[libc][math][c23] Add log10p1f16 C23 math function (llvm#184739)

shikharish · web-flow · commit a7d1a87b30ce · 2026-03-13T09:59:26.000-04:00
Closes llvm#133202 --------- Signed-off-by: Shikhar Soni <shikharish05@gmail.com>
diff --git a/libc/config/baremetal/aarch64/entrypoints.txt b/libc/config/baremetal/aarch64/entrypoints.txt
@@ -650,6 +650,7 @@ if(LIBC_TYPES_HAS_FLOAT16)
     libc.src.math.llrintf16
     libc.src.math.llroundf16
     libc.src.math.log10f16
+    libc.src.math.log10p1f16
     libc.src.math.log2f16
     libc.src.math.logbf16
     libc.src.math.logf16
diff --git a/libc/config/baremetal/arm/entrypoints.txt b/libc/config/baremetal/arm/entrypoints.txt
@@ -661,6 +661,7 @@ if(LIBC_TYPES_HAS_FLOAT16)
     libc.src.math.llrintf16
     libc.src.math.llroundf16
     libc.src.math.log10f16
+    libc.src.math.log10p1f16
     libc.src.math.log2f16
     libc.src.math.logbf16
     libc.src.math.logf16
diff --git a/libc/config/baremetal/riscv/entrypoints.txt b/libc/config/baremetal/riscv/entrypoints.txt
@@ -656,6 +656,7 @@ if(LIBC_TYPES_HAS_FLOAT16)
     libc.src.math.llrintf16
     libc.src.math.llroundf16
     libc.src.math.log10f16
+    libc.src.math.log10p1f16
     libc.src.math.log2f16
     libc.src.math.logbf16
     libc.src.math.logf16
diff --git a/libc/config/darwin/aarch64/entrypoints.txt b/libc/config/darwin/aarch64/entrypoints.txt
@@ -472,6 +472,7 @@ if(LIBC_TYPES_HAS_FLOAT16)
     libc.src.math.llrintf16
     libc.src.math.llroundf16
     libc.src.math.log10f16
+    libc.src.math.log10p1f16
     libc.src.math.log2f16
     libc.src.math.logbf16
     libc.src.math.logf16
diff --git a/libc/config/gpu/amdgpu/entrypoints.txt b/libc/config/gpu/amdgpu/entrypoints.txt
@@ -582,6 +582,7 @@ if(LIBC_TYPES_HAS_FLOAT16)
     libc.src.math.llrintf16
     libc.src.math.llroundf16
     libc.src.math.log10f16
+    libc.src.math.log10p1f16
     libc.src.math.log2f16
     libc.src.math.logbf16
     libc.src.math.logf16
diff --git a/libc/config/gpu/nvptx/entrypoints.txt b/libc/config/gpu/nvptx/entrypoints.txt
@@ -584,6 +584,7 @@ if(LIBC_TYPES_HAS_FLOAT16)
     libc.src.math.llrintf16
     libc.src.math.llroundf16
     libc.src.math.log10f16
+    libc.src.math.log10p1f16
     libc.src.math.log2f16
     libc.src.math.logbf16
     libc.src.math.logf16
diff --git a/libc/config/linux/aarch64/entrypoints.txt b/libc/config/linux/aarch64/entrypoints.txt
@@ -731,6 +731,7 @@ if(LIBC_TYPES_HAS_FLOAT16)
     libc.src.math.llogbf16
     libc.src.math.llrintf16
     libc.src.math.llroundf16
+    libc.src.math.log10p1f16
     libc.src.math.logbf16
     libc.src.math.lrintf16
     libc.src.math.lroundf16
diff --git a/libc/config/linux/riscv/entrypoints.txt b/libc/config/linux/riscv/entrypoints.txt
@@ -747,6 +747,7 @@ if(LIBC_TYPES_HAS_FLOAT16)
     libc.src.math.llrintf16
     libc.src.math.llroundf16
     libc.src.math.log10f16
+    libc.src.math.log10p1f16
     libc.src.math.log2f16
     libc.src.math.logbf16
     libc.src.math.logf16
diff --git a/libc/config/linux/x86_64/entrypoints.txt b/libc/config/linux/x86_64/entrypoints.txt
@@ -797,6 +797,7 @@ if(LIBC_TYPES_HAS_FLOAT16)
     libc.src.math.llrintf16
     libc.src.math.llroundf16
     libc.src.math.log10f16
+    libc.src.math.log10p1f16
     libc.src.math.log2f16
     libc.src.math.logbf16
     libc.src.math.logf16
diff --git a/libc/docs/headers/math/index.rst b/libc/docs/headers/math/index.rst
@@ -323,7 +323,7 @@ Higher Math Functions
 +-----------+------------------+-----------------+------------------------+----------------------+------------------------+------------------------+------------------------+----------------------------+
 | log10     | |check|          | |check|         |                        | |check|              |                        |                        | 7.12.6.12              | F.10.3.12                  |
 +-----------+------------------+-----------------+------------------------+----------------------+------------------------+------------------------+------------------------+----------------------------+
-| log10p1   |                  |                 |                        |                      |                        |                        | 7.12.6.13              | F.10.3.13                  |
+| log10p1   |                  |                 |                        | |check|              |                        |                        | 7.12.6.13              | F.10.3.13                  |
 +-----------+------------------+-----------------+------------------------+----------------------+------------------------+------------------------+------------------------+----------------------------+
 | log1p     | |check|          | |check|         |                        |                      |                        |                        | 7.12.6.14              | F.10.3.14                  |
 +-----------+------------------+-----------------+------------------------+----------------------+------------------------+------------------------+------------------------+----------------------------+
diff --git a/libc/include/math.yaml b/libc/include/math.yaml
@@ -1777,6 +1777,13 @@ functions:
     arguments:
       - type: _Float16
     guard: LIBC_TYPES_HAS_FLOAT16
+  - name: log10p1f16
+    standards:
+      - stdc
+    return_type: _Float16
+    arguments:
+      - type: _Float16
+    guard: LIBC_TYPES_HAS_FLOAT16
   - name: log1p
     standards:
       - stdc
diff --git a/libc/src/__support/math/CMakeLists.txt b/libc/src/__support/math/CMakeLists.txt
@@ -2597,6 +2597,25 @@ add_header_library(
     libc.src.__support.macros.properties.cpu_features
 )
 
+add_header_library(
+  log10p1f16
+  HDRS
+    log10p1f16.h
+  DEPENDS
+    .exp10_float16_constants
+    .expxf16_utils
+    libc.hdr.errno_macros
+    libc.hdr.fenv_macros
+    libc.src.__support.FPUtil.cast
+    libc.src.__support.FPUtil.except_value_utils
+    libc.src.__support.FPUtil.fenv_impl
+    libc.src.__support.FPUtil.fp_bits
+    libc.src.__support.FPUtil.multiply_add
+    libc.src.__support.FPUtil.polyeval
+    libc.src.__support.macros.optimization
+    libc.src.__support.macros.properties.cpu_features
+)
+
 add_header_library(
   log10f
   HDRS
diff --git a/libc/src/__support/math/log10p1f16.h b/libc/src/__support/math/log10p1f16.h
@@ -0,0 +1,207 @@
+//===-- Implementation header for log10p1f16 --------------------*- 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___SUPPORT_MATH_LOG10P1F16_H
+#define LLVM_LIBC_SRC___SUPPORT_MATH_LOG10P1F16_H
+
+#include "include/llvm-libc-macros/float16-macros.h"
+
+#ifdef LIBC_TYPES_HAS_FLOAT16
+
+#include "exp10_float16_constants.h"
+#include "expxf16_utils.h"
+#include "hdr/errno_macros.h"
+#include "hdr/fenv_macros.h"
+#include "src/__support/FPUtil/FEnvImpl.h"
+#include "src/__support/FPUtil/FPBits.h"
+#include "src/__support/FPUtil/PolyEval.h"
+#include "src/__support/FPUtil/cast.h"
+#include "src/__support/FPUtil/except_value_utils.h"
+#include "src/__support/FPUtil/multiply_add.h"
+#include "src/__support/common.h"
+#include "src/__support/macros/config.h"
+#include "src/__support/macros/optimization.h"
+#include "src/__support/macros/properties/cpu_features.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+namespace math {
+
+LIBC_INLINE float16 log10p1f16(float16 x) {
+  using namespace math::expxf16_internal;
+  using FPBits = fputil::FPBits<float16>;
+  FPBits x_bits(x);
+
+  uint16_t x_u = x_bits.uintval();
+  uint16_t x_abs = x_u & 0x7fffU;
+
+  // If x is +-0, NaN, +/-inf, or |x| <= 2^-3.
+  if (LIBC_UNLIKELY(x_abs <= 0x3000U || x_abs >= 0x7c00U)) {
+    // log10p1(NaN) = NaN
+    if (x_bits.is_nan()) {
+      if (x_bits.is_signaling_nan()) {
+        fputil::raise_except_if_required(FE_INVALID);
+        return FPBits::quiet_nan().get_val();
+      }
+
+      return x;
+    }
+
+    // log10p1(+/-0) = +/-0
+    if (x_abs == 0U)
+      return x;
+
+    // log10p1(+inf) = +inf
+    if (x_u == 0x7c00U)
+      return FPBits::inf().get_val();
+
+    // log10p1(-inf) = NaN
+    if (x_abs >= 0x7c00U) {
+      fputil::set_errno_if_required(EDOM);
+      fputil::raise_except_if_required(FE_INVALID);
+      return FPBits::quiet_nan().get_val();
+    }
+
+    // When |x| <= 2^-3, use a degree-5 minimax polynomial on x.
+    // For y = 1+x near 1, the table-based range reduction suffers from
+    // catastrophic cancellation (m*log10(2) + log10(f) nearly cancel).
+    // Computing log10(1+x) directly via polynomial avoids this.
+    //
+    // Generated by Sollya with:
+    //   > display = hexadecimal;
+    //   > Q = fpminimax(log10(1 + x), [|1, 2, 3, 4, 5|], [|SG...|],
+    //                   [-2^-3, 2^-3]);
+    //   > Q;
+    if (x_abs <= 0x3000U) {
+#ifndef LIBC_MATH_HAS_SKIP_ACCURATE_PASS
+      // ExceptValues for the small-|x| polynomial path (|x| <= 2^-3).
+      constexpr size_t N_LOG10P1F16_EXCEPTS = 7;
+      constexpr fputil::ExceptValues<float16, N_LOG10P1F16_EXCEPTS>
+          LOG10P1F16_EXCEPTS = {{
+              // (input, RZ output, RU offset, RD offset, RN offset)
+              // x = 0x1.ep-13
+              {0x0B80U, 0x0683U, 1U, 0U, 0U},
+              // x = 0x1.4fp-6
+              {0x213CU, 0x1C85U, 1U, 0U, 1U},
+              // x = 0x1.82cp-4
+              {0x2E0BU, 0x2904U, 1U, 0U, 0U},
+              // x = 0x1.d24p-4
+              {0x2EC9U, 0x299AU, 1U, 0U, 0U},
+              // x = -0x1.b8p-13
+              {0x89DCU, 0x8516U, 0U, 1U, 1U},
+              // x = -0x1.49p-6
+              {0x9924U, 0x9478U, 0U, 1U, 1U},
+              // x = -0x1.42p-8
+              {0x9D08U, 0x9861U, 0U, 1U, 0U},
+          }};
+
+      if (auto r = LOG10P1F16_EXCEPTS.lookup(x_u); LIBC_UNLIKELY(r.has_value()))
+        return r.value();
+#endif // !LIBC_MATH_HAS_SKIP_ACCURATE_PASS
+
+      float xf = x;
+      return fputil::cast<float16>(
+          xf * fputil::polyeval(xf, 0x1.bcb7b2p-2f, -0x1.bcb4cp-3f,
+                                0x1.2875bcp-3f, -0x1.c2946ep-4f,
+                                0x1.69da2p-4f));
+    }
+  }
+
+  // log10p1(-1) = -inf
+  if (LIBC_UNLIKELY(x_u == 0xbc00U)) {
+    fputil::raise_except_if_required(FE_DIVBYZERO);
+    return FPBits::inf(Sign::NEG).get_val();
+  }
+
+  // log10p1(x) = NaN for x < -1
+  if (LIBC_UNLIKELY(x_u > 0xbc00U)) {
+    fputil::set_errno_if_required(EDOM);
+    fputil::raise_except_if_required(FE_INVALID);
+    return FPBits::quiet_nan().get_val();
+  }
+
+#ifndef LIBC_MATH_HAS_SKIP_ACCURATE_PASS
+  // ExceptValues for the large-|x| table-based path (|x| > 2^-3).
+  constexpr size_t N_LOG10P1F16_EXCEPTS_HI = 12;
+  constexpr fputil::ExceptValues<float16, N_LOG10P1F16_EXCEPTS_HI>
+      LOG10P1F16_EXCEPTS_HI = {{
+          // (input, RZ output, RU offset, RD offset, RN offset)
+          // x = 0x1.3bp-3
+          {0x30ECU, 0x2BF3U, 1U, 0U, 1U},
+          // x = 0x1.ba0p-3
+          {0x32E8U, 0x2D6EU, 1U, 0U, 1U},
+          // x = 0x1.4c4p-2
+          {0x3531U, 0x2FCFU, 1U, 0U, 0U},
+          // x = 0x1.744p+0
+          {0x3DD1U, 0x363CU, 1U, 0U, 1U},
+          // x = 0x1.7d8p+0
+          {0x3DF6U, 0x3656U, 1U, 0U, 1U},
+          // x = 0x1.2p+3
+          {0x4880U, 0x3C00U, 0U, 0U, 0U},
+          // x = 0x1.8cp+6
+          {0x5630U, 0x4000U, 0U, 0U, 0U},
+          // x = 0x1.f44p+6
+          {0x57D1U, 0x4033U, 1U, 0U, 0U},
+          // x = 0x1.f38p+9
+          {0x63CEU, 0x4200U, 0U, 0U, 0U},
+          // x = -0x1.558p-3
+          {0xB156U, 0xAD12U, 0U, 1U, 0U},
+          // x = -0x1.8d8p-2
+          {0xB636U, 0xB2D3U, 0U, 1U, 1U},
+          // x = -0x1.808p-1
+          {0xBA02U, 0xB8D4U, 0U, 1U, 1U},
+      }};
+
+  if (auto r = LOG10P1F16_EXCEPTS_HI.lookup(x_u); LIBC_UNLIKELY(r.has_value()))
+    return r.value();
+#endif // !LIBC_MATH_HAS_SKIP_ACCURATE_PASS
+
+  // For the range reduction, we compute y = 1 + x in float. For |x| > 2^-3,
+  // the addition 1.0f + xf is exact in float, and the result y is bounded away
+  // from 1.0, avoiding catastrophic cancellation in the table decomposition.
+  float xf = x;
+  float y = 1.0f + xf;
+
+  using FPBitsFloat = fputil::FPBits<float>;
+  FPBitsFloat y_bits(y);
+
+  // When y is subnormal or zero, which shouldn't happen since y = 1 + x and
+  // x >= -1 + eps in f16, so y >= eps > 0. But handle y = 0 just in case.
+  if (LIBC_UNLIKELY(y_bits.is_zero()))
+    return FPBits::inf(Sign::NEG).get_val();
+
+  int m = y_bits.get_exponent();
+  // Set y_bits to 1.mant (biased exponent = 127).
+  y_bits.set_biased_exponent(FPBitsFloat::EXP_BIAS);
+  float mant_f = y_bits.get_val();
+
+  // Leading 23 - 5 = 18, so top 5 mantissa bits give index f in [0, 31].
+  int f = y_bits.get_mantissa() >> (FPBitsFloat::FRACTION_LEN - 5);
+
+  // v = 1.mant * 1/f - 1 = d/f
+  float v = fputil::multiply_add(mant_f, ONE_OVER_F_F[f], -1.0f);
+
+  // Degree-3 minimax polynomial generated by Sollya with the following
+  // commands:
+  //   > display = hexadecimal;
+  //   > P = fpminimax(log10(1 + x)/x, 2, [|SG...|], [-2^-5, 2^-5]);
+  //   > x * P;
+  float log10p1_d_over_f =
+      v * fputil::polyeval(v, 0x1.bcb7bp-2f, -0x1.bce168p-3f, 0x1.28acb8p-3f);
+  // log10(1.mant) = log10(f) + log10(1 + d/f)
+  float log10_1_mant = LOG10F_F[f] + log10p1_d_over_f;
+  return fputil::cast<float16>(
+      fputil::multiply_add(static_cast<float>(m), LOG10F_2, log10_1_mant));
+}
+
+} // namespace math
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LIBC_TYPES_HAS_FLOAT16
+
+#endif // LLVM_LIBC_SRC___SUPPORT_MATH_LOG10P1F16_H
diff --git a/libc/src/math/CMakeLists.txt b/libc/src/math/CMakeLists.txt
@@ -385,6 +385,7 @@ add_math_entrypoint_object(ldexpbf16)
 add_math_entrypoint_object(log10)
 add_math_entrypoint_object(log10f)
 add_math_entrypoint_object(log10f16)
+add_math_entrypoint_object(log10p1f16)
 
 add_math_entrypoint_object(log1p)
 add_math_entrypoint_object(log1pf)
diff --git a/libc/src/math/generic/CMakeLists.txt b/libc/src/math/generic/CMakeLists.txt
@@ -1837,6 +1837,17 @@ add_entrypoint_object(
     libc.src.errno.errno
 )
 
+add_entrypoint_object(
+  log10p1f16
+  SRCS
+    log10p1f16.cpp
+  HDRS
+    ../log10p1f16.h
+  DEPENDS
+    libc.src.__support.math.log10p1f16
+    libc.src.errno.errno
+)
+
 add_entrypoint_object(
   log1p
   SRCS
diff --git a/libc/src/math/generic/log10p1f16.cpp b/libc/src/math/generic/log10p1f16.cpp
@@ -0,0 +1,18 @@
+//===-- Half-precision log10(1+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/log10p1f16.h"
+#include "src/__support/math/log10p1f16.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+LLVM_LIBC_FUNCTION(float16, log10p1f16, (float16 x)) {
+  return math::log10p1f16(x);
+}
+
+} // namespace LIBC_NAMESPACE_DECL
diff --git a/libc/src/math/log10p1f16.h b/libc/src/math/log10p1f16.h
@@ -0,0 +1,21 @@
+//===-- Implementation header for log10p1f16 --------------------*- 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_LOG10P1F16_H
+#define LLVM_LIBC_SRC_MATH_LOG10P1F16_H
+
+#include "src/__support/macros/config.h"
+#include "src/__support/macros/properties/types.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+float16 log10p1f16(float16 x);
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC_MATH_LOG10P1F16_H
diff --git a/libc/test/src/math/CMakeLists.txt b/libc/test/src/math/CMakeLists.txt
diff --git a/libc/test/src/math/log10p1f16_test.cpp b/libc/test/src/math/log10p1f16_test.cpp
diff --git a/libc/test/src/math/smoke/CMakeLists.txt b/libc/test/src/math/smoke/CMakeLists.txt
diff --git a/libc/test/src/math/smoke/log10p1f16_test.cpp b/libc/test/src/math/smoke/log10p1f16_test.cpp
diff --git a/libc/utils/MPFRWrapper/MPCommon.cpp b/libc/utils/MPFRWrapper/MPCommon.cpp
diff --git a/libc/utils/MPFRWrapper/MPCommon.h b/libc/utils/MPFRWrapper/MPCommon.h
diff --git a/libc/utils/MPFRWrapper/MPFRUtils.cpp b/libc/utils/MPFRWrapper/MPFRUtils.cpp
diff --git a/libc/utils/MPFRWrapper/MPFRUtils.h b/libc/utils/MPFRWrapper/MPFRUtils.h
