[libc][math][c23] Refactor expf16 (#101373)

Also updates and sorts CMake target dependencies, and corrects the smoke
test that expected expf16(sNaN) to return sNaN instead of aNaN, although
the test still passed, as FPMatcher only checks whether both sides are
NaN, not whether they're the same NaN value.

Author: overmighty

libc/src/math/generic/CMakeLists.txt

@@ -1236,11 +1236,12 @@ add_entrypoint_object(
     libc.hdr.errno_macros
     libc.hdr.fenv_macros
     libc.src.__support.CPP.array
+    libc.src.__support.FPUtil.except_value_utils
     libc.src.__support.FPUtil.fenv_impl
     libc.src.__support.FPUtil.fp_bits
-    libc.src.__support.FPUtil.polyeval
     libc.src.__support.FPUtil.multiply_add
     libc.src.__support.FPUtil.nearest_integer
+    libc.src.__support.FPUtil.polyeval
     libc.src.__support.FPUtil.rounding_mode
     libc.src.__support.macros.optimization
   COMPILE_OPTIONS

libc/src/math/generic/expf16.cpp

@@ -127,9 +127,8 @@ LLVM_LIBC_FUNCTION(float16, expf16, (float16 x)) {
       //   > display = hexadecimal;
       //   > P = fpminimax(expm1(x)/x, 2, [|SG...|], [-2^-5, 2^-5]);
       //   > 1 + x * P;
-      float r =
-          fputil::polyeval(xf, 0x1p+0f, 0x1p+0f, 0x1.0004p-1f, 0x1.555778p-3f);
-      return static_cast<float16>(r);
+      return static_cast<float16>(
+          fputil::polyeval(xf, 0x1p+0f, 0x1p+0f, 0x1.0004p-1f, 0x1.555778p-3f));
     }
   }
 
@@ -150,7 +149,7 @@ LLVM_LIBC_FUNCTION(float16, expf16, (float16 x)) {
   // respectively.  exp(lo) is computed using a degree-3 minimax polynomial
   // generated by Sollya.
 
-  float xf = static_cast<float>(x);
+  float xf = x;
   float kf = fputil::nearest_integer(xf * 0x1.0p+3f);
   int x_hi_mid = static_cast<int>(kf);
   int x_hi = x_hi_mid >> 3;

libc/test/src/math/performance_testing/expf16_perf.cpp

@@ -1,4 +1,4 @@
-//===-- Performancel test for expf16 --------------------------------------===//
+//===-- Performance test for expf16 ---------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.

libc/test/src/math/smoke/expf16_test.cpp

@@ -21,7 +21,7 @@ TEST_F(LlvmLibcExpf16Test, SpecialNumbers) {
   EXPECT_FP_EQ_ALL_ROUNDING(aNaN, LIBC_NAMESPACE::expf16(aNaN));
   EXPECT_MATH_ERRNO(0);
 
-  EXPECT_FP_EQ_WITH_EXCEPTION(sNaN, LIBC_NAMESPACE::expf16(sNaN), FE_INVALID);
+  EXPECT_FP_EQ_WITH_EXCEPTION(aNaN, LIBC_NAMESPACE::expf16(sNaN), FE_INVALID);
   EXPECT_MATH_ERRNO(0);
 
   EXPECT_FP_EQ_ALL_ROUNDING(inf, LIBC_NAMESPACE::expf16(inf));