[dpdk-dev] [PATCH v2 2/3] eal: add static endianness conversion macros

[Adrien Mazarguil <adrien.mazarguil@6wind.com>]

These macros resolve to constant expressions that allow developers to
perform endianness conversion on static/const objects, even outside of
function scope as they do not translate to function calls.

This is most useful for static initializers and constant values (whenever
it has to be performed at compilation time). Run-time endianness conversion
of variable values should keep using rte_*_to_*() calls for best
performance.

Signed-off-by: Adrien Mazarguil <adrien.mazarguil@6wind.com>
---
 .../common/include/generic/rte_byteorder.h      | 70 ++++++++++++++++----
 1 file changed, 56 insertions(+), 14 deletions(-)

diff --git a/lib/librte_eal/common/include/generic/rte_byteorder.h b/lib/librte_eal/common/include/generic/rte_byteorder.h
index df8cc84..e5e820d 100644
--- a/lib/librte_eal/common/include/generic/rte_byteorder.h
+++ b/lib/librte_eal/common/include/generic/rte_byteorder.h
@@ -74,6 +74,59 @@
 #elif defined __LITTLE_ENDIAN__
 #define RTE_BYTE_ORDER RTE_LITTLE_ENDIAN
 #endif
+#if !defined(RTE_BYTE_ORDER)
+#error Unknown endianness.
+#endif
+
+#define RTE_STATIC_BSWAP16(v) \
+	((((uint16_t)(v) & UINT16_C(0x00ff)) << 8) | \
+	 (((uint16_t)(v) & UINT16_C(0xff00)) >> 8))
+
+#define RTE_STATIC_BSWAP32(v) \
+	((((uint32_t)(v) & UINT32_C(0x000000ff)) << 24) | \
+	 (((uint32_t)(v) & UINT32_C(0x0000ff00)) <<  8) | \
+	 (((uint32_t)(v) & UINT32_C(0x00ff0000)) >>  8) | \
+	 (((uint32_t)(v) & UINT32_C(0xff000000)) >> 24))
+
+#define RTE_STATIC_BSWAP64(v) \
+	((((uint64_t)(v) & UINT64_C(0x00000000000000ff)) << 56) | \
+	 (((uint64_t)(v) & UINT64_C(0x000000000000ff00)) << 40) | \
+	 (((uint64_t)(v) & UINT64_C(0x0000000000ff0000)) << 24) | \
+	 (((uint64_t)(v) & UINT64_C(0x00000000ff000000)) <<  8) | \
+	 (((uint64_t)(v) & UINT64_C(0x000000ff00000000)) >>  8) | \
+	 (((uint64_t)(v) & UINT64_C(0x0000ff0000000000)) >> 24) | \
+	 (((uint64_t)(v) & UINT64_C(0x00ff000000000000)) >> 40) | \
+	 (((uint64_t)(v) & UINT64_C(0xff00000000000000)) >> 56))
+
+/*
+ * These macros are functionally similar to rte_cpu_to_(be|le)(16|32|64)(),
+ * they take values in host CPU order and return them converted to the
+ * intended endianness.
+ *
+ * They resolve at compilation time to integer constants which can safely be
+ * used with static initializers, since those cannot involve function calls.
+ *
+ * On the other hand, they are not as optimized as their rte_cpu_to_*()
+ * counterparts, therefore applications should refrain from using them on
+ * variable values, particularly inside performance-sensitive code.
+ */
+#if RTE_BYTE_ORDER == RTE_BIG_ENDIAN
+#define RTE_BE16(v) (rte_be16_t)(v)
+#define RTE_BE32(v) (rte_be32_t)(v)
+#define RTE_BE64(v) (rte_be64_t)(v)
+#define RTE_LE16(v) (rte_le16_t)(RTE_STATIC_BSWAP16(v))
+#define RTE_LE32(v) (rte_le32_t)(RTE_STATIC_BSWAP32(v))
+#define RTE_LE64(v) (rte_le64_t)(RTE_STATIC_BSWAP64(v))
+#elif RTE_BYTE_ORDER == RTE_LITTLE_ENDIAN
+#define RTE_BE16(v) (rte_be16_t)(RTE_STATIC_BSWAP16(v))
+#define RTE_BE32(v) (rte_be32_t)(RTE_STATIC_BSWAP32(v))
+#define RTE_BE64(v) (rte_be64_t)(RTE_STATIC_BSWAP64(v))
+#define RTE_LE16(v) (rte_be16_t)(v)
+#define RTE_LE32(v) (rte_be32_t)(v)
+#define RTE_LE64(v) (rte_be64_t)(v)
+#else
+#error Unsupported endianness.
+#endif
 
 /*
  * The following types should be used when handling values according to a
@@ -98,8 +151,7 @@ typedef uint64_t rte_le64_t; /**< 64-bit little-endian value. */
 static inline uint16_t
 rte_constant_bswap16(uint16_t x)
 {
-	return (uint16_t)(((x & 0x00ffU) << 8) |
-		((x & 0xff00U) >> 8));
+	return RTE_STATIC_BSWAP16(x);
 }
 
 /*
@@ -111,10 +163,7 @@ rte_constant_bswap16(uint16_t x)
 static inline uint32_t
 rte_constant_bswap32(uint32_t x)
 {
-	return  ((x & 0x000000ffUL) << 24) |
-		((x & 0x0000ff00UL) << 8) |
-		((x & 0x00ff0000UL) >> 8) |
-		((x & 0xff000000UL) >> 24);
+	return RTE_STATIC_BSWAP32(x);
 }
 
 /*
@@ -126,14 +175,7 @@ rte_constant_bswap32(uint32_t x)
 static inline uint64_t
 rte_constant_bswap64(uint64_t x)
 {
-	return  ((x & 0x00000000000000ffULL) << 56) |
-		((x & 0x000000000000ff00ULL) << 40) |
-		((x & 0x0000000000ff0000ULL) << 24) |
-		((x & 0x00000000ff000000ULL) <<  8) |
-		((x & 0x000000ff00000000ULL) >>  8) |
-		((x & 0x0000ff0000000000ULL) >> 24) |
-		((x & 0x00ff000000000000ULL) >> 40) |
-		((x & 0xff00000000000000ULL) >> 56);
+	return RTE_STATIC_BSWAP64(x);
 }
 
 
-- 
2.1.4