Add byteswap macros and self tests

- DUK_BSWAP32() and DUK_BSWAP16() in duk_features.h so that platform specific
  macros, intrinsics, or inline assembly can be used if necessary
- DUK_DBLUNION_BSWAP() for byte swapping doubles (needed by debugger)
- duk_byteswap_bytes() helper for byte swapping arbitrary data (needed by
  debugger for pointers)

src/duk_dblunion.h.in

@@ -309,4 +309,31 @@ typedef union duk_double_union duk_double_union;
 	} while (0)
 #endif  /* DUK_USE_PACKED_TVAL */
 
+/* Byteswap an (aligned) duk_double_union. */
+#if defined(DUK_USE_DOUBLE_LE)
+#define DUK_DBLUNION_BSWAP(u) do { \
+		duk_uint32_t duk__bswaptmp1, duk__bswaptmp2; \
+		duk__bswaptmp1 = (u)->ui[0]; \
+		duk__bswaptmp2 = (u)->ui[1]; \
+		duk__bswaptmp1 = DUK_BSWAP32(duk__bswaptmp1); \
+		duk__bswaptmp2 = DUK_BSWAP32(duk__bswaptmp2); \
+		(u)->ui[0] = duk__bswaptmp2; \
+		(u)->ui[1] = duk__bswaptmp1; \
+	} while (0)
+#elif defined(DUK_USE_DOUBLE_ME)
+#define DUK_DBLUNION_BSWAP(u) do { \
+		duk_uint32_t duk__bswaptmp1, duk__bswaptmp2; \
+		duk__bswaptmp1 = (u)->ui[0]; \
+		duk__bswaptmp2 = (u)->ui[1]; \
+		duk__bswaptmp1 = DUK_BSWAP32(duk__bswaptmp1); \
+		duk__bswaptmp2 = DUK_BSWAP32(duk__bswaptmp2); \
+		(u)->ui[0] = duk__bswaptmp1; \
+		(u)->ui[1] = duk__bswaptmp2; \
+	} while (0)
+#elif defined(DUK_USE_DOUBLE_BE)
+#define DUK_DBLUNION_BSWAP(u) do { } while (0)
+#else
+#error internal error, double endianness insane
+#endif
+
 #endif  /* DUK_DBLUNION_H_INCLUDED */

src/duk_features.h.in

@@ -2067,6 +2067,23 @@ typedef FILE duk_file;
 #define DUK_FUNC_MACRO  "unknown"
 #endif
 
+/*
+ *  Byteswap macros
+ *
+ *  These are here so that inline assembly or other platform functions can be
+ *  used if available.
+ */
+
+#define DUK_BSWAP32(x) \
+	((((duk_uint32_t) (x)) >> 24) | \
+	 ((((duk_uint32_t) (x)) >> 8) & 0xff00UL) | \
+	 ((((duk_uint32_t) (x)) << 8) & 0xff0000UL) | \
+	 (((duk_uint32_t) (x)) << 24))
+
+#define DUK_BSWAP16(x) \
+	((duk_uint16_t) (x) >> 8) | \
+	((duk_uint16_t) (x) << 8)
+
 /*
  *  Architecture string, human readable value exposed in Duktape.env
  */

src/duk_selftest.c

@@ -134,6 +134,55 @@ DUK_LOCAL void duk__selftest_byte_order(void) {
 	}
 }
 
+/*
+ *  DUK_BSWAP macros
+ */
+
+DUK_LOCAL void duk__selftest_bswap_macros(void) {
+	duk_uint32_t x32;
+	duk_uint16_t x16;
+	duk_double_union du;
+	duk_double_t du_diff;
+
+	x16 = 0xbeefUL;
+	x16 = DUK_BSWAP16(x16);
+	if (x16 != (duk_uint16_t) 0xefbeUL) {
+		DUK_PANIC(DUK_ERR_INTERNAL_ERROR, "self test failed: DUK_BSWAP16");
+	}
+
+	x32 = 0xdeadbeefUL;
+	x32 = DUK_BSWAP32(x32);
+	if (x32 != (duk_uint32_t) 0xefbeaddeUL) {
+		DUK_PANIC(DUK_ERR_INTERNAL_ERROR, "self test failed: DUK_BSWAP32");
+	}
+
+	/* >>> struct.unpack('>d', '4000112233445566'.decode('hex'))
+	 * (2.008366013071895,)
+	 */
+
+	du.uc[0] = 0x40; du.uc[1] = 0x00; du.uc[2] = 0x11; du.uc[3] = 0x22;
+	du.uc[4] = 0x33; du.uc[5] = 0x44; du.uc[6] = 0x55; du.uc[7] = 0x66;
+	DUK_DBLUNION_BSWAP(&du);
+	du_diff = du.d - 2.008366013071895;
+#if 0
+	DUK_FPRINTF(DUK_STDERR, "du_diff: %lg\n", (double) du_diff);
+#endif
+	if (du_diff > 1e-15) {
+		/* Allow very small lenience because some compilers won't parse
+		 * exact IEEE double constants (happened in matrix testing with
+		 * Linux gcc-4.8 -m32 at least).
+		 */
+#if 0
+		DUK_FPRINTF(DUK_STDERR, "Result of DUK_DBLUNION_BSWAP: %02x %02x %02x %02x %02x %02x %02x %02x\n",
+		            (unsigned int) du.uc[0], (unsigned int) du.uc[1],
+		            (unsigned int) du.uc[2], (unsigned int) du.uc[3],
+		            (unsigned int) du.uc[4], (unsigned int) du.uc[5],
+		            (unsigned int) du.uc[6], (unsigned int) du.uc[7]);
+#endif
+		DUK_PANIC(DUK_ERR_INTERNAL_ERROR, "self test failed: DUK_DBLUNION_BSWAP");
+	}
+}
+
 /*
  *  Basic double / byte union memory layout.
  */
@@ -227,6 +276,7 @@ DUK_INTERNAL void duk_selftest_run_tests(void) {
 	duk__selftest_packed_tval();
 	duk__selftest_twos_complement();
 	duk__selftest_byte_order();
+	duk__selftest_bswap_macros();
 	duk__selftest_double_union_size();
 	duk__selftest_double_aliasing();
 	duk__selftest_double_zero_sign();

src/duk_util.h

@@ -67,4 +67,6 @@ DUK_INTERNAL_DECL void duk_be_finish(duk_bitencoder_ctx *ctx);
 DUK_INTERNAL_DECL duk_uint32_t duk_util_tinyrandom_get_bits(duk_hthread *thr, duk_small_int_t n);
 DUK_INTERNAL_DECL duk_double_t duk_util_tinyrandom_get_double(duk_hthread *thr);
 
+DUK_INTERNAL void duk_byteswap_bytes(duk_uint8_t *p, duk_small_uint_t len);
+
 #endif  /* DUK_UTIL_H_INCLUDED */

src/duk_util_misc.c

@@ -44,3 +44,22 @@ DUK_INTERNAL duk_int8_t duk_hex_dectab[256] = {
 	-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,  /* 0xe0-0xef */
 	-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1   /* 0xf0-0xff */
 };
+
+/*
+ *  Arbitrary byteswap for potentially unaligned values
+ *
+ *  Used to byteswap pointers e.g. in debugger code.
+ */
+
+DUK_INTERNAL void duk_byteswap_bytes(duk_uint8_t *p, duk_small_uint_t len) {
+	duk_uint8_t tmp;
+	duk_uint8_t *q = p + len - 1;
+
+	while (p - q < 0) {
+		tmp = *p;
+		*p = *q;
+		*q = tmp;
+		p++;
+		q--;
+	}
+}