[libc][NFC] Split str_to_float tests and reduce type clutter (#75471)

This is a follow up on #75353.

5 files changed, 300 insertions, 286 deletions

diff --git a/libc/test/src/__support/CMakeLists.txt b/libc/test/src/__support/CMakeLists.txt
index 740209b..fe8b3c4 100644
--- a/libc/test/src/__support/CMakeLists.txt
+++ b/libc/test/src/__support/CMakeLists.txt
@@ -50,6 +50,8 @@ add_libc_test(
     libc-support-tests
   SRCS
     str_to_float_test.cpp
+    str_to_double_test.cpp
+    str_to_long_double_test.cpp
   DEPENDS
     libc.src.__support.str_to_float
     libc.src.__support.uint128
diff --git a/libc/test/src/__support/str_to_double_test.cpp b/libc/test/src/__support/str_to_double_test.cpp
new file mode 100644
index 0000000..b66935f
--- /dev/null
+++ b/libc/test/src/__support/str_to_double_test.cpp
@@ -0,0 +1,105 @@
+#include "str_to_fp_test.h"
+
+namespace LIBC_NAMESPACE {
+using LlvmLibcStrToDblTest = LlvmLibcStrToFloatTest<double>;
+
+TEST_F(LlvmLibcStrToDblTest, ClingerFastPathFloat64Simple) {
+  clinger_fast_path_test(123, 0, 0xEC00000000000, 1029);
+  clinger_fast_path_test(1234567890123456, 1, 0x5ee2a2eb5a5c0, 1076);
+  clinger_fast_path_test(1234567890, -10, 0xf9add3739635f, 1019);
+}
+
+TEST_F(LlvmLibcStrToDblTest, ClingerFastPathFloat64ExtendedExp) {
+  clinger_fast_path_test(1, 30, 0x93e5939a08cea, 1122);
+  clinger_fast_path_test(1, 37, 0xe17b84357691b, 1145);
+  clinger_fast_path_fails_test(10, 37);
+  clinger_fast_path_fails_test(1, 100);
+}
+
+TEST_F(LlvmLibcStrToDblTest, ClingerFastPathFloat64NegativeExp) {
+  clinger_fast_path_test(1, -10, 0xb7cdfd9d7bdbb, 989);
+  clinger_fast_path_test(1, -20, 0x79ca10c924223, 956);
+  clinger_fast_path_fails_test(1, -25);
+}
+
+TEST_F(LlvmLibcStrToDblTest, EiselLemireFloat64Simple) {
+  eisel_lemire_test(12345678901234567890u, 1, 0x1AC53A7E04BCDA, 1089);
+  eisel_lemire_test(123, 0, 0x1EC00000000000, 1029);
+  eisel_lemire_test(12345678901234568192u, 0, 0x156A95319D63E2, 1086);
+}
+
+TEST_F(LlvmLibcStrToDblTest, EiselLemireFloat64SpecificFailures) {
+  // These test cases have caused failures in the past.
+  eisel_lemire_test(358416272, -33, 0x1BBB2A68C9D0B9, 941);
+  eisel_lemire_test(2166568064000000238u, -9, 0x10246690000000, 1054);
+  eisel_lemire_test(2794967654709307187u, 1, 0x183e132bc608c8, 1087);
+  eisel_lemire_test(2794967654709307188u, 1, 0x183e132bc608c9, 1087);
+}
+
+// Check the fallback states for the algorithm:
+TEST_F(LlvmLibcStrToDblTest, EiselLemireFallbackStates) {
+  // This number can't be evaluated by Eisel-Lemire since it's exactly 1024 away
+  // from both of its closest floating point approximations
+  // (12345678901234548736 and 12345678901234550784)
+  ASSERT_FALSE(
+      internal::eisel_lemire<double>({12345678901234549760u, 0}).has_value());
+}
+
+TEST_F(LlvmLibcStrToDblTest, SimpleDecimalConversion64BasicWholeNumbers) {
+  simple_decimal_conversion_test("123456789012345678900", 0x1AC53A7E04BCDA,
+                                 1089);
+  simple_decimal_conversion_test("123", 0x1EC00000000000, 1029);
+  simple_decimal_conversion_test("12345678901234549760", 0x156A95319D63D8,
+                                 1086);
+}
+
+TEST_F(LlvmLibcStrToDblTest, SimpleDecimalConversion64BasicDecimals) {
+  simple_decimal_conversion_test("1.2345", 0x13c083126e978d, 1023);
+  simple_decimal_conversion_test(".2345", 0x1e04189374bc6a, 1020);
+  simple_decimal_conversion_test(".299792458", 0x132fccb4aca314, 1021);
+}
+
+TEST_F(LlvmLibcStrToDblTest, SimpleDecimalConversion64BasicExponents) {
+  simple_decimal_conversion_test("1e10", 0x12a05f20000000, 1056);
+  simple_decimal_conversion_test("1e-10", 0x1b7cdfd9d7bdbb, 989);
+  simple_decimal_conversion_test("1e300", 0x17e43c8800759c, 2019);
+  simple_decimal_conversion_test("1e-300", 0x156e1fc2f8f359, 26);
+}
+
+TEST_F(LlvmLibcStrToDblTest, SimpleDecimalConversion64BasicSubnormals) {
+  simple_decimal_conversion_test("1e-320", 0x7e8, 0, ERANGE);
+  simple_decimal_conversion_test("1e-308", 0x730d67819e8d2, 0, ERANGE);
+  simple_decimal_conversion_test("2.9e-308", 0x14da6df5e4bcc8, 1);
+}
+
+TEST_F(LlvmLibcStrToDblTest, SimpleDecimalConversion64SubnormalRounding) {
+
+  // Technically you can keep adding digits until you hit the truncation limit,
+  // but this is the shortest string that results in the maximum subnormal that
+  // I found.
+  simple_decimal_conversion_test("2.225073858507201e-308", 0xfffffffffffff, 0,
+                                 ERANGE);
+
+  // Same here, if you were to extend the max subnormal out for another 800
+  // digits, incrementing any one of those digits would create a normal number.
+  simple_decimal_conversion_test("2.2250738585072012e-308", 0x10000000000000,
+                                 1);
+}
+
+TEST(LlvmLibcStrToDblTest, SimpleDecimalConversionExtraTypes) {
+  uint64_t double_output_mantissa = 0;
+  uint32_t output_exp2 = 0;
+
+  libc_errno = 0;
+  auto double_result =
+      internal::simple_decimal_conversion<double>("123456789012345678900");
+
+  double_output_mantissa = double_result.num.mantissa;
+  output_exp2 = double_result.num.exponent;
+
+  EXPECT_EQ(double_output_mantissa, uint64_t(0x1AC53A7E04BCDA));
+  EXPECT_EQ(output_exp2, uint32_t(1089));
+  EXPECT_EQ(double_result.error, 0);
+}
+
+} // namespace LIBC_NAMESPACE
diff --git a/libc/test/src/__support/str_to_float_test.cpp b/libc/test/src/__support/str_to_float_test.cpp
index 35f7318..3102fa7 100644
--- a/libc/test/src/__support/str_to_float_test.cpp
+++ b/libc/test/src/__support/str_to_float_test.cpp
@@ -1,321 +1,59 @@
-//===-- Unittests for str_to_float ----------------------------------------===//
-//
-// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
-// See https://llvm.org/LICENSE.txt for license information.
-// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-//
-//===----------------------------------------------------------------------===//
+#include "str_to_fp_test.h"
 
-#include "src/__support/FPUtil/FPBits.h"
-#include "src/__support/UInt128.h"
-#include "src/__support/str_to_float.h"
-#include "src/errno/libc_errno.h"
+namespace LIBC_NAMESPACE {
 
-#include "test/UnitTest/Test.h"
+using LlvmLibcStrToFltTest = LlvmLibcStrToFloatTest<float>;
 
-class LlvmLibcStrToFloatTest : public LIBC_NAMESPACE::testing::Test {
-public:
-  template <class T>
-  void clinger_fast_path_test(
-      const typename LIBC_NAMESPACE::fputil::FPBits<T>::UIntType inputMantissa,
-      const int32_t inputExp10,
-      const typename LIBC_NAMESPACE::fputil::FPBits<T>::UIntType
-          expectedOutputMantissa,
-      const uint32_t expectedOutputExp2) {
-    typename LIBC_NAMESPACE::fputil::FPBits<T>::UIntType
-        actual_output_mantissa = 0;
-    uint32_t actual_output_exp2 = 0;
-
-    auto result = LIBC_NAMESPACE::internal::clinger_fast_path<T>(
-        {inputMantissa, inputExp10});
-
-    ASSERT_TRUE(result.has_value());
-
-    actual_output_mantissa = result->mantissa;
-    actual_output_exp2 = result->exponent;
-
-    EXPECT_EQ(actual_output_mantissa, expectedOutputMantissa);
-    EXPECT_EQ(actual_output_exp2, expectedOutputExp2);
-  }
-
-  template <class T>
-  void clinger_fast_path_fails_test(
-      const typename LIBC_NAMESPACE::fputil::FPBits<T>::UIntType inputMantissa,
-      const int32_t inputExp10) {
-    ASSERT_FALSE(LIBC_NAMESPACE::internal::clinger_fast_path<T>(
-                     {inputMantissa, inputExp10})
-                     .has_value());
-  }
-
-  template <class T>
-  void eisel_lemire_test(
-      const typename LIBC_NAMESPACE::fputil::FPBits<T>::UIntType inputMantissa,
-      const int32_t inputExp10,
-      const typename LIBC_NAMESPACE::fputil::FPBits<T>::UIntType
-          expectedOutputMantissa,
-      const uint32_t expectedOutputExp2) {
-    typename LIBC_NAMESPACE::fputil::FPBits<T>::UIntType
-        actual_output_mantissa = 0;
-    uint32_t actual_output_exp2 = 0;
-
-    auto result =
-        LIBC_NAMESPACE::internal::eisel_lemire<T>({inputMantissa, inputExp10});
-
-    ASSERT_TRUE(result.has_value());
-
-    actual_output_mantissa = result->mantissa;
-    actual_output_exp2 = result->exponent;
-
-    EXPECT_EQ(actual_output_mantissa, expectedOutputMantissa);
-    EXPECT_EQ(actual_output_exp2, expectedOutputExp2);
-  }
-
-  template <class T>
-  void simple_decimal_conversion_test(
-      const char *__restrict numStart,
-      const typename LIBC_NAMESPACE::fputil::FPBits<T>::UIntType
-          expectedOutputMantissa,
-      const uint32_t expectedOutputExp2, const int expectedErrno = 0) {
-    typename LIBC_NAMESPACE::fputil::FPBits<T>::UIntType
-        actual_output_mantissa = 0;
-    uint32_t actual_output_exp2 = 0;
-    libc_errno = 0;
-
-    auto result =
-        LIBC_NAMESPACE::internal::simple_decimal_conversion<T>(numStart);
-
-    actual_output_mantissa = result.num.mantissa;
-    actual_output_exp2 = result.num.exponent;
-
-    EXPECT_EQ(actual_output_mantissa, expectedOutputMantissa);
-    EXPECT_EQ(actual_output_exp2, expectedOutputExp2);
-    EXPECT_EQ(result.error, expectedErrno);
-  }
-};
-
-TEST_F(LlvmLibcStrToFloatTest, ClingerFastPathFloat64Simple) {
-  clinger_fast_path_test<double>(123, 0, 0xEC00000000000, 1029);
-  clinger_fast_path_test<double>(1234567890123456, 1, 0x5ee2a2eb5a5c0, 1076);
-  clinger_fast_path_test<double>(1234567890, -10, 0xf9add3739635f, 1019);
+TEST_F(LlvmLibcStrToFltTest, ClingerFastPathFloat32Simple) {
+  clinger_fast_path_test(123, 0, 0x760000, 133);
+  clinger_fast_path_test(1234567, 1, 0x3c6146, 150);
+  clinger_fast_path_test(12345, -5, 0x7cd35b, 123);
 }
 
-TEST_F(LlvmLibcStrToFloatTest, ClingerFastPathFloat64ExtendedExp) {
-  clinger_fast_path_test<double>(1, 30, 0x93e5939a08cea, 1122);
-  clinger_fast_path_test<double>(1, 37, 0xe17b84357691b, 1145);
-  clinger_fast_path_fails_test<double>(10, 37);
-  clinger_fast_path_fails_test<double>(1, 100);
+TEST_F(LlvmLibcStrToFltTest, ClingerFastPathFloat32ExtendedExp) {
+  clinger_fast_path_test(1, 15, 0x635fa9, 176);
+  clinger_fast_path_test(1, 17, 0x31a2bc, 183);
+  clinger_fast_path_fails_test(10, 17);
+  clinger_fast_path_fails_test(1, 50);
 }
 
-TEST_F(LlvmLibcStrToFloatTest, ClingerFastPathFloat64NegativeExp) {
-  clinger_fast_path_test<double>(1, -10, 0xb7cdfd9d7bdbb, 989);
-  clinger_fast_path_test<double>(1, -20, 0x79ca10c924223, 956);
-  clinger_fast_path_fails_test<double>(1, -25);
-}
-
-TEST_F(LlvmLibcStrToFloatTest, ClingerFastPathFloat32Simple) {
-  clinger_fast_path_test<float>(123, 0, 0x760000, 133);
-  clinger_fast_path_test<float>(1234567, 1, 0x3c6146, 150);
-  clinger_fast_path_test<float>(12345, -5, 0x7cd35b, 123);
-}
-
-TEST_F(LlvmLibcStrToFloatTest, ClingerFastPathFloat32ExtendedExp) {
-  clinger_fast_path_test<float>(1, 15, 0x635fa9, 176);
-  clinger_fast_path_test<float>(1, 17, 0x31a2bc, 183);
-  clinger_fast_path_fails_test<float>(10, 17);
-  clinger_fast_path_fails_test<float>(1, 50);
-}
-
-TEST_F(LlvmLibcStrToFloatTest, ClingerFastPathFloat32NegativeExp) {
-  clinger_fast_path_test<float>(1, -5, 0x27c5ac, 110);
-  clinger_fast_path_test<float>(1, -10, 0x5be6ff, 93);
-  clinger_fast_path_fails_test<float>(1, -15);
-}
-
-TEST_F(LlvmLibcStrToFloatTest, EiselLemireFloat64Simple) {
-  eisel_lemire_test<double>(12345678901234567890u, 1, 0x1AC53A7E04BCDA, 1089);
-  eisel_lemire_test<double>(123, 0, 0x1EC00000000000, 1029);
-  eisel_lemire_test<double>(12345678901234568192u, 0, 0x156A95319D63E2, 1086);
-}
-
-TEST_F(LlvmLibcStrToFloatTest, EiselLemireFloat64SpecificFailures) {
-  // These test cases have caused failures in the past.
-  eisel_lemire_test<double>(358416272, -33, 0x1BBB2A68C9D0B9, 941);
-  eisel_lemire_test<double>(2166568064000000238u, -9, 0x10246690000000, 1054);
-  eisel_lemire_test<double>(2794967654709307187u, 1, 0x183e132bc608c8, 1087);
-  eisel_lemire_test<double>(2794967654709307188u, 1, 0x183e132bc608c9, 1087);
+TEST_F(LlvmLibcStrToFltTest, ClingerFastPathFloat32NegativeExp) {
+  clinger_fast_path_test(1, -5, 0x27c5ac, 110);
+  clinger_fast_path_test(1, -10, 0x5be6ff, 93);
+  clinger_fast_path_fails_test(1, -15);
 }
 
 // Check the fallback states for the algorithm:
-TEST_F(LlvmLibcStrToFloatTest, EiselLemireFallbackStates) {
+TEST_F(LlvmLibcStrToFltTest, EiselLemireFallbackStates) {
   // This number can't be evaluated by Eisel-Lemire since it's exactly 1024 away
   // from both of its closest floating point approximations
   // (12345678901234548736 and 12345678901234550784)
-  ASSERT_FALSE(
-      LIBC_NAMESPACE::internal::eisel_lemire<double>({12345678901234549760u, 0})
-          .has_value());
-
-  ASSERT_FALSE(
-      LIBC_NAMESPACE::internal::eisel_lemire<float>({20040229, 0}).has_value());
+  ASSERT_FALSE(internal::eisel_lemire<float>({20040229, 0}).has_value());
 }
 
-TEST_F(LlvmLibcStrToFloatTest, SimpleDecimalConversion64BasicWholeNumbers) {
-  simple_decimal_conversion_test<double>("123456789012345678900",
-                                         0x1AC53A7E04BCDA, 1089);
-  simple_decimal_conversion_test<double>("123", 0x1EC00000000000, 1029);
-  simple_decimal_conversion_test<double>("12345678901234549760",
-                                         0x156A95319D63D8, 1086);
-}
-
-TEST_F(LlvmLibcStrToFloatTest, SimpleDecimalConversion64BasicDecimals) {
-  simple_decimal_conversion_test<double>("1.2345", 0x13c083126e978d, 1023);
-  simple_decimal_conversion_test<double>(".2345", 0x1e04189374bc6a, 1020);
-  simple_decimal_conversion_test<double>(".299792458", 0x132fccb4aca314, 1021);
-}
-
-TEST_F(LlvmLibcStrToFloatTest, SimpleDecimalConversion64BasicExponents) {
-  simple_decimal_conversion_test<double>("1e10", 0x12a05f20000000, 1056);
-  simple_decimal_conversion_test<double>("1e-10", 0x1b7cdfd9d7bdbb, 989);
-  simple_decimal_conversion_test<double>("1e300", 0x17e43c8800759c, 2019);
-  simple_decimal_conversion_test<double>("1e-300", 0x156e1fc2f8f359, 26);
-}
-
-TEST_F(LlvmLibcStrToFloatTest, SimpleDecimalConversion64BasicSubnormals) {
-  simple_decimal_conversion_test<double>("1e-320", 0x7e8, 0, ERANGE);
-  simple_decimal_conversion_test<double>("1e-308", 0x730d67819e8d2, 0, ERANGE);
-  simple_decimal_conversion_test<double>("2.9e-308", 0x14da6df5e4bcc8, 1);
-}
-
-TEST_F(LlvmLibcStrToFloatTest, SimpleDecimalConversion64SubnormalRounding) {
-
-  // Technically you can keep adding digits until you hit the truncation limit,
-  // but this is the shortest string that results in the maximum subnormal that
-  // I found.
-  simple_decimal_conversion_test<double>("2.225073858507201e-308",
-                                         0xfffffffffffff, 0, ERANGE);
-
-  // Same here, if you were to extend the max subnormal out for another 800
-  // digits, incrementing any one of those digits would create a normal number.
-  simple_decimal_conversion_test<double>("2.2250738585072012e-308",
-                                         0x10000000000000, 1);
-}
-
-TEST_F(LlvmLibcStrToFloatTest, SimpleDecimalConversion32SpecificFailures) {
-  simple_decimal_conversion_test<float>(
+TEST_F(LlvmLibcStrToFltTest, SimpleDecimalConversion32SpecificFailures) {
+  simple_decimal_conversion_test(
       "1.4012984643248170709237295832899161312802619418765e-45", 0x1, 0,
       ERANGE);
-  simple_decimal_conversion_test<float>(
+  simple_decimal_conversion_test(
       "7."
       "006492321624085354618647916449580656401309709382578858785341419448955413"
       "42930300743319094181060791015625e-46",
       0x0, 0, ERANGE);
 }
 
-TEST(LlvmLibcStrToFloatTest, SimpleDecimalConversionExtraTypes) {
+TEST(LlvmLibcStrToFltTest, SimpleDecimalConversionExtraTypes) {
   uint32_t float_output_mantissa = 0;
   uint32_t output_exp2 = 0;
 
   libc_errno = 0;
   auto float_result =
-      LIBC_NAMESPACE::internal::simple_decimal_conversion<float>(
-          "123456789012345678900");
+      internal::simple_decimal_conversion<float>("123456789012345678900");
   float_output_mantissa = float_result.num.mantissa;
   output_exp2 = float_result.num.exponent;
   EXPECT_EQ(float_output_mantissa, uint32_t(0xd629d4));
   EXPECT_EQ(output_exp2, uint32_t(193));
   EXPECT_EQ(float_result.error, 0);
-
-  uint64_t double_output_mantissa = 0;
-  output_exp2 = 0;
-
-  libc_errno = 0;
-  auto double_result =
-      LIBC_NAMESPACE::internal::simple_decimal_conversion<double>(
-          "123456789012345678900");
-
-  double_output_mantissa = double_result.num.mantissa;
-  output_exp2 = double_result.num.exponent;
-
-  EXPECT_EQ(double_output_mantissa, uint64_t(0x1AC53A7E04BCDA));
-  EXPECT_EQ(output_exp2, uint32_t(1089));
-  EXPECT_EQ(double_result.error, 0);
 }
 
-#if defined(LIBC_LONG_DOUBLE_IS_FLOAT64)
-TEST_F(LlvmLibcStrToFloatTest, EiselLemireFloat64AsLongDouble) {
-  eisel_lemire_test<long double>(123, 0, 0x1EC00000000000, 1029);
-}
-#elif defined(LIBC_LONG_DOUBLE_IS_X86_FLOAT80)
-TEST_F(LlvmLibcStrToFloatTest, EiselLemireFloat80Simple) {
-  eisel_lemire_test<long double>(123, 0, 0xf600000000000000, 16389);
-  eisel_lemire_test<long double>(12345678901234568192u, 0, 0xab54a98ceb1f0c00,
-                                 16446);
-}
-
-TEST_F(LlvmLibcStrToFloatTest, EiselLemireFloat80LongerMantissa) {
-  eisel_lemire_test<long double>((UInt128(0x1234567812345678) << 64) +
-                                     UInt128(0x1234567812345678),
-                                 0, 0x91a2b3c091a2b3c1, 16507);
-  eisel_lemire_test<long double>((UInt128(0x1234567812345678) << 64) +
-                                     UInt128(0x1234567812345678),
-                                 300, 0xd97757de56adb65c, 17503);
-  eisel_lemire_test<long double>((UInt128(0x1234567812345678) << 64) +
-                                     UInt128(0x1234567812345678),
-                                 -300, 0xc30feb9a7618457d, 15510);
-}
-
-// These tests check numbers at the edge of the DETAILED_POWERS_OF_TEN table.
-// This doesn't reach very far into the range for long doubles, since it's sized
-// for doubles and their 11 exponent bits, and not for long doubles and their
-// 15 exponent bits. This is a known tradeoff, and was made because a proper
-// long double table would be approximately 16 times longer (specifically the
-// maximum exponent would need to be about 5000, leading to a 10,000 entry
-// table). This would have significant memory and storage costs all the time to
-// speed up a relatively uncommon path.
-TEST_F(LlvmLibcStrToFloatTest, EiselLemireFloat80TableLimits) {
-  eisel_lemire_test<long double>(1, 347, 0xd13eb46469447567, 17535);
-  eisel_lemire_test<long double>(1, -348, 0xfa8fd5a0081c0288, 15226);
-}
-
-TEST_F(LlvmLibcStrToFloatTest, EiselLemireFloat80Fallback) {
-  // This number is halfway between two possible results, and the algorithm
-  // can't determine which is correct.
-  ASSERT_FALSE(LIBC_NAMESPACE::internal::eisel_lemire<long double>(
-                   {12345678901234567890u, 1})
-                   .has_value());
-
-  // These numbers' exponents are out of range for the current powers of ten
-  // table.
-  ASSERT_FALSE(LIBC_NAMESPACE::internal::eisel_lemire<long double>({1, 1000})
-                   .has_value());
-  ASSERT_FALSE(LIBC_NAMESPACE::internal::eisel_lemire<long double>({1, -1000})
-                   .has_value());
-}
-#else // Quad precision long double
-TEST_F(LlvmLibcStrToFloatTest, EiselLemireFloat128Simple) {
-  eisel_lemire_test<long double>(123, 0, (UInt128(0x1ec0000000000) << 64),
-                                 16389);
-  eisel_lemire_test<long double>(
-      12345678901234568192u, 0,
-      (UInt128(0x156a95319d63e) << 64) + UInt128(0x1800000000000000), 16446);
-}
-
-TEST_F(LlvmLibcStrToFloatTest, EiselLemireFloat128LongerMantissa) {
-  eisel_lemire_test<long double>(
-      (UInt128(0x1234567812345678) << 64) + UInt128(0x1234567812345678), 0,
-      (UInt128(0x1234567812345) << 64) + UInt128(0x6781234567812345), 16507);
-  eisel_lemire_test<long double>(
-      (UInt128(0x1234567812345678) << 64) + UInt128(0x1234567812345678), 300,
-      (UInt128(0x1b2eeafbcad5b) << 64) + UInt128(0x6cb8b4451dfcde19), 17503);
-  eisel_lemire_test<long double>(
-      (UInt128(0x1234567812345678) << 64) + UInt128(0x1234567812345678), -300,
-      (UInt128(0x1861fd734ec30) << 64) + UInt128(0x8afa7189f0f7595f), 15510);
-}
-
-TEST_F(LlvmLibcStrToFloatTest, EiselLemireFloat128Fallback) {
-  ASSERT_FALSE(
-      LIBC_NAMESPACE::internal::eisel_lemire<long double>(
-          {(UInt128(0x5ce0e9a56015fec5) << 64) + UInt128(0xaadfa328ae39b333),
-           1})
-          .has_value());
-}
-#endif
+} // namespace LIBC_NAMESPACE
diff --git a/libc/test/src/__support/str_to_fp_test.h b/libc/test/src/__support/str_to_fp_test.h
new file mode 100644
index 0000000..3b891fc
--- /dev/null
+++ b/libc/test/src/__support/str_to_fp_test.h
@@ -0,0 +1,81 @@
+//===-- Unittests for str_to_float ----------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/__support/FPUtil/FloatProperties.h"
+#include "src/__support/UInt128.h"
+#include "src/__support/str_to_float.h"
+#include "src/errno/libc_errno.h"
+
+#include "test/UnitTest/Test.h"
+
+namespace LIBC_NAMESPACE {
+
+template <typename T> struct LlvmLibcStrToFloatTest : public testing::Test {
+  using UIntType = typename fputil::FloatProperties<T>::UIntType;
+
+  void clinger_fast_path_test(const UIntType inputMantissa,
+                              const int32_t inputExp10,
+                              const UIntType expectedOutputMantissa,
+                              const uint32_t expectedOutputExp2) {
+    UIntType actual_output_mantissa = 0;
+    uint32_t actual_output_exp2 = 0;
+
+    auto result = internal::clinger_fast_path<T>({inputMantissa, inputExp10});
+
+    ASSERT_TRUE(result.has_value());
+
+    actual_output_mantissa = result->mantissa;
+    actual_output_exp2 = result->exponent;
+
+    EXPECT_EQ(actual_output_mantissa, expectedOutputMantissa);
+    EXPECT_EQ(actual_output_exp2, expectedOutputExp2);
+  }
+
+  void clinger_fast_path_fails_test(const UIntType inputMantissa,
+                                    const int32_t inputExp10) {
+    ASSERT_FALSE(internal::clinger_fast_path<T>({inputMantissa, inputExp10})
+                     .has_value());
+  }
+
+  void eisel_lemire_test(const UIntType inputMantissa, const int32_t inputExp10,
+                         const UIntType expectedOutputMantissa,
+                         const uint32_t expectedOutputExp2) {
+    UIntType actual_output_mantissa = 0;
+    uint32_t actual_output_exp2 = 0;
+
+    auto result = internal::eisel_lemire<T>({inputMantissa, inputExp10});
+
+    ASSERT_TRUE(result.has_value());
+
+    actual_output_mantissa = result->mantissa;
+    actual_output_exp2 = result->exponent;
+
+    EXPECT_EQ(actual_output_mantissa, expectedOutputMantissa);
+    EXPECT_EQ(actual_output_exp2, expectedOutputExp2);
+  }
+
+  void simple_decimal_conversion_test(const char *__restrict numStart,
+                                      const UIntType expectedOutputMantissa,
+                                      const uint32_t expectedOutputExp2,
+                                      const int expectedErrno = 0) {
+    UIntType actual_output_mantissa = 0;
+    uint32_t actual_output_exp2 = 0;
+    libc_errno = 0;
+
+    auto result = internal::simple_decimal_conversion<T>(numStart);
+
+    actual_output_mantissa = result.num.mantissa;
+    actual_output_exp2 = result.num.exponent;
+
+    EXPECT_EQ(actual_output_mantissa, expectedOutputMantissa);
+    EXPECT_EQ(actual_output_exp2, expectedOutputExp2);
+    EXPECT_EQ(result.error, expectedErrno);
+  }
+};
+
+} // namespace LIBC_NAMESPACE
diff --git a/libc/test/src/__support/str_to_long_double_test.cpp b/libc/test/src/__support/str_to_long_double_test.cpp
new file mode 100644
index 0000000..6fefc89
--- /dev/null
+++ b/libc/test/src/__support/str_to_long_double_test.cpp
@@ -0,0 +1,88 @@
+#include "str_to_fp_test.h"
+
+namespace LIBC_NAMESPACE {
+
+using LlvmLibcStrToLongDblTest = LlvmLibcStrToFloatTest<long double>;
+
+#if defined(LIBC_LONG_DOUBLE_IS_FLOAT64)
+
+TEST_F(LlvmLibcStrToLongDblTest, EiselLemireFloat64AsLongDouble) {
+  eisel_lemire_test(123, 0, 0x1EC00000000000, 1029);
+}
+
+#elif defined(LIBC_LONG_DOUBLE_IS_X86_FLOAT80)
+
+TEST_F(LlvmLibcStrToLongDblTest, EiselLemireFloat80Simple) {
+  eisel_lemire_test(123, 0, 0xf600000000000000, 16389);
+  eisel_lemire_test(12345678901234568192u, 0, 0xab54a98ceb1f0c00, 16446);
+}
+
+TEST_F(LlvmLibcStrToLongDblTest, EiselLemireFloat80LongerMantissa) {
+  eisel_lemire_test((UInt128(0x1234567812345678) << 64) +
+                        UInt128(0x1234567812345678),
+                    0, 0x91a2b3c091a2b3c1, 16507);
+  eisel_lemire_test((UInt128(0x1234567812345678) << 64) +
+                        UInt128(0x1234567812345678),
+                    300, 0xd97757de56adb65c, 17503);
+  eisel_lemire_test((UInt128(0x1234567812345678) << 64) +
+                        UInt128(0x1234567812345678),
+                    -300, 0xc30feb9a7618457d, 15510);
+}
+
+// These tests check numbers at the edge of the DETAILED_POWERS_OF_TEN table.
+// This doesn't reach very far into the range for long doubles, since it's sized
+// for doubles and their 11 exponent bits, and not for long doubles and their
+// 15 exponent bits. This is a known tradeoff, and was made because a proper
+// long double table would be approximately 16 times longer (specifically the
+// maximum exponent would need to be about 5000, leading to a 10,000 entry
+// table). This would have significant memory and storage costs all the time to
+// speed up a relatively uncommon path.
+TEST_F(LlvmLibcStrToLongDblTest, EiselLemireFloat80TableLimits) {
+  eisel_lemire_test(1, 347, 0xd13eb46469447567, 17535);
+  eisel_lemire_test(1, -348, 0xfa8fd5a0081c0288, 15226);
+}
+
+TEST_F(LlvmLibcStrToLongDblTest, EiselLemireFloat80Fallback) {
+  // This number is halfway between two possible results, and the algorithm
+  // can't determine which is correct.
+  ASSERT_FALSE(internal::eisel_lemire<long double>({12345678901234567890u, 1})
+                   .has_value());
+
+  // These numbers' exponents are out of range for the current powers of ten
+  // table.
+  ASSERT_FALSE(internal::eisel_lemire<long double>({1, 1000}).has_value());
+  ASSERT_FALSE(internal::eisel_lemire<long double>({1, -1000}).has_value());
+}
+
+#else // Quad precision long double
+
+TEST_F(LlvmLibcStrToLongDblTest, EiselLemireFloat128Simple) {
+  eisel_lemire_test(123, 0, (UInt128(0x1ec0000000000) << 64), 16389);
+  eisel_lemire_test(
+      12345678901234568192u, 0,
+      (UInt128(0x156a95319d63e) << 64) + UInt128(0x1800000000000000), 16446);
+}
+
+TEST_F(LlvmLibcStrToLongDblTest, EiselLemireFloat128LongerMantissa) {
+  eisel_lemire_test(
+      (UInt128(0x1234567812345678) << 64) + UInt128(0x1234567812345678), 0,
+      (UInt128(0x1234567812345) << 64) + UInt128(0x6781234567812345), 16507);
+  eisel_lemire_test(
+      (UInt128(0x1234567812345678) << 64) + UInt128(0x1234567812345678), 300,
+      (UInt128(0x1b2eeafbcad5b) << 64) + UInt128(0x6cb8b4451dfcde19), 17503);
+  eisel_lemire_test(
+      (UInt128(0x1234567812345678) << 64) + UInt128(0x1234567812345678), -300,
+      (UInt128(0x1861fd734ec30) << 64) + UInt128(0x8afa7189f0f7595f), 15510);
+}
+
+TEST_F(LlvmLibcStrToLongDblTest, EiselLemireFloat128Fallback) {
+  ASSERT_FALSE(
+      internal::eisel_lemire<long double>(
+          {(UInt128(0x5ce0e9a56015fec5) << 64) + UInt128(0xaadfa328ae39b333),
+           1})
+          .has_value());
+}
+
+#endif
+
+} // namespace LIBC_NAMESPACE