_NAMESPACE::rsqrtf16(aNaN));
EXPECT_MATH_ERRNO(0);

EXPECT_FP_EQ_WITH_EXCEPTION(aNaN, LIBC_NAMESPACE::rsqrtf16(sNaN), FE_INVALID);
EXPECT_FP_IS_NAN_WITH_EXCEPTION(LIBC_NAMESPACE::rsqrtf16(sNaN), FE_INVALID);
EXPECT_MATH_ERRNO(0);

EXPECT_FP_EQ(inf, LIBC_NAMESPACE::rsqrtf16(0.0f));
EXPECT_FP_EQ(inf, LIBC_NAMESPACE::rsqrtf16(zero));
EXPECT_MATH_ERRNO(ERANGE);

EXPECT_FP_EQ(neg_inf, LIBC_NAMESPACE::rsqrtf16(neg_zero));
EXPECT_MATH_ERRNO(ERANGE);

EXPECT_FP_EQ(1.0f, LIBC_NAMESPACE::rsqrtf16(1.0f));
EXPECT_FP_EQ(
LIBC_NAMESPACE::fputil::cast<float16>(1.0f),
LIBC_NAMESPACE::rsqrtf16(LIBC_NAMESPACE::fputil::cast<float16>(1.0f)));
EXPECT_MATH_ERRNO(0);

EXPECT_FP_EQ(0.0f, LIBC_NAMESPACE::rsqrtf16(inf));
EXPECT_FP_EQ(zero, LIBC_NAMESPACE::rsqrtf16(inf));
EXPECT_MATH_ERRNO(0);

EXPECT_FP_EQ(aNaN, LIBC_NAMESPACE::rsqrtf16(neg_inf));
EXPECT_MATH_ERRNO(EDOM);

EXPECT_FP_EQ(aNaN, LIBC_NAMESPACE::rsqrtf16(-2.0f));
EXPECT_FP_EQ(aNaN, LIBC_NAMESPACE::rsqrtf16(
LIBC_NAMESPACE::fputil::cast<float16>(-2.0f)));
EXPECT_MATH_ERRNO(EDOM);
}
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