Instead of lengthy blurbs, switch to single-line, machine-readable
standardized (https://spdx.dev) license identifiers. The Linux kernel
switched long ago, so there is strong precedent.
Three cases are handled: AGPL-only, Apache-only, and dual licensed.
For the latter case, I chose (AGPL-3.0-or-later and Apache-2.0),
reasoning that our changes are extensive enough to apply our license.
The changes we applied mechanically with a script, except to
licenses/README.md.
Closes#9937
Standard encoding is compiled into a loop that puts values
into memory byte-by-byte. This works slowly, but reliably.
When allocating an object LSA uses ubel64 encoder with 2
features that allow to optimize the encoder:
1. the value is migrator.index() which is small enough
to fit 2 bytes when encoded
2. After the descriptor there usually comes an object
which is of 8+ bytes in size
Feature #1 makes it possible to encode the value with just
a few instructions. In O3 level clang makes it like
mov %esi,%ecx
and $0xfc0,%ecx
and $0x3f,%esi
lea (%rsi,%rcx,4),%ecx
add $0x40,%ecx
Next, the encoder needs to put the value into a gap whose
size depends on the alignment of previous and current objects,
so the classical algo loops through this size. Feature #2
makes it possible to put the encoded value and the needed
amount of zeros by using 2 64-bit movs. In this case the
encoded value gets off the needed size and overwrites some
memory after. That's OK, as this overwritten memory is where
the allocated object _will_ be, so the contents there is not
of any interest.
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
The LSA code encodes an object descriptor before the object
itself. The descriptor is 32-bit value and to put it in an
efficient manner it's encoded into unsigned little-endian
base-64 sequence.
The encoding code is going to be optimized, so put it into a
dedicated header in advance.
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
