pl/math: Add scalar log1pf

The new routine uses a polynomial on a reduced interval. Worst-case
error is about 2.1 ULP, with an option in math_config.h to use Horner
instead of Estrin for the polynomial, which gives worst-case error of
1.3 ULP.

1 files changed, 14 insertions, 0 deletions

diff --git a/pl/math/log1pf_data.c b/pl/math/log1pf_data.c
new file mode 100644
index 0000000..d7bc95c
--- /dev/null
+++ b/pl/math/log1pf_data.c
@@ -0,0 +1,14 @@
+/*
+ * Data used in single-precision log1p(x) function.
+ *
+ * Copyright (c) 2022, Arm Limited.
+ * SPDX-License-Identifier: MIT OR Apache-2.0 WITH LLVM-exception
+ */
+#include "math_config.h"
+
+/* Polynomial coefficients generated using floating-point minimax
+   algorithm, see tools/log1pf.sollya for details.  */
+const struct log1pf_data __log1pf_data
+  = {.coeffs = {-0x1p-1f, 0x1.5555aap-2f, -0x1.000038p-2f, 0x1.99675cp-3f,
+		-0x1.54ef78p-3f, 0x1.28a1f4p-3f, -0x1.0da91p-3f, 0x1.abcb6p-4f,
+		-0x1.6f0d5ep-5f}};