bit: Add bswap() overloads for every primitive type

Fixes: #145

src/bit.h

@@ -198,15 +198,35 @@ static inline uint8_t bswap_u8(uint8_t n) {
 	return n;
 }
 
-/**
- * Reverse the byte order of an integer.
- */
-#define bswap(n) \
-	_Generic((n), \
-		uint8_t: bswap_u8, \
-		uint16_t: bswap_u16, \
-		uint32_t: bswap_u32, \
-		uint64_t: bswap_u64)(n)
+#if UCHAR_WIDTH == 8
+#  define bswap_uc bswap_u8
+#endif
+
+#if USHRT_WIDTH == 16
+#  define bswap_us bswap_u16
+#elif USHRT_WIDTH == 32
+#  define bswap_us bswap_u32
+#elif USHRT_WIDTH == 64
+#  define bswap_us bswap_u64
+#endif
+
+#if UINT_WIDTH == 16
+#  define bswap_ui bswap_u16
+#elif UINT_WIDTH == 32
+#  define bswap_ui bswap_u32
+#elif UINT_WIDTH == 64
+#  define bswap_ui bswap_u64
+#endif
+
+#if ULONG_WIDTH == 32
+#  define bswap_ul bswap_u32
+#elif ULONG_WIDTH == 64
+#  define bswap_ul bswap_u64
+#endif
+
+#if ULLONG_WIDTH == 64
+#  define bswap_ull bswap_u64
+#endif
 
 // Define an overload for each unsigned type
 #define UINT_OVERLOADS(macro) \
@@ -225,6 +245,11 @@ static inline uint8_t bswap_u8(uint8_t n) {
 		unsigned long:      name##_ul, \
 		unsigned long long: name##_ull)
 
+/**
+ * Reverse the byte order of an integer.
+ */
+#define bswap(n) UINT_SELECT(n, bswap)(n)
+
 // C23 polyfill: bit utilities
 
 #if __STDC_VERSION_STDBIT_H__ >= C23

tests/bit.c

@@ -81,6 +81,13 @@ void check_bit(void) {
 	check_eq(bswap((uint32_t)0x12345678), 0x78563412);
 	check_eq(bswap((uint64_t)0x1234567812345678), 0x7856341278563412);
 
+	// Make sure we can bswap() every unsigned type
+	(void)bswap((unsigned char)0);
+	(void)bswap((unsigned short)0);
+	(void)bswap(0U);
+	(void)bswap(0UL);
+	(void)bswap(0ULL);
+
 	check_eq(count_ones(0x0U), 0);
 	check_eq(count_ones(0x1U), 1);
 	check_eq(count_ones(0x2U), 1);