RIOT-OS · maribu · Jan 30, 2024 · Jan 30, 2024 · Jan 30, 2024
diff --git a/sys/libc/include/endian.h b/sys/libc/include/endian.h
@@ -0,0 +1,114 @@
+/*
+ * Copyright (C) 2024 Otto-von-Guericke-Universität Magdeburg
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser General
+ * Public License v2.1. See the file LICENSE in the top level directory for more
+ * details.
+ */
+
+/**
+ * @addtogroup posix
+ * @{
+ */
+/**
+ * @file
+ * @brief       libc header for endian conversion
+ *
+ * @author      Marian Buschsieweke <marian.buschsieweke@posteo.net>
+ */
+
+#ifndef ENDIAN_H
+#define ENDIAN_H
+
+#include <stdint.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#ifdef DOXYGEN
+/**
+ * @brief   A numeric constant representing little endian byte order
+ */
+#define LITTLE_ENDIAN   implementation_defined
+
+/**
+ * @brief   A numeric constant representing big endian byte order
+ */
+#define BIG_ENDIAN      implementation_defined
+
+/**
+ * @brief   A numeric constant representing PDP endian byte order
+ */
+#define PDP_ENDIAN      implementation_defined
+
+/**
+ * @brief   The byte order of this machines indicated by the constant
+ *          @ref BIG_ENDIAN or @ref LITTLE_ENDIAN
+ *
+ * @note    This numeric constant is available at preprocessor time, so you
+ *          can compare this to @ref BIG_ENDIAN or @ref LITTLE_ENDIAN in
+ *          `#if` directives.
+ */
+#define BYTE_ORDER      <LITTLE_ENDIAN or BIG_ENDIAN>
+
+uint16_t htobe16(uint16_t host_16bits);         /**< host to big endian, 16 bit */
+uint16_t htole16(uint16_t host_16bits);         /**< host to little endian, 16 bit */
+uint16_t be16toh(uint16_t big_endian_16bits);   /**< big endian to host, 16 bit */
+uint16_t le16toh(uint16_t little_endian_16bits);/**< little endian to host, 16 bit */
+
+uint32_t htobe32(uint32_t host_32bits);         /**< host to big endian, 32 bit */
+uint32_t htole32(uint32_t host_32bits);         /**< host to little endian, 32 bit */
+uint32_t be32toh(uint32_t big_endian_32bits);   /**< big endian to host, 32 bit */
+uint32_t le32toh(uint32_t little_endian_32bits);/**< little endian to host, 32 bit */
+
+uint64_t htobe64(uint64_t host_64bits);         /**< host to big endian, 64 bit */
+uint64_t htole64(uint64_t host_64bits);         /**< host to little endian, 64 bit */
+uint64_t be64toh(uint64_t big_endian_64bits);   /**< big endian to host, 64 bit */
+uint64_t le64toh(uint64_t little_endian_64bits);/**< little endian to host, 64 bit */
+
+#else /* DOXYGEN */
+
+#define LITTLE_ENDIAN   _LITTLE_ENDIAN
+#define BIG_ENDIAN      _BIG_ENDIAN
+#define PDP_ENDIAN      _PDP_ENDIAN
+#define BYTE_ORDER      _BYTE_ORDER
+
+#if BYTE_ORDER == LITTLE_ENDIAN
+#  define htobe16(_x) __builtin_bswap16(_x)
+#  define htole16(_x) ((__uint16_t)(_x))
+#  define be16toh(_x) __builtin_bswap16(_x)
+#  define le16toh(_x) ((__uint16_t)(_x))
+#  define htobe32(_x) __builtin_bswap32(_x)
+#  define htole32(_x) ((__uint32_t)(_x))
+#  define be32toh(_x) __builtin_bswap32(_x)
+#  define le32toh(_x) ((__uint32_t)(_x))
+#  define htobe64(_x) __builtin_bswap64(_x)
+#  define htole64(_x) ((__uint64_t)(_x))
+#  define be64toh(_x) __builtin_bswap64(_x)
+#  define le64toh(_x) ((__uint64_t)(_x))
+#elif BYTE_ORDER == BIG_ENDIAN
+#  define htole16(_x) __builtin_bswap16(_x)
+#  define htobe16(_x) ((__uint16_t)(_x))
+#  define le16toh(_x) __builtin_bswap16(_x)
+#  define be16toh(_x) ((__uint16_t)(_x))
+#  define htole32(_x) __builtin_bswap32(_x)
+#  define htobe32(_x) ((__uint32_t)(_x))
+#  define le32toh(_x) __builtin_bswap32(_x)
+#  define be32toh(_x) ((__uint32_t)(_x))
+#  define htole64(_x) __builtin_bswap64(_x)
+#  define htobe64(_x) ((__uint64_t)(_x))
+#  define le64toh(_x) __builtin_bswap64(_x)
+#  define be64toh(_x) ((__uint64_t)(_x))
+#else
+#  error "Byte order not supported"
+#endif
+
+#endif /* DOXYGEN */
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* ENDIAN_H */
+/** @} */
@@ -8,6 +8,7 @@
 
 #include <stdint.h>
 #include <string.h>
+#include <endian.h>
 #include "string_utils.h"
 
 #include "tests-libc.h"
@@ -39,11 +40,64 @@ static void test_libc_memchk(void)
     TEST_ASSERT(memchk(buffer, 0xff, sizeof(buffer)) == &buffer[5]);
 }
 
+/**
+ * @name    Unit test ensuring `<endian.h>` is provided and correct across
+ *          all platforms
+ * @{
+ */
+union u16 {
+    uint8_t as_bytes[2];
+    uint16_t as_number;
+};
+
+union u32 {
+    uint8_t as_bytes[4];
+    uint32_t as_number;
+};
+
+union u64 {
+    uint8_t as_bytes[8];
+    uint64_t as_number;
+};
+
+static void test_libc_endian(void)
+{
+    /* format the numbers 0x0102, 0x01020304 and 0x0102030405060708
+     * in little/big endian format by hand: */
+    const uint16_t u16_host = 0x0102;
+    const union u16 u16_be = { .as_bytes = { 0x01, 0x02 } };
+    const union u16 u16_le = { .as_bytes = { 0x02, 0x01 } };
+    const uint32_t u32_host = 0x01020304;
+    const union u32 u32_be = { .as_bytes = { 0x01, 0x02, 0x03, 0x04 } };
+    const union u32 u32_le = { .as_bytes = { 0x04, 0x03, 0x02, 0x01 } };
+    const uint64_t u64_host = 0x0102030405060708;
+    const union u64 u64_be = { .as_bytes = { 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08 } };
+    const union u64 u64_le = { .as_bytes = { 0x08, 0x07, 0x06, 0x05, 0x04, 0x03, 0x02, 0x01 } };
+
+    /* check from host to big/little endian */
+    TEST_ASSERT_EQUAL_INT(htobe16(u16_host), u16_be.as_number);
+    TEST_ASSERT_EQUAL_INT(htole16(u16_host), u16_le.as_number);
+    TEST_ASSERT_EQUAL_INT(htobe32(u32_host), u32_be.as_number);
+    TEST_ASSERT_EQUAL_INT(htole32(u32_host), u32_le.as_number);
+    TEST_ASSERT_EQUAL_INT(htobe64(u64_host), u64_be.as_number);
+    TEST_ASSERT_EQUAL_INT(htole64(u64_host), u64_le.as_number);
+
+    /* check little/big endian to host */
+    TEST_ASSERT_EQUAL_INT(be16toh(u16_be.as_number), u16_host);
+    TEST_ASSERT_EQUAL_INT(le16toh(u16_le.as_number), u16_host);
+    TEST_ASSERT_EQUAL_INT(be32toh(u32_be.as_number), u32_host);
+    TEST_ASSERT_EQUAL_INT(le32toh(u32_le.as_number), u32_host);
+    TEST_ASSERT_EQUAL_INT(be64toh(u64_be.as_number), u64_host);
+    TEST_ASSERT_EQUAL_INT(le64toh(u64_le.as_number), u64_host);
+}
+/** @} */
+
 Test *tests_libc_tests(void)
 {
     EMB_UNIT_TESTFIXTURES(fixtures) {
         new_TestFixture(test_libc_strscpy),
         new_TestFixture(test_libc_memchk),
+        new_TestFixture(test_libc_endian),
     };
 
     EMB_UNIT_TESTCALLER(libc_tests, NULL, NULL, fixtures);