[libc-commits] [libc] [libc][math][c23] Add exp2m1f C23 math function (PR #86996)

[via libc-commits]

================
@@ -0,0 +1,182 @@
+//===-- Implementation of exp2m1f 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/exp2m1f.h"
+#include "src/__support/FPUtil/FEnvImpl.h"
+#include "src/__support/FPUtil/FPBits.h"
+#include "src/__support/FPUtil/PolyEval.h"
+#include "src/__support/FPUtil/except_value_utils.h"
+#include "src/__support/FPUtil/multiply_add.h"
+#include "src/__support/FPUtil/rounding_mode.h"
+#include "src/__support/common.h"
+#include "src/__support/macros/optimization.h"
+#include "src/__support/macros/properties/cpu_features.h"
+#include "src/errno/libc_errno.h"
+
+#include "explogxf.h"
+
+namespace LIBC_NAMESPACE {
+
+static constexpr size_t N_EXCEPTS_LO = 8;
+
+static constexpr fputil::ExceptValues<float, N_EXCEPTS_LO> EXP2M1F_EXCEPTS_LO =
+    {{
+        // (input, RZ output, RU offset, RD offset, RN offset)
+        // x = 0x1.36dc8ep-36, exp2m1f(x) = 0x1.aef212p-37 (RZ)
+        {0x2d9b'6e47U, 0x2d57'7909U, 1U, 0U, 0U},
+        // x = 0x1.224936p-19, exp2m1f(x) = 0x1.926c0ep-20 (RZ)
+        {0x3611'249bU, 0x35c9'3607U, 1U, 0U, 1U},
+        // x = 0x1.d16d2p-20, exp2m1f(x) = 0x1.429becp-20 (RZ)
+        {0x35e8'b690U, 0x35a1'4df6U, 1U, 0U, 1U},
+        // x = 0x1.17949ep-14, exp2m1f(x) = 0x1.8397p-15 (RZ)
+        {0x388b'ca4fU, 0x3841'cb80U, 1U, 0U, 1U},
+        // x = -0x1.9c3e1ep-38, exp2m1f(x) = -0x1.1dbeacp-38 (RZ)
+        {0xacce'1f0fU, 0xac8e'df56U, 0U, 1U, 0U},
+        // x = -0x1.4d89b4p-32, exp2m1f(x) = -0x1.ce61b6p-33 (RZ)
+        {0xafa6'c4daU, 0xaf67'30dbU, 0U, 1U, 1U},
+        // x = -0x1.a6eac4p-10, exp2m1f(x) = -0x1.24fadap-10 (RZ)
+        {0xbad3'7562U, 0xba92'7d6dU, 0U, 1U, 1U},
+        // x = -0x1.e7526ep-6, exp2m1f(x) = -0x1.4e53dep-6 (RZ)
+        {0xbcf3'a937U, 0xbca7'29efU, 0U, 1U, 1U},
+    }};
+
+static constexpr size_t N_EXCEPTS_HI = 2;
+
+static constexpr fputil::ExceptValues<float, N_EXCEPTS_HI> EXP2M1F_EXCEPTS_HI =
+    {{
+        // (input, RZ output, RU offset, RD offset, RN offset)
+        // x = 0x1.16a972p-1, exp2m1f(x) = 0x1.d545b2p-2 (RZ)
+        {0x3f0b'54b9U, 0x3eea'a2d9U, 1U, 0U, 0U},
+        // x = -0x1.9f12acp-5, exp2m1f(x) = -0x1.1ab68cp-5 (RZ)
+        {0xbd4f'8956U, 0xbd0d'5b46U, 0U, 1U, 0U},
+    }};
----------------
lntue wrote:

When FMA is not available, there is another exceptional cases: `x = -0x1.de7b9cp-5f`, which would fail on RZ.

https://github.com/llvm/llvm-project/pull/86996