[libc-commits] [libc] [libc][math] Refactor sinh to header-only (PR #177745)

[via libc-commits]

https://github.com/Pratyush378 created https://github.com/llvm/llvm-project/pull/177745

Refactor `sinh(double)` to header-only following `exp.h`, `cosh.h` pattern.
Uses `expm1()` + small-x approximation.

Part of #177643

>From ed01cc721470d3ded153cc3ebd41fd02e4026b93 Mon Sep 17 00:00:00 2001
From: Pratyush <pratyush6566 at gmail.com>
Date: Sat, 24 Jan 2026 13:44:36 +0530
Subject: [PATCH] [libc][math] Refactor sinh to header-only Part of #177643

---
 libc/src/math/generic/sinh.cpp |  1 +
 libc/src/math/sinh.h           | 32 +++++++++++++++++++++++++++++---
 2 files changed, 30 insertions(+), 3 deletions(-)
 create mode 100644 libc/src/math/generic/sinh.cpp

diff --git a/libc/src/math/generic/sinh.cpp b/libc/src/math/generic/sinh.cpp
new file mode 100644
index 0000000000000..993e1a8951dfb
--- /dev/null
+++ b/libc/src/math/generic/sinh.cpp
@@ -0,0 +1 @@
+#include "src/math/sinh.h" 
\ No newline at end of file
diff --git a/libc/src/math/sinh.h b/libc/src/math/sinh.h
index b87471c2bfcc2..57489d684c8a6 100644
--- a/libc/src/math/sinh.h
+++ b/libc/src/math/sinh.h
@@ -9,12 +9,38 @@
 #ifndef LLVM_LIBC_SRC_MATH_SINH_H
 #define LLVM_LIBC_SRC_MATH_SINH_H
 
+#include "src/__support/FPUtil/FPBits.h"
+#include "src/__support/math/expm1.h"
 #include "src/__support/macros/config.h"
+#include "src/__support/macros/optimization.h"
 
-namespace LIBC_NAMESPACE_DECL {
+namespace LIBC_NAMESPACE {
 
-double sinh(double x);
+double sinh(double x) {
+  fputil::FPBits<double> xbits(x);
+  uint64_t xbits_u = xbits.bits;
+  uint32_t xpt = (xbits_u >> 52) & 0x7ffU;
 
-} // namespace LIBC_NAMESPACE_DECL
+  // sinh(±Inf) = ±Inf, sinh(NaN) = NaN
+  if (xpt >= 0x7ff) {
+    if (xbits_u == (0x7ffULL << 52)) // Inf
+      return x;
+    return x + 0.0; // NaN
+  }
+
+  // |x| < 2^-9: sinh(x) ≈ x + x^3/6
+  if (xpt < 0x3c9) {
+    double x2 = x * x;
+    return x + x * x2 * (1.0 / 6.0);
+  }
+
+  // Large |x|: sinh(x) ≈ sign(x)*0.5*exp(|x|)
+  double h = x < 0.0 ? -x : x;
+  double t = expm1(h);
+  double s = 0.5 * (t + 1.0);
+  return x >= 0.0 ? s : -s;
+}
+
+} // namespace LIBC_NAMESPACE
 
 #endif // LLVM_LIBC_SRC_MATH_SINH_H