[libc][math][c23] Add sinf16 C23 math function (#116674)

wldfngrs · overmighty · web-flow · commit cd04653c4e7d · 2024-12-03T21:08:46.000+01:00
Co-authored-by: OverMighty &lt;its.overmighty@gmail.com&gt;
diff --git a/libc/config/linux/x86_64/entrypoints.txt b/libc/config/linux/x86_64/entrypoints.txt
@@ -700,6 +700,7 @@ if(LIBC_TYPES_HAS_FLOAT16)
     libc.src.math.scalbnf16
     libc.src.math.setpayloadf16
     libc.src.math.setpayloadsigf16
+    libc.src.math.sinf16
     libc.src.math.sinhf16
     libc.src.math.sinpif16
     libc.src.math.sqrtf16
diff --git a/libc/docs/math/index.rst b/libc/docs/math/index.rst
@@ -336,7 +336,7 @@ Higher Math Functions
 +-----------+------------------+-----------------+------------------------+----------------------+------------------------+------------------------+----------------------------+
 | rsqrt     |                  |                 |                        |                      |                        | 7.12.7.9               | F.10.4.9                   |
 +-----------+------------------+-----------------+------------------------+----------------------+------------------------+------------------------+----------------------------+
-| sin       | |check|          | |check|         |                        |                      |                        | 7.12.4.6               | F.10.1.6                   |
+| sin       | |check|          | |check|         |                        | |check|              |                        | 7.12.4.6               | F.10.1.6                   |
 +-----------+------------------+-----------------+------------------------+----------------------+------------------------+------------------------+----------------------------+
 | sincos    | |check|          | |check|         |                        |                      |                        |                        |                            |
 +-----------+------------------+-----------------+------------------------+----------------------+------------------------+------------------------+----------------------------+
diff --git a/libc/newhdrgen/yaml/math.yaml b/libc/newhdrgen/yaml/math.yaml
@@ -2339,6 +2339,13 @@ functions:
     return_type: float
     arguments:
       - type: float
+  - name: sinf16
+    standards:
+      - stdc
+    return_type: _Float16
+    arguments:
+      - type: _Float16
+    guard: LIBC_TYPES_HAS_FLOAT16
   - name: sinhf
     standards:
       - stdc
diff --git a/libc/src/math/CMakeLists.txt b/libc/src/math/CMakeLists.txt
@@ -484,6 +484,7 @@ add_math_entrypoint_object(sincosf)
 
 add_math_entrypoint_object(sin)
 add_math_entrypoint_object(sinf)
+add_math_entrypoint_object(sinf16)
 add_math_entrypoint_object(sinpif)
 add_math_entrypoint_object(sinpif16)
 
diff --git a/libc/src/math/generic/CMakeLists.txt b/libc/src/math/generic/CMakeLists.txt
@@ -498,6 +498,27 @@ add_entrypoint_object(
     ${libc_opt_high_flag}
 )
 
+add_entrypoint_object(
+  sinf16
+  SRCS
+    sinf16.cpp
+  HDRS
+    ../sinf16.h
+  DEPENDS
+    .sincosf16_utils
+    libc.hdr.errno_macros
+    libc.hdr.fenv_macros
+    libc.src.__support.FPUtil.cast
+    libc.src.__support.FPUtil.fenv_impl
+    libc.src.__support.FPUtil.fp_bits
+    libc.src.__support.FPUtil.except_value_utils
+    libc.src.__support.FPUtil.multiply_add
+    libc.src.__support.macros.optimization
+    libc.src.__support.macros.properties.types
+  COMPILE_OPTIONS
+    -O3
+)
+
 add_entrypoint_object(
   sincos
   SRCS
diff --git a/libc/src/math/generic/sincosf16_utils.h b/libc/src/math/generic/sincosf16_utils.h
@@ -11,6 +11,7 @@
 
 #include "src/__support/FPUtil/FPBits.h"
 #include "src/__support/FPUtil/PolyEval.h"
+#include "src/__support/FPUtil/cast.h"
 #include "src/__support/FPUtil/nearest_integer.h"
 #include "src/__support/common.h"
 #include "src/__support/macros/config.h"
@@ -46,10 +47,31 @@ LIBC_INLINE int32_t range_reduction_sincospif16(float x, float &y) {
   return static_cast<int32_t>(kf);
 }
 
-LIBC_INLINE void sincospif16_eval(float xf, float &sin_k, float &cos_k,
-                                  float &sin_y, float &cosm1_y) {
-  float y;
-  int32_t k = range_reduction_sincospif16(xf, y);
+// Recall, range reduction:
+//   k = round(x * 32/pi)
+//   y = x * 32/pi - k
+//
+// The constant 0x1.45f306dc9c883p3 is 32/pi rounded to double-precision.
+// 32/pi is generated by Sollya with the following commands:
+// > display = hexadecimal;
+// > round(32/pi, D, RN);
+//
+// The precision choice of 'double' is to minimize rounding errors
+// in this initial scaling step, preserving enough bits so errors accumulated
+// while computing the subtraction: y = x * 32/pi - round(x * 32/pi)
+// are beyond the least-significant bit of single-precision used during
+// further intermediate computation.
+LIBC_INLINE int32_t range_reduction_sincosf16(float x, float &y) {
+  double prod = x * 0x1.45f306dc9c883p3;
+  double kf = fputil::nearest_integer(prod);
+  y = static_cast<float>(prod - kf);
+
+  return static_cast<int32_t>(kf);
+}
+
+static LIBC_INLINE void sincosf16_poly_eval(int32_t k, float y, float &sin_k,
+                                            float &cos_k, float &sin_y,
+                                            float &cosm1_y) {
 
   sin_k = SIN_K_PI_OVER_32[k & 63];
   cos_k = SIN_K_PI_OVER_32[(k + 16) & 63];
@@ -72,6 +94,22 @@ LIBC_INLINE void sincospif16_eval(float xf, float &sin_k, float &cos_k,
                                    0x1.a6f7a2p-29f);
 }
 
+LIBC_INLINE void sincosf16_eval(float xf, float &sin_k, float &cos_k,
+                                float &sin_y, float &cosm1_y) {
+  float y;
+  int32_t k = range_reduction_sincosf16(xf, y);
+
+  sincosf16_poly_eval(k, y, sin_k, cos_k, sin_y, cosm1_y);
+}
+
+LIBC_INLINE void sincospif16_eval(float xf, float &sin_k, float &cos_k,
+                                  float &sin_y, float &cosm1_y) {
+  float y;
+  int32_t k = range_reduction_sincospif16(xf, y);
+
+  sincosf16_poly_eval(k, y, sin_k, cos_k, sin_y, cosm1_y);
+}
+
 } // namespace LIBC_NAMESPACE_DECL
 
 #endif // LLVM_LIBC_SRC_MATH_GENERIC_SINCOSF16_UTILS_H
diff --git a/libc/src/math/generic/sinf16.cpp b/libc/src/math/generic/sinf16.cpp
@@ -0,0 +1,108 @@
+//===-- Half-precision sin(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/sinf16.h"
+#include "hdr/errno_macros.h"
+#include "hdr/fenv_macros.h"
+#include "sincosf16_utils.h"
+#include "src/__support/FPUtil/FEnvImpl.h"
+#include "src/__support/FPUtil/FPBits.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/macros/optimization.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+constexpr size_t N_EXCEPTS = 4;
+
+constexpr fputil::ExceptValues<float16, N_EXCEPTS> SINF16_EXCEPTS{{
+    // (input, RZ output, RU offset, RD offset, RN offset)
+    {0x2b45, 0x2b43, 1, 0, 1},
+    {0x585c, 0x3ba3, 1, 0, 1},
+    {0x5cb0, 0xbbff, 0, 1, 0},
+    {0x51f5, 0xb80f, 0, 1, 0},
+}};
+
+LLVM_LIBC_FUNCTION(float16, sinf16, (float16 x)) {
+  using FPBits = fputil::FPBits<float16>;
+  FPBits xbits(x);
+
+  uint16_t x_u = xbits.uintval();
+  uint16_t x_abs = x_u & 0x7fff;
+  float xf = x;
+
+  // Range reduction:
+  // For |x| > pi/32, we perform range reduction as follows:
+  // Find k and y such that:
+  //   x = (k + y) * pi/32
+  //   k is an integer, |y| < 0.5
+  //
+  // This is done by performing:
+  //   k = round(x * 32/pi)
+  //   y = x * 32/pi - k
+  //
+  // Once k and y are computed, we then deduce the answer by the sine of sum
+  // formula:
+  //   sin(x) = sin((k + y) * pi/32)
+  //   	      = sin(k * pi/32) * cos(y * pi/32) +
+  //   	        sin(y * pi/32) * cos(k * pi/32)
+
+  // Handle exceptional values
+  if (LIBC_UNLIKELY(x_abs == 0x585c || x_abs == 0x5cb0 || x_abs == 0x51f5 ||
+                    x_abs == 0x2b45)) {
+    bool x_sign = x_u >> 15;
+    if (auto r = SINF16_EXCEPTS.lookup_odd(x_abs, x_sign);
+        LIBC_UNLIKELY(r.has_value()))
+      return r.value();
+  }
+
+  int rounding = fputil::quick_get_round();
+
+  // Exhaustive tests show that for |x| <= 0x1.f4p-11, 1ULP rounding errors
+  // occur. To fix this, the following apply:
+  if (LIBC_UNLIKELY(x_abs <= 0x13d0)) {
+    // sin(+/-0) = +/-0
+    if (LIBC_UNLIKELY(x_abs == 0U))
+      return x;
+
+    // When x > 0, and rounding upward, sin(x) == x.
+    // When x < 0, and rounding downward, sin(x) == x.
+    if ((rounding == FE_UPWARD && xbits.is_pos()) ||
+        (rounding == FE_DOWNWARD && xbits.is_neg()))
+      return x;
+
+    // When x < 0, and rounding upward, sin(x) == (x - 1ULP)
+    if (rounding == FE_UPWARD && xbits.is_neg()) {
+      x_u--;
+      return FPBits(x_u).get_val();
+    }
+  }
+
+  if (xbits.is_inf_or_nan()) {
+    if (xbits.is_inf()) {
+      fputil::set_errno_if_required(EDOM);
+      fputil::raise_except_if_required(FE_INVALID);
+    }
+
+    return x + FPBits::quiet_nan().get_val();
+  }
+
+  float sin_k, cos_k, sin_y, cosm1_y;
+  sincosf16_eval(xf, sin_k, cos_k, sin_y, cosm1_y);
+
+  if (LIBC_UNLIKELY(sin_y == 0 && sin_k == 0))
+    return FPBits::zero(xbits.sign()).get_val();
+
+  // Since, cosm1_y = cos_y - 1, therfore:
+  //    sin(x) = cos_k * sin_y + sin_k + (cosm1_y * sin_k)
+  return fputil::cast<float16>(fputil::multiply_add(
+      sin_y, cos_k, fputil::multiply_add(cosm1_y, sin_k, sin_k)));
+}
+
+} // namespace LIBC_NAMESPACE_DECL
diff --git a/libc/src/math/generic/tanpif16.cpp b/libc/src/math/generic/tanpif16.cpp
@@ -21,7 +21,7 @@ namespace LIBC_NAMESPACE_DECL {
 
 constexpr size_t N_EXCEPTS = 21;
 
-constexpr fputil::ExceptValues<float16, N_EXCEPTS> TANF16_EXCEPTS{{
+constexpr fputil::ExceptValues<float16, N_EXCEPTS> TANPIF16_EXCEPTS{{
     // (input, RZ output, RU offset, RD offset, RN offset)
     {0x07f2, 0x0e3d, 1, 0, 0}, {0x086a, 0x0eee, 1, 0, 1},
     {0x08db, 0x0fa0, 1, 0, 0}, {0x094c, 0x1029, 1, 0, 0},
@@ -49,7 +49,7 @@ LLVM_LIBC_FUNCTION(float16, tanpif16, (float16 x)) {
       return x;
 
     bool x_sign = x_u >> 15;
-    if (auto r = TANF16_EXCEPTS.lookup_odd(x_abs, x_sign);
+    if (auto r = TANPIF16_EXCEPTS.lookup_odd(x_abs, x_sign);
         LIBC_UNLIKELY(r.has_value()))
       return r.value();
   }
diff --git a/libc/src/math/sinf16.h b/libc/src/math/sinf16.h
@@ -0,0 +1,21 @@
+//===-- Implementation header for sinf16 ------------------------*- 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_SINF16_H
+#define LLVM_LIBC_SRC_MATH_SINF16_H
+
+#include "src/__support/macros/config.h"
+#include "src/__support/macros/properties/types.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+float16 sinf16(float16 x);
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC_MATH_SINF16_H
diff --git a/libc/test/src/math/CMakeLists.txt b/libc/test/src/math/CMakeLists.txt
@@ -85,6 +85,17 @@ add_fp_unittest(
     libc.src.__support.FPUtil.fp_bits
 )
 
+add_fp_unittest(
+  sinf16_test
+  NEED_MPFR
+  SUITE
+    libc-math-unittests
+  SRCS
+    sinf16_test.cpp
+  DEPENDS
+    libc.src.math.sinf16  
+)
+
 add_fp_unittest(
   sinpif_test
   NEED_MPFR
diff --git a/libc/test/src/math/sinf16_test.cpp b/libc/test/src/math/sinf16_test.cpp
@@ -0,0 +1,40 @@
+//===-- Exhaustive test for sinf16 ----------------------------------------===//
+//
+// 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/sinf16.h"
+#include "test/UnitTest/FPMatcher.h"
+#include "test/UnitTest/Test.h"
+#include "utils/MPFRWrapper/MPFRUtils.h"
+
+using LlvmLibcSinf16Test = LIBC_NAMESPACE::testing::FPTest<float16>;
+
+namespace mpfr = LIBC_NAMESPACE::testing::mpfr;
+
+// Range: [0, Inf]
+static constexpr uint16_t POS_START = 0x0000U;
+static constexpr uint16_t POS_STOP = 0x7c00U;
+
+// Range: [-Inf, 0]
+static constexpr uint16_t NEG_START = 0x8000U;
+static constexpr uint16_t NEG_STOP = 0xfc00U;
+
+TEST_F(LlvmLibcSinf16Test, PositiveRange) {
+  for (uint16_t v = POS_START; v <= POS_STOP; ++v) {
+    float16 x = FPBits(v).get_val();
+    EXPECT_MPFR_MATCH_ALL_ROUNDING(mpfr::Operation::Sin, x,
+                                   LIBC_NAMESPACE::sinf16(x), 0.5);
+  }
+}
+
+TEST_F(LlvmLibcSinf16Test, NegativeRange) {
+  for (uint16_t v = NEG_START; v <= NEG_STOP; ++v) {
+    float16 x = FPBits(v).get_val();
+    EXPECT_MPFR_MATCH_ALL_ROUNDING(mpfr::Operation::Sin, x,
+                                   LIBC_NAMESPACE::sinf16(x), 0.5);
+  }
+}
diff --git a/libc/test/src/math/smoke/CMakeLists.txt b/libc/test/src/math/smoke/CMakeLists.txt
@@ -49,6 +49,17 @@ add_fp_unittest(
     libc.src.__support.FPUtil.fp_bits
 )
 
+add_fp_unittest(
+  sinf16_test
+  SUITE
+    libc-math-smoke-tests
+  SRCS
+    sinf16_test.cpp
+  DEPENDS
+    libc.src.errno.errno
+    libc.src.math.sinf16
+)
+
 add_fp_unittest(
   sinpif_test
   SUITE
diff --git a/libc/test/src/math/smoke/sinf16_test.cpp b/libc/test/src/math/smoke/sinf16_test.cpp
@@ -0,0 +1,33 @@
+//===-- Unittests for sinf16 ----------------------------------------------===//
+//
+// 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/errno/libc_errno.h"
+#include "src/math/sinf16.h"
+#include "test/UnitTest/FPMatcher.h"
+#include "test/UnitTest/Test.h"
+
+using LlvmLibcSinf16Test = LIBC_NAMESPACE::testing::FPTest<float16>;
+
+TEST_F(LlvmLibcSinf16Test, SpecialNumbers) {
+  LIBC_NAMESPACE::libc_errno = 0;
+
+  EXPECT_FP_EQ(aNaN, LIBC_NAMESPACE::sinf16(aNaN));
+  EXPECT_MATH_ERRNO(0);
+
+  EXPECT_FP_EQ(zero, LIBC_NAMESPACE::sinf16(zero));
+  EXPECT_MATH_ERRNO(0);
+
+  EXPECT_FP_EQ(neg_zero, LIBC_NAMESPACE::sinf16(neg_zero));
+  EXPECT_MATH_ERRNO(0);
+
+  EXPECT_FP_EQ(aNaN, LIBC_NAMESPACE::sinf16(inf));
+  EXPECT_MATH_ERRNO(EDOM);
+
+  EXPECT_FP_EQ(aNaN, LIBC_NAMESPACE::sinf16(neg_inf));
+  EXPECT_MATH_ERRNO(EDOM);
+}
