LEB128

LEB128 or Little Endian Base 128 is a variable-length encoding of integers - that is, it aims to store integers of different sizes efficiently. It is used in the DWARF debug information format, Web Assembly, and other formats and protocols. This Raku module provides both encoding and decoding.

Encoding

There are both signed and unsigned encoding functions, encode-leb128-signed and encode-leb128-unsigned respectively. Both are multis with candidates that take an Int and return a Buf with the encoded value:

my $buf-eu = encode-leb128-unsigned(1234);
my $buf-es = encode-leb128-signed(-1234);

Or to write the encoded Int into a Buf and return the number of bytes written, which is often more efficient since it avoids the creation of a temporary Buf:

my $buf = Buf.new;
my $offset = 0;
$offset += encode-leb128-unsigned(1234, $buf, $offset);

Decoding

There are both signed and unsigned decoding functions, decode-leb128-signed and decode-leb128-unsigned respectively. Both are multis with candidates that take a Buf and try to decode an Int from the start of it, returning that Int:

my $value-du = decode-leb128-unsigned($entire-buffer-u);
my $value-ds = decode-leb128-signed($entire-buffer-s);

Or that decode the value from a specified offset in a given buffer, and use an rw parameter of type int, which is incremented by the number of bytes consumed.

my int $read;
my $value = decode-leb128-unsigned($buffer, $offset, $read);

To have the offset updated, it may be passed as both parameters:

my $value = decode-leb128-unsigned($buffer, $offset, $offset);