Lua numbers in Tarantool
Igor MunkinProblem #1
tarantool> 2^52 == 2^52 + 0.5
–––
- <result>
...
Problem #1
tarantool> 2^52 == 2^52 + 0.5
–––
- true
...
Problem #1
tarantool> 2^52 == 2^52 + 0.5
–––
- true
...
tarantool> 2^52 == 2^52 + 1
–––
- <result>
...
Problem #1
tarantool> 2^52 == 2^52 + 0.5
–––
- true
...
tarantool> 2^52 == 2^52 + 1
–––
- false
...
Problem #1
tarantool> 2^52 == 2^52 + 0.5
–––
- true
...
tarantool> 2^52 == 2^52 + 1
–––
- false
...
tarantool> 2^53 == 2^53 + 1
–––
- <result>
...
Problem #1
tarantool> 2^52 == 2^52 + 0.5
–––
- true
...
tarantool> 2^52 == 2^52 + 1
–––
- false
...
tarantool> 2^53 == 2^53 + 1
–––
- true
...
Problem #1
tarantool> 2^52 == 2^52 + 0.5
–––
- true
...
tarantool> 2^52 == 2^52 + 1
–––
- false
...
tarantool> 2^53 == 2^53 + 1
–––
- true
...
tarantool> 2^53 == 2^53 + 2
–––
- <result>
...
Problem #1
tarantool> 2^52 == 2^52 + 0.5
–––
- true
...
tarantool> 2^52 == 2^52 + 1
–––
- false
...
tarantool> 2^53 == 2^53 + 1
–––
- true
...
tarantool> 2^53 == 2^53 + 2
–––
- false
...
Effect #1.1
tarantool> box.cfg{} <snip> box.space.s:create_index('i')
–––
- <snip>
...
Effect #1.1
tarantool> box.cfg{} <snip> box.space.s:create_index('i')
–––
- <snip>
...
tarantool> box.space.s:insert({2^53})
–––
- <result>
...
Effect #1.1
tarantool> box.cfg{} <snip> box.space.s:create_index('i')
–––
- <snip>
...
tarantool> box.space.s:insert({2^53})
–––
- [9007199254740992]
...
Effect #1.1
tarantool> box.cfg{} <snip> box.space.s:create_index('i')
–––
- <snip>
...
tarantool> box.space.s:insert({2^53})
–––
- [9007199254740992]
...
tarantool> box.space.s:insert({2^53 + 1})
–––
- <result>
...
Effect #1.1
tarantool> box.cfg{} <snip> box.space.s:create_index('i')
–––
- <snip>
...
tarantool> box.space.s:insert({2^53})
–––
- [9007199254740992]
...
tarantool> box.space.s:insert({2^53 + 1})
–––
- error: Duplicate key exists in unique index 'i' in space 's'
...
Effect #1.2
tarantool> box.space.s:select({2^53})
–––
- <result>
...
Effect #1.2
tarantool> box.space.s:select({2^53})
–––
- [9007199254740992]
...
Effect #1.2
tarantool> box.space.s:select({2^53})
–––
- [9007199254740992]
...
tarantool> box.space.s:select({2^53 + 1})
–––
- <result>
...
Effect #1.2
tarantool> box.space.s:select({2^53})
–––
- [9007199254740992]
...
tarantool> box.space.s:select({2^53 + 1})
–––
- [9007199254740992]
...
WAT #1
tarantool> type(box.space.s:select({2^53})[1])
–––
- <result>
...
WAT #1
tarantool> type(box.space.s:select({2^53})[1])
–––
- cdata
...
WAT #1
Workaround #1
tarantool> 9007199254740992ULL
–––
- <result>
...
Workaround #1
tarantool> 9007199254740992ULL
–––
- 9007199254740992
...
Workaround #1
tarantool> 9007199254740992ULL
–––
- 9007199254740992
...
tarantool> type(9007199254740992ULL)
–––
- <result>
...
Workaround #1
tarantool> 9007199254740992ULL
–––
- 9007199254740992
...
tarantool> type(9007199254740992ULL)
–––
- cdata
...
Workaround #1
tarantool> 9007199254740992ULL
–––
- 9007199254740992
...
tarantool> type(9007199254740992ULL)
–––
- cdata
...
tarantool> 9007199254740992ULL + 1
–––
- <result>
...
Workaround #1
tarantool> 9007199254740992ULL
–––
- 9007199254740992
...
tarantool> type(9007199254740992ULL)
–––
- cdata
...
tarantool> 9007199254740992ULL + 1
–––
- 9007199254740993
...
Workaround #1
tarantool> 9007199254740992ULL + 1
–––
- 9007199254740993
...
tarantool> 9007199254740992ULL == 9007199254740992ULL + 1
–––
- <result>
...
Workaround #1
tarantool> 9007199254740992ULL + 1
–––
- 9007199254740993
...
tarantool> 9007199254740992ULL == 9007199254740992ULL + 1
–––
- false
...
Workaround #1
tarantool> 9007199254740992ULL + 1
–––
- 9007199254740993
...
tarantool> 9007199254740992ULL == 9007199254740992ULL + 1
–––
- false
...
tarantool> 9007199254740992ULL == 9007199254740992ULL + 0.5
–––
- <result>
...
Workaround #1 (?)
tarantool> 9007199254740992ULL + 1
–––
- 9007199254740993
...
tarantool> 9007199254740992ULL == 9007199254740992ULL + 1
–––
- false
...
tarantool> 9007199254740992ULL == 9007199254740992ULL + 0.5
–––
- true
...
Workaround #1 (?)
tarantool> 9007199254740992ULL == 9007199254740992ULL + 1
–––
- false
...
tarantool> 9007199254740992ULL == 9007199254740992ULL + 0.5
–––
- true
...
tarantool> 9007199254740992ULL + 0.5
–––
- 9007199254740992
...
Problem #2
tarantool> 9007199254740992ULL < 9007199254740992ULL + 1
–––
- <result>
...
Problem #2
tarantool> 9007199254740992ULL < 9007199254740992ULL + 1
–––
- true
...
Problem #2
tarantool> 9007199254740992ULL < 9007199254740992ULL + 1
–––
- true
...
tarantool> 9007199254740992ULL < -1
–––
- <result>
...
Problem #2
tarantool> 9007199254740992ULL < 9007199254740992ULL + 1
–––
- true
...
tarantool> 9007199254740992ULL < -1
–––
- true
...
Effect #2
tarantool> box.cfg{listen = 3313} <snip> c = nb.connect(box.cfg.listen)
<snip>
–––
...
Effect #2
tarantool> box.cfg{listen = 3313} <snip> c = nb.connect(box.cfg.listen)
<snip>
–––
...
tarantool> t = {} for _ = 1, 10 do
> table.insert(t,
> c:execute('SELECT random()').rows[1]
> :totable()[1]
> )
> end
–––
...
Effect #2
tarantool> box.cfg{listen = 3313} <snip> c = nb.connect(box.cfg.listen)
<snip>
–––
...
tarantool> t = {} for _ = 1, 10 do
> table.insert(t,
> c:execute('SELECT random()').rows[1]
> :totable()[1]
> )
> end
–––
...
tarantool> table.sort(t)
–––
...
Effect #2
tarantool> t
–––
- <result>
...
Effect #2
tarantool> t
–––
- - 1064442337705904389
- 5430535088656468933
- 8084626668617668138
- -7957167126669429942
- -6755436305203424895
- -6476727283901405634
- -5944830508420504980
- -2428743323307643782
- -1162597621816885600
- -108704732427766924
...
Long story short
-
Native Lua numeric type
- Lack of precision for several groups of numbers
-
FFI cdata numeric types
- 64-bit integer promotion and cast rules according to C standard
Odd arithmetics for both existing numeric types
Bonus tracks
Lua numbers in Tarantool Igor Munkin
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