[libc-commits] [libc] [libc][termios] Fix termios compatibility with glibc 2.42 or after. (PR #211039)

[via libc-commits]

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+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+/// Speed translation utilities for termios.
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_TERMIOS_LINUX_SPEED_UTILS_H
+#define LLVM_LIBC_SRC_TERMIOS_LINUX_SPEED_UTILS_H
+
+#include "hdr/termios_macros.h"
+#include "hdr/types/speed_t.h"
+#include "src/__support/macros/config.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+// glibc 2.42 changed the behavior of the termios Bxxx constants:
+// - Before glibc 2.42, the Bxxx constants correspond to the kernel speed
+// bitmasks
+//   directly (e.g. B50 = 1).
+// - Starting from glibc 2.42, to support arbitrary baud rates numerically, the
+//   Bxxx constants are defined as their actual integer values (e.g. B50 = 50).
+// In this case, we need to translate between the host's numerical speeds and
+// the kernel's speed bitmasks.
+// - If B50 == 1, then the host uses the kernel's bitmasks directly (no
+//   translation).
+// - If B50 is not 1 (e.g. B50 == 50 in glibc >= 2.42), we apply
+//   translation.
+#if (B50 == 1)
+
+LIBC_INLINE constexpr speed_t encode_speed(speed_t speed) { return speed; }
+LIBC_INLINE constexpr speed_t decode_speed(speed_t speed) { return speed; }
+
+#else // Overlay mode with numerical speeds (e.g. glibc)
+
+LIBC_INLINE constexpr speed_t encode_speed(speed_t speed) {
+  switch (speed) {
+  case 0:
+    return 0;
+  case 50:
+    return 0000001;
+  case 75:
+    return 0000002;
+  case 110:
+    return 0000003;
+  case 134:
+    return 0000004;
+  case 150:
+    return 0000005;
+  case 200:
+    return 0000006;
+  case 300:
+    return 0000007;
+  case 600:
+    return 0000010;
+  case 1200:
+    return 0000011;
+  case 1800:
+    return 0000012;
+  case 2400:
+    return 0000013;
+  case 4800:
+    return 0000014;
+  case 9600:
+    return 0000015;
+  case 19200:
+    return 0000016;
+  case 38400:
+    return 0000017;
+  case 57600:
+    return 0010001;
+  case 115200:
+    return 0010002;
+  case 230400:
+    return 0010003;
+  case 460800:
+    return 0010004;
+  case 500000:
+    return 0010005;
+  case 576000:
+    return 0010006;
+  case 921600:
+    return 0010007;
+  case 1000000:
+    return 0010010;
+  case 1152000:
+    return 0010011;
+  case 1500000:
+    return 0010012;
+  case 2000000:
+    return 0010013;
+  case 2500000:
+    return 0010014;
+  case 3000000:
+    return 0010015;
+  case 3500000:
+    return 0010016;
+  case 4000000:
+    return 0010017;
+  default:
+    return speed;
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lntue wrote:

Done.

https://github.com/llvm/llvm-project/pull/211039