added gu_out_u16be, gu_out_u64be and gu_out_f64be in libgu. The later is using gu_encode_double which is probably still wrong. Corrected gu_in_le and gu_in_f64be.

src/runtime/c/gu/bits.c

@@ -41,3 +41,31 @@ gu_decode_double(uint64_t u)
 	}
 	return sign ? copysign(ret, -1.0) : ret;
 }
+
+GU_INTERNAL uint64_t
+gu_encode_double(double d)
+{
+	int sign = (d < 0) ? 1 : 0;
+	int rawexp;
+	double mantissa;
+
+	switch (fpclassify(d)) {
+	case FP_NAN:
+		rawexp   = 0x7ff;
+		mantissa = 1;
+		break;
+	case FP_INFINITE:
+		rawexp   = 0x7ff;
+		mantissa = 0;
+		break;
+	default:
+		mantissa = frexp(d, &rawexp);
+		rawexp += 1075;
+	}
+
+    uint64_t u = (((uint64_t) sign) << 63) |
+                 ((((uint64_t) rawexp) << 52) & 0x7ff) |
+                 ((uint64_t) mantissa);
+
+	return u;
+}

src/runtime/c/gu/bits.h

@@ -144,6 +144,7 @@ gu_decode_2c64(uint64_t u, GuExn* err)
 GU_INTERNAL_DECL double
 gu_decode_double(uint64_t u);
 
-
+GU_INTERNAL_DECL uint64_t
+gu_encode_double(double d);
 
 #endif // GU_BITS_H_

src/runtime/c/gu/in.c

@@ -152,7 +152,7 @@ gu_in_le(GuIn* in, GuExn* err, int n)
 	uint8_t buf[8];
 	gu_in_bytes(in, buf, n, err);
 	uint64_t u = 0;
-	for (int i = 0; i < n; i++) {
+	for (int i = n-1; i >= 0; i--) {
 		u = u << 8 | buf[i];
 	}
 	return u;
@@ -246,7 +246,7 @@ gu_in_f64le(GuIn* in, GuExn* err)
 GU_API double
 gu_in_f64be(GuIn* in, GuExn* err)
 {
-	return gu_decode_double(gu_in_u64le(in, err));
+	return gu_decode_double(gu_in_u64be(in, err));
 }
 
 static void

src/runtime/c/gu/out.c

@@ -1,6 +1,7 @@
 #include <gu/seq.h>
 #include <gu/out.h>
 #include <gu/utf8.h>
+#include <gu/bits.h>
 #include <stdio.h>
 
 static bool
@@ -168,8 +169,31 @@ gu_out_is_buffered(GuOut* out);
 extern inline bool
 gu_out_try_u8_(GuOut* restrict out, uint8_t u);
 
+GU_API void
+gu_out_u16be(GuOut* out, uint16_t u, GuExn* err)
+{
+	gu_out_u8(out, (u>>8) && 0xFF, err);
+	gu_out_u8(out, u      && 0xFF, err);
+}
 
+GU_API void
+gu_out_u64be(GuOut* out, uint64_t u, GuExn* err)
+{
+	gu_out_u8(out, (u>>56) && 0xFF, err);
+	gu_out_u8(out, (u>>48) && 0xFF, err);
+	gu_out_u8(out, (u>>40) && 0xFF, err);
+	gu_out_u8(out, (u>>32) && 0xFF, err);
+	gu_out_u8(out, (u>>24) && 0xFF, err);
+	gu_out_u8(out, (u>>16) && 0xFF, err);
+	gu_out_u8(out, (u>>8)  && 0xFF, err);
+	gu_out_u8(out, u       && 0xFF, err);
+}
 
+GU_API void
+gu_out_f64be(GuOut* out, double d, GuExn* err)
+{
+	gu_out_u64be(out, gu_encode_double(d), err);
+}
 
 typedef struct GuBufferedOutStream GuBufferedOutStream;