endian: add constant versions.

Sometimes you really need a compile-time constant, but there's no generic way
to create a macro which does this and only evaluates its argument once.

Thus we need specific const macros.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

ccan/endian/endian.h

@@ -4,6 +4,59 @@
 #include <stdint.h>
 #include "config.h"
 
+/**
+ * BSWAP_16_CONST - reverse bytes in a constant uint16_t value.
+ * @val: constant value whose bytes to swap.
+ *
+ * Designed to be usable in constant-requiring initializers.
+ *
+ * Example:
+ *	struct mystruct {
+ *		char buf[BSWAP_16_CONST(0x1234)];
+ *	};
+ */
+#define BSWAP_16_CONST(val)				\
+	((((uint16_t)val & 0x00ff) << 8)	\
+	 | (((uint16_t)val & 0xff00) >> 8))
+
+/**
+ * BSWAP_32_CONST - reverse bytes in a constant uint32_t value.
+ * @val: constant value whose bytes to swap.
+ *
+ * Designed to be usable in constant-requiring initializers.
+ *
+ * Example:
+ *	struct mystruct {
+ *		char buf[BSWAP_32_CONST(0xff000000)];
+ *	};
+ */
+#define BSWAP_32_CONST(val)				\
+	((((uint32_t)val & 0x000000ff) << 24)		\
+	 | (((uint32_t)val & 0x0000ff00) << 8)		\
+	 | (((uint32_t)val & 0x00ff0000) >> 8)		\
+	 | (((uint32_t)val & 0xff000000) >> 24))
+
+/**
+ * BSWAP_64_CONST - reverse bytes in a constant uint64_t value.
+ * @val: constantvalue whose bytes to swap.
+ *
+ * Designed to be usable in constant-requiring initializers.
+ *
+ * Example:
+ *	struct mystruct {
+ *		char buf[BSWAP_64_CONST(0xff00000000000000ULL)];
+ *	};
+ */
+#define BSWAP_64_CONST(val)					\
+	((((uint64_t)val & 0x00000000000000ffULL) << 56)	\
+	 | (((uint64_t)val & 0x000000000000ff00ULL) << 40)	\
+	 | (((uint64_t)val & 0x0000000000ff0000ULL) << 24)	\
+	 | (((uint64_t)val & 0x00000000ff000000ULL) << 8)	\
+	 | (((uint64_t)val & 0x000000ff00000000ULL) >> 8)	\
+	 | (((uint64_t)val & 0x0000ff0000000000ULL) >> 24)	\
+	 | (((uint64_t)val & 0x00ff000000000000ULL) >> 40)	\
+	 | (((uint64_t)val & 0xff00000000000000ULL) >> 56))
+
 #if HAVE_BYTESWAP_H
 #include <byteswap.h>
 #else
@@ -17,8 +70,7 @@
  */
 static inline uint16_t bswap_16(uint16_t val)
 {
-	return ((val & (uint16_t)0x00ffU) << 8)
-		| ((val & (uint16_t)0xff00U) >> 8);
+	return BSWAP_16_CONST(val);
 }
 
 /**
@@ -31,10 +83,7 @@ static inline uint16_t bswap_16(uint16_t val)
  */
 static inline uint32_t bswap_32(uint32_t val)
 {
-	return ((val & (uint32_t)0x000000ffUL) << 24)
-		| ((val & (uint32_t)0x0000ff00UL) <<  8)
-		| ((val & (uint32_t)0x00ff0000UL) >>  8)
-		| ((val & (uint32_t)0xff000000UL) >> 24);
+	return BSWAP_32_CONST(val);
 }
 #endif /* !HAVE_BYTESWAP_H */
 
@@ -50,14 +99,7 @@ static inline uint32_t bswap_32(uint32_t val)
  */
 static inline uint64_t bswap_64(uint64_t val)
 {
-	return ((val & (uint64_t)0x00000000000000ffULL) << 56)
-		| ((val & (uint64_t)0x000000000000ff00ULL) << 40)
-		| ((val & (uint64_t)0x0000000000ff0000ULL) << 24)
-		| ((val & (uint64_t)0x00000000ff000000ULL) <<  8)
-		| ((val & (uint64_t)0x000000ff00000000ULL) >>  8)
-		| ((val & (uint64_t)0x0000ff0000000000ULL) >> 24)
-		| ((val & (uint64_t)0x00ff000000000000ULL) >> 40)
-		| ((val & (uint64_t)0xff00000000000000ULL) >> 56);
+	return BSWAP_64_CONST(val);
 }
 #endif
 
@@ -68,17 +110,106 @@ static inline uint64_t bswap_64(uint64_t val)
 #error "Can't compile for both big and little endian."
 #endif
 
+#if HAVE_LITTLE_ENDIAN
+/**
+ * CPU_TO_LE64_CONST - convert a constant uint64_t value to little-endian
+ * @native: constant to convert
+ */
+#define CPU_TO_LE64_CONST(native) (native)
+
+/**
+ * CPU_TO_LE32_CONST - convert a constant uint32_t value to little-endian
+ * @native: constant to convert
+ */
+#define CPU_TO_LE32_CONST(native) (native)
+
+/**
+ * CPU_TO_LE16_CONST - convert a constant uint16_t value to little-endian
+ * @native: constant to convert
+ */
+#define CPU_TO_LE16_CONST(native) (native)
+
+/**
+ * LE64_TO_CPU_CONST - convert a little-endian uint64_t constant
+ * @le_val: little-endian constant to convert
+ */
+#define LE64_TO_CPU_CONST(le_val) (le_val)
+
+/**
+ * LE32_TO_CPU_CONST - convert a little-endian uint32_t constant
+ * @le_val: little-endian constant to convert
+ */
+#define LE32_TO_CPU_CONST(le_val) (le_val)
+
+/**
+ * LE16_TO_CPU_CONST - convert a little-endian uint16_t constant
+ * @le_val: little-endian constant to convert
+ */
+#define LE16_TO_CPU_CONST(le_val) (le_val)
+
+#else /* ... HAVE_BIG_ENDIAN */
+#define CPU_TO_LE64_CONST(native) BSWAP_64_CONST(native)
+#define CPU_TO_LE32_CONST(native) BSWAP_32_CONST(native)
+#define CPU_TO_LE16_CONST(native) BSWAP_16_CONST(native)
+#define LE64_TO_CPU_CONST(le_val) BSWAP_64_CONST(le_val)
+#define LE32_TO_CPU_CONST(le_val) BSWAP_32_CONST(le_val)
+#define LE16_TO_CPU_CONST(le_val) BSWAP_16_CONST(le_val)
+#endif /* HAVE_BIG_ENDIAN */
+
+#if HAVE_BIG_ENDIAN
+/**
+ * CPU_TO_BE64_CONST - convert a constant uint64_t value to big-endian
+ * @native: constant to convert
+ */
+#define CPU_TO_BE64_CONST(native) (native)
+
+/**
+ * CPU_TO_BE32_CONST - convert a constant uint32_t value to big-endian
+ * @native: constant to convert
+ */
+#define CPU_TO_BE32_CONST(native) (native)
+
+/**
+ * CPU_TO_BE16_CONST - convert a constant uint16_t value to big-endian
+ * @native: constant to convert
+ */
+#define CPU_TO_BE16_CONST(native) (native)
+
+/**
+ * BE64_TO_CPU_CONST - convert a big-endian uint64_t constant
+ * @le_val: big-endian constant to convert
+ */
+#define BE64_TO_CPU_CONST(le_val) (le_val)
+
+/**
+ * BE32_TO_CPU_CONST - convert a big-endian uint32_t constant
+ * @le_val: big-endian constant to convert
+ */
+#define BE32_TO_CPU_CONST(le_val) (le_val)
+
+/**
+ * BE16_TO_CPU_CONST - convert a big-endian uint16_t constant
+ * @le_val: big-endian constant to convert
+ */
+#define BE16_TO_CPU_CONST(le_val) (le_val)
+
+#else /* ... HAVE_LITTLE_ENDIAN */
+#define CPU_TO_BE64_CONST(native) BSWAP_64_CONST(native)
+#define CPU_TO_BE32_CONST(native) BSWAP_32_CONST(native)
+#define CPU_TO_BE16_CONST(native) BSWAP_16_CONST(native)
+#define BE64_TO_CPU_CONST(le_val) BSWAP_64_CONST(le_val)
+#define BE32_TO_CPU_CONST(le_val) BSWAP_32_CONST(le_val)
+#define BE16_TO_CPU_CONST(le_val) BSWAP_16_CONST(le_val)
+#endif /* HAVE_LITTE_ENDIAN */
+
+
 /**
  * cpu_to_le64 - convert a uint64_t value to little-endian
  * @native: value to convert
  */
 static inline uint64_t cpu_to_le64(uint64_t native)
 {
-#if HAVE_LITTLE_ENDIAN
-	return native;
-#else
-	return bswap_64(native);
-#endif
+	return CPU_TO_LE64_CONST(native);
 }
 
 /**
@@ -87,11 +218,7 @@ static inline uint64_t cpu_to_le64(uint64_t native)
  */
 static inline uint32_t cpu_to_le32(uint32_t native)
 {
-#if HAVE_LITTLE_ENDIAN
-	return native;
-#else
-	return bswap_32(native);
-#endif
+	return CPU_TO_LE32_CONST(native);
 }
 
 /**
@@ -100,11 +227,7 @@ static inline uint32_t cpu_to_le32(uint32_t native)
  */
 static inline uint16_t cpu_to_le16(uint16_t native)
 {
-#if HAVE_LITTLE_ENDIAN
-	return native;
-#else
-	return bswap_16(native);
-#endif
+	return CPU_TO_LE16_CONST(native);
 }
 
 /**
@@ -113,11 +236,7 @@ static inline uint16_t cpu_to_le16(uint16_t native)
  */
 static inline uint64_t le64_to_cpu(uint64_t le_val)
 {
-#if HAVE_LITTLE_ENDIAN
-	return le_val;
-#else
-	return bswap_64(le_val);
-#endif
+	return LE64_TO_CPU_CONST(le_val);
 }
 
 /**
@@ -126,11 +245,7 @@ static inline uint64_t le64_to_cpu(uint64_t le_val)
  */
 static inline uint32_t le32_to_cpu(uint32_t le_val)
 {
-#if HAVE_LITTLE_ENDIAN
-	return le_val;
-#else
-	return bswap_32(le_val);
-#endif
+	return LE32_TO_CPU_CONST(le_val);
 }
 
 /**
@@ -139,11 +254,7 @@ static inline uint32_t le32_to_cpu(uint32_t le_val)
  */
 static inline uint16_t le16_to_cpu(uint16_t le_val)
 {
-#if HAVE_LITTLE_ENDIAN
-	return le_val;
-#else
-	return bswap_16(le_val);
-#endif
+	return LE16_TO_CPU_CONST(le_val);
 }
 
 /**
@@ -152,11 +263,7 @@ static inline uint16_t le16_to_cpu(uint16_t le_val)
  */
 static inline uint64_t cpu_to_be64(uint64_t native)
 {
-#if HAVE_LITTLE_ENDIAN
-	return bswap_64(native);
-#else
-	return native;
-#endif
+	return CPU_TO_BE64_CONST(native);
 }
 
 /**
@@ -165,11 +272,7 @@ static inline uint64_t cpu_to_be64(uint64_t native)
  */
 static inline uint32_t cpu_to_be32(uint32_t native)
 {
-#if HAVE_LITTLE_ENDIAN
-	return bswap_32(native);
-#else
-	return native;
-#endif
+	return CPU_TO_BE32_CONST(native);
 }
 
 /**
@@ -178,11 +281,7 @@ static inline uint32_t cpu_to_be32(uint32_t native)
  */
 static inline uint16_t cpu_to_be16(uint16_t native)
 {
-#if HAVE_LITTLE_ENDIAN
-	return bswap_16(native);
-#else
-	return native;
-#endif
+	return CPU_TO_BE16_CONST(native);
 }
 
 /**
@@ -191,11 +290,7 @@ static inline uint16_t cpu_to_be16(uint16_t native)
  */
 static inline uint64_t be64_to_cpu(uint64_t be_val)
 {
-#if HAVE_LITTLE_ENDIAN
-	return bswap_64(be_val);
-#else
-	return be_val;
-#endif
+	return BE64_TO_CPU_CONST(be_val);
 }
 
 /**
@@ -204,11 +299,7 @@ static inline uint64_t be64_to_cpu(uint64_t be_val)
  */
 static inline uint32_t be32_to_cpu(uint32_t be_val)
 {
-#if HAVE_LITTLE_ENDIAN
-	return bswap_32(be_val);
-#else
-	return be_val;
-#endif
+	return BE32_TO_CPU_CONST(be_val);
 }
 
 /**
@@ -217,11 +308,7 @@ static inline uint32_t be32_to_cpu(uint32_t be_val)
  */
 static inline uint16_t be16_to_cpu(uint16_t be_val)
 {
-#if HAVE_LITTLE_ENDIAN
-	return bswap_16(be_val);
-#else
-	return be_val;
-#endif
+	return BE16_TO_CPU_CONST(be_val);
 }
 
 #endif /* CCAN_ENDIAN_H */

ccan/endian/test/compile_ok-constant.c

+#include <ccan/endian/endian.h>
+
+struct foo {
+	char one[BSWAP_16_CONST(0xFF00)];
+	char two[BSWAP_32_CONST(0xFF000000)];
+	char three[BSWAP_64_CONST(0xFF00000000000000ULL)];
+};
+
+int main(void)
+{
+	return 0;
+}