1 files changed, 71 insertions, 0 deletions
diff --git a/pl/math/coshf_1u9.c b/pl/math/coshf_1u9.c
new file mode 100644
index 0000000..c125c92
--- /dev/null
+++ b/pl/math/coshf_1u9.c
@@ -0,0 +1,71 @@
+/*
+ * Single-precision cosh(x) function.
+ *
+ * Copyright (c) 2022-2023, Arm Limited.
+ * SPDX-License-Identifier: MIT OR Apache-2.0 WITH LLVM-exception
+ */
+
+#include "math_config.h"
+#include "pl_sig.h"
+#include "pl_test.h"
+
+#define AbsMask 0x7fffffff
+#define TinyBound 0x20000000 /* 0x1p-63: Round to 1 below this.  */
+#define SpecialBound                                                           \
+  0x42ad496c /* 0x1.5a92d8p+6: expf overflows above this, so have to use       \
+		special case.  */
+
+float
+optr_aor_exp_f32 (float);
+
+static NOINLINE float
+specialcase (float x, uint32_t iax)
+{
+  if (iax == 0x7f800000)
+    return INFINITY;
+  if (iax > 0x7f800000)
+    return __math_invalidf (x);
+  if (iax <= TinyBound)
+    /* For tiny x, avoid underflow by just returning 1.  */
+    return 1;
+  /* Otherwise SpecialBound <= |x| < Inf. x is too large to calculate exp(x)
+     without overflow, so use exp(|x|/2) instead. For large x cosh(x) is
+     dominated by exp(x), so return:
+     cosh(x) ~= (exp(|x|/2))^2 / 2.  */
+  float t = optr_aor_exp_f32 (asfloat (iax) / 2);
+  return (0.5 * t) * t;
+}
+
+/* Approximation for single-precision cosh(x) using exp.
+   cosh(x) = (exp(x) + exp(-x)) / 2.
+   The maximum error is 1.89 ULP, observed for |x| > SpecialBound:
+   coshf(0x1.65898cp+6) got 0x1.f00aep+127 want 0x1.f00adcp+127.
+   The maximum error observed for TinyBound < |x| < SpecialBound is 1.02 ULP:
+   coshf(0x1.50a3cp+0) got 0x1.ff21dcp+0 want 0x1.ff21dap+0.  */
+float
+coshf (float x)
+{
+  uint32_t ix = asuint (x);
+  uint32_t iax = ix & AbsMask;
+  float ax = asfloat (iax);
+
+  if (unlikely (iax <= TinyBound || iax >= SpecialBound))
+    {
+      /* x is tiny, large or special.  */
+      return specialcase (x, iax);
+    }
+
+  /* Compute cosh using the definition:
+     coshf(x) = exp(x) / 2 + exp(-x) / 2.  */
+  float t = optr_aor_exp_f32 (ax);
+  return 0.5f * t + 0.5f / t;
+}
+
+PL_SIG (S, F, 1, cosh, -10.0, 10.0)
+PL_TEST_ULP (coshf, 1.89)
+PL_TEST_INTERVAL (coshf, 0, 0x1p-63, 100)
+PL_TEST_INTERVAL (coshf, 0, 0x1.5a92d8p+6, 80000)
+PL_TEST_INTERVAL (coshf, 0x1.5a92d8p+6, inf, 2000)
+PL_TEST_INTERVAL (coshf, -0, -0x1p-63, 100)
+PL_TEST_INTERVAL (coshf, -0, -0x1.5a92d8p+6, 80000)
+PL_TEST_INTERVAL (coshf, -0x1.5a92d8p+6, -inf, 2000)