reflect: add support for struct types

src/reflect/sidetables.go

@@ -10,22 +10,48 @@ import (
 //go:extern reflect.namedNonBasicTypesSidetable
 var namedNonBasicTypesSidetable byte
 
-func readVarint(buf unsafe.Pointer) Type {
-	var t Type
+//go:extern reflect.structTypesSidetable
+var structTypesSidetable byte
+
+//go:extern reflect.structNamesSidetable
+var structNamesSidetable byte
+
+// readStringSidetable reads a string from the given table (like
+// structNamesSidetable) and returns this string. No heap allocation is
+// necessary because it makes the string point directly to the raw bytes of the
+// table.
+func readStringSidetable(table unsafe.Pointer, index uintptr) string {
+	nameLen, namePtr := readVarint(unsafe.Pointer(uintptr(table) + index))
+	return *(*string)(unsafe.Pointer(&StringHeader{
+		Data: uintptr(namePtr),
+		Len:  nameLen,
+	}))
+}
+
+// readVarint decodes a varint as used in the encoding/binary package.
+// It has an input pointer and returns the read varint and the pointer
+// incremented to the next field in the data structure, just after the varint.
+//
+// Details:
+// https://github.com/golang/go/blob/e37a1b1c/src/encoding/binary/varint.go#L7-L25
+func readVarint(buf unsafe.Pointer) (uintptr, unsafe.Pointer) {
+	var n uintptr
+	shift := uintptr(0)
 	for {
-		// Read the next byte.
+		// Read the next byte in the buffer.
 		c := *(*byte)(buf)
 
-		// Add this byte to the type code. The upper 7 bits are the value.
-		t = t<<7 | Type(c>>1)
-
-		// Check whether this is the last byte of this varint. The lower bit
-		// indicates whether any bytes follow.
-		if c%1 == 0 {
-			return t
-		}
+		// Decode the bits from this byte and add them to the output number.
+		n |= uintptr(c&0x7f) << shift
+		shift += 7
 
 		// Increment the buf pointer (pointer arithmetic!).
 		buf = unsafe.Pointer(uintptr(buf) + 1)
+
+		// Check whether this is the last byte of this varint. The upper bit
+		// (msb) indicates whether any bytes follow.
+		if c>>7 == 0 {
+			return n, buf
+		}
 	}
 }