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Diffstat (limited to 'doc')
| -rw-r--r-- | doc/specs/thrift-compact-protocol.md | 18 |
1 files changed, 15 insertions, 3 deletions
diff --git a/doc/specs/thrift-compact-protocol.md b/doc/specs/thrift-compact-protocol.md index 001bb1229..89301eb5d 100644 --- a/doc/specs/thrift-compact-protocol.md +++ b/doc/specs/thrift-compact-protocol.md @@ -61,9 +61,21 @@ def longToZigZag(n: Long): Long = (n << 1) ^ (n >> 63) def zigzagToLong(n: Long): Long = (n >>> 1) ^ - (n & 1) ``` -The zigzag int is then encoded as a *var int*. Var ints take 1 to 5 bytes (int32) or 1 to 10 bytes (int64). The most -significant bit of each byte indicates if more bytes follow. The concatenation of the least significant 7 bits from each -byte form the number, where the first byte has the most significant bits (so they are in big endian or network order). +The zigzag int is then encoded as a *var int*, also known as *Unsigned LEB128*. Var ints take 1 to 5 bytes (int32) or +1 to 10 bytes (int64). The process consists in taking a Big Endian unsigned integer, left-padding the bit-string to +make it a multiple of 7 bits, splitting it into 7-bit groups, prefixing the most-significant 7-bit group with the 0 +bit, prefixing the remaining 7-bit groups with the 1 bit and encoding the resulting bit-string in Little Endian. + +For example, the integer 50399 is encoded as follows: + +``` +50399 = 1100 0100 1101 1111 (Big Endian representation) + = 00000 1100 0100 1101 1111 (Left-padding) + = 0000011 0001001 1011111 (7-bit groups) + = 00000011 10001001 11011111 (Most-significant bit prefixes) + = 11011111 10001001 00000011 (Little Endian representation) + = 0xDF 0x89 0x03 +``` Var ints are sometimes used directly inside the compact protocol to represent positive numbers. |