[libc] Implement log10f correctly rounded for all rounding modes.

[lntue]

Summary

Based on RLIBM implementation similar to logf and log2f. Most of the exceptional inputs are the exact powers of 10.

[lntue]

Fix comments.

[sivachandra]

LGTM but please wait for approval from others.

libc/src/math/generic/log10f.cpp

134

Nit: Does it make sense to add a comment telling the reader about the decimal value?

libc/test/src/math/log10f_test.cpp

35

Nit: Can you add a comment telling the reader what these numbers correspond to?

[zimmermann6]

this revision passes all exhaustive tests, for the four rounding modes, great work!

[santoshn]

Looks good to me. Thanks.

[lntue]

Add decimals of exceptional values to comments.

libc/config/linux/aarch64/entrypoints.txt

set(TARGET_LIBM_ENTRYPOINTS
     libc.src.math.lrintf
     libc.src.math.lrintl
     libc.src.math.lround
     libc.src.math.lroundf
     libc.src.math.lroundl
     libc.src.math.ldexp
     libc.src.math.ldexpf
     libc.src.math.ldexpl
+    libc.src.math.log10f
     libc.src.math.log2f
     libc.src.math.logf
     libc.src.math.logb
     libc.src.math.logbf
     libc.src.math.logbl
     libc.src.math.modf
     libc.src.math.modff
     libc.src.math.modfl

libc/config/linux/x86_64/entrypoints.txt

set(TARGET_LIBM_ENTRYPOINTS
     libc.src.math.ldexpf
     libc.src.math.ldexpl
     libc.src.math.llrint
     libc.src.math.llrintf
     libc.src.math.llrintl
     libc.src.math.llround
     libc.src.math.llroundf
     libc.src.math.llroundl
+    libc.src.math.log10f
     libc.src.math.log2f
     libc.src.math.logf
     libc.src.math.logb
     libc.src.math.logbf
     libc.src.math.logbl
     libc.src.math.lrint
     libc.src.math.lrintf
     libc.src.math.lrintl

libc/spec/stdc.td

HeaderSpec Math = HeaderSpec<
           FunctionSpec<"ilogb", RetValSpec<IntType>, [ArgSpec<DoubleType>]>,
           FunctionSpec<"ilogbf", RetValSpec<IntType>, [ArgSpec<FloatType>]>,
           FunctionSpec<"ilogbl", RetValSpec<IntType>, [ArgSpec<LongDoubleType>]>,
 
           FunctionSpec<"ldexp", RetValSpec<DoubleType>, [ArgSpec<DoubleType>, ArgSpec<IntType>]>,
           FunctionSpec<"ldexpf", RetValSpec<FloatType>, [ArgSpec<FloatType>, ArgSpec<IntType>]>,
           FunctionSpec<"ldexpl", RetValSpec<LongDoubleType>, [ArgSpec<LongDoubleType>, ArgSpec<IntType>]>,
 
+          FunctionSpec<"log10f", RetValSpec<FloatType>, [ArgSpec<FloatType>]>,
+
           FunctionSpec<"log2f", RetValSpec<FloatType>, [ArgSpec<FloatType>]>,
 
           FunctionSpec<"logf", RetValSpec<FloatType>, [ArgSpec<FloatType>]>,
 
           FunctionSpec<"logb", RetValSpec<DoubleType>, [ArgSpec<DoubleType>]>,
           FunctionSpec<"logbf", RetValSpec<FloatType>, [ArgSpec<FloatType>]>,
           FunctionSpec<"logbl", RetValSpec<LongDoubleType>, [ArgSpec<LongDoubleType>]>,
 

libc/src/math/CMakeLists.txt

 add_math_entrypoint_object(ilogb)
 add_math_entrypoint_object(ilogbf)
 add_math_entrypoint_object(ilogbl)
 
 add_math_entrypoint_object(ldexp)
 add_math_entrypoint_object(ldexpf)
 add_math_entrypoint_object(ldexpl)
 
+add_math_entrypoint_object(log10f)
+
 add_math_entrypoint_object(log2f)
 
 add_math_entrypoint_object(logf)
 
 add_math_entrypoint_object(logb)
 add_math_entrypoint_object(logbf)
 add_math_entrypoint_object(logbl)
 

libc/src/math/generic/CMakeLists.txt

HDRS
     common_constants.h
   SRCS
     common_constants.cpp
   COMPILE_OPTIONS
     -Wno-c++17-extensions
 )
 
 add_entrypoint_object(
+  log10f
+  SRCS
+    log10f.cpp
+  HDRS
+    ../log10f.h
+  DEPENDS
+    .common_constants
+    libc.src.__support.FPUtil.fputil
+  COMPILE_OPTIONS
+    -O3
+    -Wno-c++17-extensions
+)
+
+add_entrypoint_object(
   log2f
   SRCS
     log2f.cpp
   HDRS
     ../log2f.h
   DEPENDS
     .common_constants
     libc.src.__support.FPUtil.fputil

libc/src/math/generic/log10f.cpp

+//===-- Single-precision log10(x) function --------------------------------===//
+//
+// 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/math/log10f.h"
+#include "common_constants.h" // Lookup table for (1/f)
+#include "src/__support/FPUtil/BasicOperations.h"
+#include "src/__support/FPUtil/FEnvUtils.h"
+#include "src/__support/FPUtil/FMA.h"
+#include "src/__support/FPUtil/FPBits.h"
+#include "src/__support/FPUtil/PolyEval.h"
+#include "src/__support/common.h"
+
+// This is an algorithm for log10(x) in single precision which is
+// correctly rounded for all rounding modes, based on the implementation of
+// log10(x) from the RLIBM project at:
+// https://people.cs.rutgers.edu/~sn349/rlibm
+
+// Step 1 - Range reduction:
+//   For x = 2^m * 1.mant, log(x) = m * log10(2) + log10(1.m)
+//   If x is denormal, we normalize it by multiplying x by 2^23 and subtracting
+//   m by 23.
+
+// Step 2 - Another range reduction:
+//   To compute log(1.mant), let f be the highest 8 bits including the hidden
+// bit, and d be the difference (1.mant - f), i.e. the remaining 16 bits of the
+// mantissa. Then we have the following approximation formula:
+//   log10(1.mant) = log10(f) + log10(1.mant / f)
+//                 = log10(f) + log10(1 + d/f)
+//                 ~ log10(f) + P(d/f)
+// since d/f is sufficiently small.
+//   log10(f) and 1/f are then stored in two 2^7 = 128 entries look-up tables.
+
+// Step 3 - Polynomial approximation:
+//   To compute P(d/f), we use a single degree-5 polynomial in double precision
+// which provides correct rounding for all but few exception values.
+//   For more detail about how this polynomial is obtained, please refer to the
+// papers:
+//   Lim, J. and Nagarakatte, S., "One Polynomial Approximation to Produce
+// Correctly Rounded Results of an Elementary Function for Multiple
+// Representations and Rounding Modes", Proceedings of the 49th ACM SIGPLAN
+// Symposium on Principles of Programming Languages (POPL-2022), Philadelphia,
+// USA, Jan. 16-22, 2022.
+// https://people.cs.rutgers.edu/~sn349/papers/rlibmall-popl-2022.pdf
+//   Aanjaneya, M., Lim, J., and Nagarakatte, S., "RLibm-Prog: Progressive
+// Polynomial Approximations for Fast Correctly Rounded Math Libraries",
+// Dept. of Comp. Sci., Rutgets U., Technical Report DCS-TR-758, Nov. 2021.
+// https://arxiv.org/pdf/2111.12852.pdf.
+
+namespace __llvm_libc {
+
+// Exact power of 10 in float:
+
+// Lookup table for log10(f) = log10(1 + n*2^(-7)) where n = 0..127.
+static constexpr double LOG10_F[128] = {
+    0x0.0000000000000p+0, 0x1.bafd47221ed26p-9, 0x1.b9476a4fcd10fp-8,
+    0x1.49b0851443684p-7, 0x1.b5e908eb13790p-7, 0x1.10a83a8446c78p-6,
+    0x1.45f4f5acb8be0p-6, 0x1.7adc3df3b1ff8p-6, 0x1.af5f92b00e610p-6,
+    0x1.e3806acbd058fp-6, 0x1.0ba01a8170000p-5, 0x1.25502c0fc314cp-5,
+    0x1.3ed1199a5e425p-5, 0x1.58238eeb353dap-5, 0x1.71483427d2a99p-5,
+    0x1.8a3fadeb847f4p-5, 0x1.a30a9d609efeap-5, 0x1.bba9a058dfd84p-5,
+    0x1.d41d5164facb4p-5, 0x1.ec6647eb58808p-5, 0x1.02428c1f08016p-4,
+    0x1.0e3d29d81165ep-4, 0x1.1a23445501816p-4, 0x1.25f5215eb594ap-4,
+    0x1.31b3055c47118p-4, 0x1.3d5d335c53179p-4, 0x1.48f3ed1df48fbp-4,
+    0x1.5477731973e85p-4, 0x1.5fe80488af4fdp-4, 0x1.6b45df6f3e2c9p-4,
+    0x1.769140a2526fdp-4, 0x1.81ca63d05a44ap-4, 0x1.8cf183886480dp-4,
+    0x1.9806d9414a209p-4, 0x1.a30a9d609efeap-4, 0x1.adfd07416be07p-4,
+    0x1.b8de4d3ab3d98p-4, 0x1.c3aea4a5c6effp-4, 0x1.ce6e41e463da5p-4,
+    0x1.d91d5866aa99cp-4, 0x1.e3bc1ab0e19fep-4, 0x1.ee4aba610f204p-4,
+    0x1.f8c9683468191p-4, 0x1.019c2a064b486p-3, 0x1.06cbd67a6c3b6p-3,
+    0x1.0bf3d0937c41cp-3, 0x1.11142f0811357p-3, 0x1.162d082ac9d10p-3,
+    0x1.1b3e71ec94f7bp-3, 0x1.204881dee8777p-3, 0x1.254b4d35e7d3cp-3,
+    0x1.2a46e8ca7ba2ap-3, 0x1.2f3b691c5a001p-3, 0x1.3428e2540096dp-3,
+    0x1.390f6844a0b83p-3, 0x1.3def0e6dfdf85p-3, 0x1.42c7e7fe3fc02p-3,
+    0x1.479a07d3b6411p-3, 0x1.4c65807e93338p-3, 0x1.512a644296c3dp-3,
+    0x1.55e8c518b10f8p-3, 0x1.5aa0b4b0988fap-3, 0x1.5f52447255c92p-3,
+    0x1.63fd857fc49bbp-3, 0x1.68a288b60b7fcp-3, 0x1.6d415eaf0906bp-3,
+    0x1.71da17c2b7e80p-3, 0x1.766cc40889e85p-3, 0x1.7af97358b9e04p-3,
+    0x1.7f80354d952a0p-3, 0x1.84011944bcb75p-3, 0x1.887c2e605e119p-3,
+    0x1.8cf183886480dp-3, 0x1.9161276ba2978p-3, 0x1.95cb2880f45bap-3,
+    0x1.9a2f95085a45cp-3, 0x1.9e8e7b0c0d4bep-3, 0x1.a2e7e8618c2d2p-3,
+    0x1.a73beaaaa22f4p-3, 0x1.ab8a8f56677fcp-3, 0x1.afd3e3a23b680p-3,
+    0x1.b417f49ab8807p-3, 0x1.b856cf1ca3105p-3, 0x1.bc907fd5d1c40p-3,
+    0x1.c0c5134610e26p-3, 0x1.c4f495c0002a2p-3, 0x1.c91f1369eb7cap-3,
+    0x1.cd44983e9e7bdp-3, 0x1.d165300e333f7p-3, 0x1.d580e67edc43dp-3,
+    0x1.d997c70da9b47p-3, 0x1.dda9dd0f4a329p-3, 0x1.e1b733b0c7381p-3,
+    0x1.e5bfd5f83d342p-3, 0x1.e9c3cec58f807p-3, 0x1.edc328d3184afp-3,
+    0x1.f1bdeeb654901p-3, 0x1.f5b42ae08c407p-3, 0x1.f9a5e79f76ac5p-3,
+    0x1.fd932f1ddb4d6p-3, 0x1.00be05b217844p-2, 0x1.02b0432c96ff0p-2,
+    0x1.04a054e139004p-2, 0x1.068e3fa282e3dp-2, 0x1.087a0832fa7acp-2,
+    0x1.0a63b3456c819p-2, 0x1.0c4b457d3193dp-2, 0x1.0e30c36e71a7fp-2,
+    0x1.1014319e661bdp-2, 0x1.11f594839a5bdp-2, 0x1.13d4f0862b2e1p-2,
+    0x1.15b24a0004a92p-2, 0x1.178da53d1ee01p-2, 0x1.1967067bb94b8p-2,
+    0x1.1b3e71ec94f7bp-2, 0x1.1d13ebb32d7f9p-2, 0x1.1ee777e5f0dc3p-2,
+    0x1.20b91a8e76105p-2, 0x1.2288d7a9b2b64p-2, 0x1.2456b3282f786p-2,
+    0x1.2622b0ee3b79dp-2, 0x1.27ecd4d41eb67p-2, 0x1.29b522a64b609p-2,
+    0x1.2b7b9e258e422p-2, 0x1.2d404b073e27ep-2, 0x1.2f032cf56a5bep-2,
+    0x1.30c4478f0835fp-2, 0x1.32839e681fc62p-2};
+
+INLINE_FMA
+LLVM_LIBC_FUNCTION(float, log10f, (float x)) {
+  constexpr double LOG10_2 = 0x1.34413509f79ffp-2;
+
+  using FPBits = typename fputil::FPBits<float>;
+  FPBits xbits(x);
+  double m = 0.0;
+
+  // Exact powers of 10 and other hard-to-round cases.
+  switch (xbits.uintval()) {
+  case 0x4120'0000U: // x = 10
+    return 1.0f;
+  case 0x42c8'0000U: // x = 100
+    return 2.0f;
+  case 0x447a'0000U: // x = 1,000
+    return 3.0f;
+  case 0x461c'4000U: // x = 10,000
+    return 4.0f;
+  case 0x47c3'5000U: // x = 100,000
+    return 5.0f;
+  case 0x4974'2400U: // x = 1,000,000
+    return 6.0f;
+  case 0x4b18'9680U: // x = 10,000,000
+    return 7.0f;
+  case 0x4cbe'bc20U: // x = 100,000,000
+    return 8.0f;
+  case 0x4e6e'6b28U: // x = 1,000,000,000
+    return 9.0f;
+  case 0x5015'02f9U: // x = 10,000,000,000
+    return 10.0f;
+  case 0x4f134f83U:
+    if (fputil::get_round() == FE_UPWARD)
+      return 0x1.2c9314p+3f;
+    break;
+  case 0x7956ba5eU: {
+    int round_mode = fputil::get_round();
+    if (round_mode == FE_DOWNWARD || round_mode == FE_TOWARDZERO)
+      return 0x1.16bebap+5f;
+    break;
+  }
+  }
+
+  if (xbits.uintval() < FPBits::MIN_NORMAL ||
+      xbits.uintval() > FPBits::MAX_NORMAL) {
+    if (xbits.is_zero()) {
+      return static_cast<float>(FPBits::neg_inf());
+    }
+    if (xbits.get_sign() && !xbits.is_nan()) {
+      return FPBits::build_nan(1 << (fputil::MantissaWidth<float>::VALUE - 1));
+    }
+    if (xbits.is_inf_or_nan()) {
+      return x;
+    }
+    // Normalize denormal inputs.
+    xbits.val *= 0x1.0p23f;
+    m -= 23.0;
+  }
+
+  m += static_cast<double>(xbits.get_exponent());
+  // Set bits to 1.m
+  xbits.set_unbiased_exponent(0x7F);
+  int f_index = xbits.get_mantissa() >> 16;
+
+  FPBits f(xbits.val);
+  f.bits &= ~0x0000'FFFF;
+
+  double d = static_cast<float>(xbits) - static_cast<float>(f);
+  d *= ONE_OVER_F[f_index];
+
+  double extra_factor =
+      fputil::fma(static_cast<double>(m), LOG10_2, LOG10_F[f_index]);
+
+  double r = fputil::polyeval(d, extra_factor, 0x1.bcb7b1526e4c5p-2,
+                              -0x1.bcb7b1518a5e9p-3, 0x1.287a72a6f716p-3,
+                              -0x1.bcadb40b85565p-4, 0x1.5e0bc97f97e22p-4);
+
+  return static_cast<float>(r);
+}
+
+} // namespace __llvm_libc

libc/src/math/log10f.h

+//===-- Implementation header for log10f ------------------------*- C++ -*-===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_MATH_LOG10F_H
+#define LLVM_LIBC_SRC_MATH_LOG10F_H
+
+namespace __llvm_libc {
+
+float log10f(float x);
+
+} // namespace __llvm_libc
+
+#endif // LLVM_LIBC_SRC_MATH_LOG10F_H

libc/test/src/math/CMakeLists.txt

add_fp_unittest(
   SRCS
     log2f_test.cpp
   DEPENDS
     libc.include.math
     libc.src.math.log2f
     libc.src.__support.FPUtil.fputil
 )
 
+add_fp_unittest(
+  log10f_test
+  NEED_MPFR
+  SUITE
+    libc_math_unittests
+  SRCS
+    log10f_test.cpp
+  DEPENDS
+    libc.include.math
+    libc.src.math.log10f
+    libc.src.__support.FPUtil.fputil
+)
+
 add_subdirectory(generic)
 add_subdirectory(exhaustive)
 add_subdirectory(differential_testing)

libc/test/src/math/differential_testing/CMakeLists.txt

add_diff_binary(
   DEPENDS
     .single_input_single_output_diff
     libc.src.math.floorf
   COMPILE_OPTIONS
     -fno-builtin
 )
 
 add_diff_binary(
+  log10f_perf
+  SRCS
+    log10f_perf.cpp
+  DEPENDS
+    .single_input_single_output_diff
+    libc.src.math.log10f
+  COMPILE_OPTIONS
+    -fno-builtin
+)
+
+add_diff_binary(
   log2f_diff
   SRCS
     log2f_diff.cpp
   DEPENDS
     .single_input_single_output_diff
     libc.src.math.log2f
   COMPILE_OPTIONS
     -fno-builtin

libc/test/src/math/differential_testing/log10f_perf.cpp

+//===-- Differential test for log10f --------------------------------------===//
+//
+// 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 "SingleInputSingleOutputDiff.h"
+
+#include "src/math/log10f.h"
+
+#include <math.h>
+
+SINGLE_INPUT_SINGLE_OUTPUT_PERF(float, __llvm_libc::log10f, ::log10f,
+                                "log10f_perf.log")

libc/test/src/math/exhaustive/CMakeLists.txt

DEPENDS
     libc.include.math
     libc.src.math.logf
     libc.src.__support.FPUtil.fputil
   LINK_OPTIONS
     -lpthread
 )
 
 add_fp_unittest(
+  log10f_test
+  NO_RUN_POSTBUILD
+  NEED_MPFR
+  SUITE
+    libc_math_exhaustive_tests
+  SRCS
+    log10f_test.cpp
+  DEPENDS
+    .exhaustive_test
+    libc.include.math
+    libc.src.math.log10f
+    libc.src.__support.FPUtil.fputil
+  LINK_OPTIONS
+    -lpthread
+)
+
+add_fp_unittest(
   log2f_test
   NO_RUN_POSTBUILD
   NEED_MPFR
   SUITE
     libc_math_exhaustive_tests
   SRCS
     log2f_test.cpp
   DEPENDS
     .exhaustive_test
     libc.include.math
     libc.src.math.log2f
     libc.src.__support.FPUtil.fputil
   LINK_OPTIONS
     -lpthread
 )

libc/test/src/math/exhaustive/log10f_test.cpp

+//===-- Exhaustive test for log10f ----------------------------------------===//
+//
+// 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 "exhaustive_test.h"
+#include "src/__support/FPUtil/FPBits.h"
+#include "src/math/log10f.h"
+#include "utils/MPFRWrapper/MPFRUtils.h"
+#include "utils/UnitTest/FPMatcher.h"
+
+using FPBits = __llvm_libc::fputil::FPBits<float>;
+
+namespace mpfr = __llvm_libc::testing::mpfr;
+
+struct LlvmLibcLog10fExhaustiveTest : public LlvmLibcExhaustiveTest<uint32_t> {
+  void check(uint32_t start, uint32_t stop,
+             mpfr::RoundingMode rounding) override {
+    mpfr::ForceRoundingMode r(rounding);
+    uint32_t bits = start;
+    do {
+      FPBits xbits(bits);
+      float x = float(xbits);
+      EXPECT_MPFR_MATCH(mpfr::Operation::Log10, x, __llvm_libc::log10f(x), 0.5,
+                        rounding);
+    } while (bits++ < stop);
+  }
+};
+
+// Range: All non-negative;
+static constexpr uint32_t START = 0x0000'0000U;
+static constexpr uint32_t STOP = 0x7f80'0000U;
+// Range: [1, 10];
+// static constexpr uint32_t START = 0x3f80'0000U;
+// static constexpr uint32_t STOP  = 0x41c0'0000U;
+static constexpr int NUM_THREADS = 16;
+
+TEST_F(LlvmLibcLog10fExhaustiveTest, RoundNearestTieToEven) {
+  test_full_range(START, STOP, NUM_THREADS, mpfr::RoundingMode::Nearest);
+}
+
+TEST_F(LlvmLibcLog10fExhaustiveTest, RoundUp) {
+  test_full_range(START, STOP, NUM_THREADS, mpfr::RoundingMode::Upward);
+}
+
+TEST_F(LlvmLibcLog10fExhaustiveTest, RoundDown) {
+  test_full_range(START, STOP, NUM_THREADS, mpfr::RoundingMode::Downward);
+}
+
+TEST_F(LlvmLibcLog10fExhaustiveTest, RoundTowardZero) {
+  test_full_range(START, STOP, NUM_THREADS, mpfr::RoundingMode::TowardZero);
+}

libc/test/src/math/log10f_test.cpp

+//===-- Unittests for log10f ----------------------------------------------===//
+//
+// 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/FPBits.h"
+#include "src/math/log10f.h"
+#include "utils/MPFRWrapper/MPFRUtils.h"
+#include "utils/UnitTest/FPMatcher.h"
+#include "utils/UnitTest/Test.h"
+#include <math.h>
+
+#include <errno.h>
+#include <stdint.h>
+
+namespace mpfr = __llvm_libc::testing::mpfr;
+
+DECLARE_SPECIAL_CONSTANTS(float)
+
+TEST(LlvmLibcLog10fTest, SpecialNumbers) {
+  EXPECT_FP_EQ(aNaN, __llvm_libc::log10f(aNaN));
+  EXPECT_FP_EQ(inf, __llvm_libc::log10f(inf));
+  EXPECT_TRUE(FPBits(__llvm_libc::log10f(neg_inf)).is_nan());
+  EXPECT_FP_EQ(neg_inf, __llvm_libc::log10f(0.0f));
+  EXPECT_FP_EQ(neg_inf, __llvm_libc::log10f(-0.0f));
+  EXPECT_TRUE(FPBits(__llvm_libc::log10f(-1.0f)).is_nan());
+  EXPECT_FP_EQ(zero, __llvm_libc::log10f(1.0f));
+}
+
+TEST(LlvmLibcLog10fTest, TrickyInputs) {
+  constexpr int N = 12;
+  constexpr uint32_t INPUTS[N] = {0x41200000U, 0x42c80000U, 0x447a0000U,
+                                  0x461c4000U, 0x47c35000U, 0x49742400U,
+                                  0x4b189680U, 0x4cbebc20U, 0x4e6e6b28U,
+                                  0x501502f9U, 0x4f134f83U, 0x7956ba5eU};
+
+  for (int i = 0; i < N; ++i) {
+    float x = float(FPBits(INPUTS[i]));
+    EXPECT_MPFR_MATCH_ALL_ROUNDING(mpfr::Operation::Log10, x,
+                                   __llvm_libc::log10f(x), 0.5);
+  }
+}
+
+TEST(LlvmLibcLog10fTest, InFloatRange) {
+  constexpr uint32_t COUNT = 1000000;
+  constexpr uint32_t STEP = UINT32_MAX / COUNT;
+  for (uint32_t i = 0, v = 0; i <= COUNT; ++i, v += STEP) {
+    float x = float(FPBits(v));
+    if (isnan(x) || isinf(x))
+      continue;
+    errno = 0;
+    float result = __llvm_libc::log10f(x);
+    // If the computation resulted in an error or did not produce valid result
+    // in the single-precision floating point range, then ignore comparing with
+    // MPFR result as MPFR can still produce valid results because of its
+    // wider precision.
+    if (isnan(result) || isinf(result) || errno != 0)
+      continue;
+    ASSERT_MPFR_MATCH_ALL_ROUNDING(mpfr::Operation::Log10, x,
+                                   __llvm_libc::log10f(x), 0.5);
+  }
+}

libc/utils/MPFRWrapper/MPFRUtils.h

enum class Operation : int {
   Ceil,
   Cos,
   Exp,
   Exp2,
   Expm1,
   Floor,
   Log,
   Log2,
+  Log10,
   Mod2PI,
   ModPIOver2,
   ModPIOver4,
   Round,
   Sin,
   Sqrt,
   Tan,
   Trunc,

libc/utils/MPFRWrapper/MPFRUtils.cpp

public:
   }
 
   MPFRNumber log2() const {
     MPFRNumber result(*this);
     mpfr_log2(result.value, value, mpfr_rounding);
     return result;
   }
 
+  MPFRNumber log10() const {
+    MPFRNumber result(*this);
+    mpfr_log10(result.value, value, mpfr_rounding);
+    return result;
+  }
+
   MPFRNumber remquo(const MPFRNumber &divisor, int &quotient) {
     MPFRNumber remainder(*this);
     long q;
     mpfr_remquo(remainder.value, &q, value, divisor.value, mpfr_rounding);
     quotient = q;
     return remainder;
   }
 
unary_operation(Operation op, InputType input, unsigned int precision,
   case Operation::Expm1:
     return mpfrInput.expm1();
   case Operation::Floor:
     return mpfrInput.floor();
   case Operation::Log:
     return mpfrInput.log();
   case Operation::Log2:
     return mpfrInput.log2();
+  case Operation::Log10:
+    return mpfrInput.log10();
   case Operation::Mod2PI:
     return mpfrInput.mod_2pi();
   case Operation::ModPIOver2:
     return mpfrInput.mod_pi_over_2();
   case Operation::ModPIOver4:
     return mpfrInput.mod_pi_over_4();
   case Operation::Round:
     return mpfrInput.round();