--- a/hotspot/src/share/vm/code/compressedStream.hpp Wed Jun 28 19:12:58 2017 -0400
+++ b/hotspot/src/share/vm/code/compressedStream.hpp Thu Jun 29 14:22:42 2017 +0200
@@ -66,7 +66,40 @@
private:
inline u_char read() { return _buffer[_position++]; }
- jint read_int_mb(jint b0); // UNSIGNED5 coding, 2-5 byte cases
+ // This encoding, called UNSIGNED5, is taken from J2SE Pack200.
+ // It assumes that most values have lots of leading zeroes.
+ // Very small values, in the range [0..191], code in one byte.
+ // Any 32-bit value (including negatives) can be coded, in
+ // up to five bytes. The grammar is:
+ // low_byte = [0..191]
+ // high_byte = [192..255]
+ // any_byte = low_byte | high_byte
+ // coding = low_byte
+ // | high_byte low_byte
+ // | high_byte high_byte low_byte
+ // | high_byte high_byte high_byte low_byte
+ // | high_byte high_byte high_byte high_byte any_byte
+ // Each high_byte contributes six bits of payload.
+ // The encoding is one-to-one (except for integer overflow)
+ // and easy to parse and unparse.
+
+ jint read_int_mb(jint b0) {
+ int pos = position() - 1;
+ u_char* buf = buffer() + pos;
+ assert(buf[0] == b0 && b0 >= L, "correctly called");
+ jint sum = b0;
+ // must collect more bytes: b[1]...b[4]
+ int lg_H_i = lg_H;
+ for (int i = 0; ; ) {
+ jint b_i = buf[++i]; // b_i = read(); ++i;
+ sum += b_i << lg_H_i; // sum += b[i]*(64**i)
+ if (b_i < L || i == MAX_i) {
+ set_position(pos+i+1);
+ return sum;
+ }
+ lg_H_i += lg_H;
+ }
+ }
public:
CompressedReadStream(u_char* buffer, int position = 0)