Add function byteSwap by Priyansh121096 · Pull Request #55211 · ClickHouse/ClickHouse

Priyansh121096 · 2023-10-02T22:38:32Z

Fixes #54734.

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New Feature

Changelog entry (a user-readable short description of the changes that goes to CHANGELOG.md):

Added function byteSwap which reverses the bytes of unsigned integers. This is particularly useful for reversing values of types which are represented as unsigned integers internally such as IPv4.

Documentation entry for user-facing changes

Documentation is written (mandatory for new features)

Information about CI checks: https://clickhouse.com/docs/en/development/continuous-integration/

byteSwap accepts an integer `operand` and returns the integer which is obtained by swapping the **endianness** of `operand` i.e. reversing the bytes of the `operand`. Issue: ClickHouse#54734

UInt[8|16|32|64] TODOs: - Improve NOT_IMPLEMENTED error message. - Add implementation for FixedStrings (reverse the bytes). - See whether this needs to be implemented for UInt[128|256] and signed integers as well.

CLAassistant · 2023-10-02T22:38:37Z

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Priyansh121096 · 2023-10-02T22:54:46Z

Hello, I've added an implementation for the byteSwap function asked for in #54734. The example given in the issue works with this implementation:

┌─toIPv4(3351772109)─┐
│ 199.199.251.205    │
└────────────────────┘

┌─toIPv4(byteSwap(3351772109))─┐
│ 205.251.199.199              │
└──────────────────────────────┘

I have the following queries with regards to this feature:

I have currently implemented byteSwap for UInt[8|16|32|64] types.
a. Do we want to implement it for UInt[128|256] as well? There's no __builtin_bswap[128|256] available in clang but we can add our custom implementation if required.
b. Do we want to implement it for any other data types (Int*, FixedString, etc.)?
As per this, conversion between numeric types and IPv6 is not allowed. This means that even though byteSwap can work with UInt128 (which is how IPv6s are represented internally - ref), one cannot use the results of byteSwap to reverse IPv6s in the same way as one can with IPv4s. What should we do about this?
Can this function be considered "injective"? IIUC, if a function is injective, no two distinct inputs lead to the same output. While that seems to be the case here, I'm confused as to whether we consider a function injective across data types or not. For example, byteSwap(0xFF00) == 0xFF == byteSwap(0xFF). I would think that since the two byteSwaps produce values of different data types (UInt16 and UInt8 respectively), they can be considered distinct even though their "value" is the same. Could someone please advise?

Priyansh121096 · 2023-10-06T19:40:53Z

src/Functions/byteSwap.cpp

+template <typename T>
+inline T byteSwap(T)
+{
+    throw Exception(ErrorCodes::NOT_IMPLEMENTED, "byteSwap() is not implemented for {} datatype", demangle(typeid(T).name()));


Right now for anything greater than or equal to 2^64, this prints the following error:

SELECT byteSwap(18446744073709552000.) Query id: 7e644036-8f5a-42ac-be5e-ee1f2286c46e 0 rows in set. Elapsed: 0.005 sec. Received exception from server (version 23.9.1): Code: 48. DB::Exception: Received from localhost:9000. DB::Exception: byteSwap() is not implemented for double datatype: While processing byteSwap(18446744073709552000.). (NOT_IMPLEMENTED)

I'd love to know if there's a way to get better type names.

Here's my attempt at an implementation for UInt128:

template <typename T> requires std::is_same_v<T, UInt128> inline T byteSwap(T x) { UInt64 lower_half = x & 0xFFFFFFFFFFFFFFFF; UInt64 upper_half = (x >> 64) & 0xFFFFFFFFFFFFFFFF; UInt64 swapped_lower_half = __builtin_bswap64(lower_half); UInt64 swapped_upper_half = __builtin_bswap64(upper_half); UInt128 new_upper_half = static_cast<UInt128> (swapped_lower_half) << 64; UInt128 new_lower_half = static_cast<UInt128> (swapped_upper_half); return new_upper_half | new_lower_half; }

But I'm not able to test the same. As soon as I go over (2^64-1), for some reason, it doesn't reach the implementation. Also notice that the last four digits of the input change (1616 -> 2000.). Any reasons why this could be happening?

clickhouse-400817.internal :) SELECT byteSwap(18446744073709551616); SELECT byteSwap(18446744073709552000.) Query id: 0743873e-f48b-423f-a160-1b160f5b25c3 0 rows in set. Elapsed: 0.125 sec. Received exception from server (version 23.9.1): Code: 48. DB::Exception: Received from localhost:9000. DB::Exception: byteSwap() is not implemented for double datatype: While processing byteSwap(18446744073709552000.). (NOT_IMPLEMENTED)

But I'm not able to test the same. As soon as I go over (2^64-1), for some reason, it doesn't reach the implementation. Also notice that the last four digits of the input change (1616 -> 2000.). Any reasons why this could be happening?

Because the example is interpreted as float:

SELECT toTypeName(18446744073709551616); ┌─toTypeName(18446744073709552000.)─┐ │ Float64 │ └───────────────────────────────────┘

Try: SELECT byteSwap(18446744073709551616::UInt128);

I wonder why byteSwap on UInt64 and UInt128 operates on 2x8, respectively 4x8 bytes instead of 1x16 / 1x32 bytes? To swap all bytes uniformly, you could use reverseMemcpy() (base/base/unaligned.h).

src/Functions/byteSwap.cpp

robot-ch-test-poll4 · 2023-10-07T22:26:47Z

This is an automated comment for commit b7936cb with description of existing statuses. It's updated for the latest CI running

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tests/queries/0_stateless/02415_all_new_functions_must_be_documented.reference

alexey-milovidov · 2023-10-07T22:36:39Z

Do we want to implement it for UInt[128|256] as well?

Let's try.

Can this function be considered "injective"? IIUC, if a function is injective, no two distinct inputs lead to the same output. While that seems to be the case here, I'm confused as to whether we consider a function injective across data types or not.

It's ok to make this function considered injective. The injectiveness property is used to eliminate function application, e.g. from GROUP BY. It means that only the domain of one data type is relevant.

- Consider byteswap injective. - Make function case-insensitive. - Add in-code documentation and copy-paste it to the markdown docs.

- Also allow signed ints now because std::byteswap accepts them. - Fix for style check.

…unctions

docs/en/sql-reference/functions/math-functions.md

tests/queries/0_stateless/02887_byteswap.sql

Also: - Add comments in tests. - Add an example in docs where an IPv4 is casted to an int, byteswapped and then casted back to an IPv4.

src/Functions/byteSwap.cpp

Co-authored-by: Priyansh Agrawal <agrawal.priyansh@yahoo.in>

Priyansh121096 · 2023-10-13T17:27:10Z

@rschu1ze @alexey-milovidov, thanks for the merge! Hoping to make many more contributions in the future.

Priyansh121096 added 3 commits September 24, 2023 21:02

Add function byteSwap.

f27a76b

byteSwap accepts an integer `operand` and returns the integer which is obtained by swapping the **endianness** of `operand` i.e. reversing the bytes of the `operand`. Issue: ClickHouse#54734

Implement byteswap for following dtypes.

46fbe00

UInt[8|16|32|64] TODOs: - Improve NOT_IMPLEMENTED error message. - Add implementation for FixedStrings (reverse the bytes). - See whether this needs to be implemented for UInt[128|256] and signed integers as well.

Docs and comment

540d966

Priyansh121096 mentioned this pull request Oct 2, 2023

Function byteSwap #54734

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Priyansh121096 added 2 commits October 6, 2023 19:32

Add tests

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Priyansh121096 marked this pull request as ready for review October 6, 2023 19:36

Priyansh121096 commented Oct 6, 2023

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alexey-milovidov added the can be tested Allows running workflows for external contributors label Oct 7, 2023

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Priyansh121096 added 2 commits October 7, 2023 23:05

Address a few review comments.

302291e

- Consider byteswap injective. - Make function case-insensitive. - Add in-code documentation and copy-paste it to the markdown docs.

Use std::byteswap instead of custom implementations.

2c04370

- Also allow signed ints now because std::byteswap accepts them. - Fix for style check.

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Priyansh121096 requested a review from alexey-milovidov October 8, 2023 02:14

byteSwap is now documented; remove it from the list of undocumented f…

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…unctions

rschu1ze reviewed Oct 9, 2023

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Priyansh121096 added 2 commits October 9, 2023 21:16

Remove "unsigned" from docs now that we support all ints.

2e4709f

Add negative tests.

9677ded

Also: - Add comments in tests. - Add an example in docs where an IPv4 is casted to an int, byteswapped and then casted back to an IPv4.

Priyansh121096 requested a review from rschu1ze October 9, 2023 21:54

Some fixups

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rschu1ze and others added 2 commits October 10, 2023 23:45

Update src/Functions/byteSwap.cpp

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Co-authored-by: Priyansh Agrawal <agrawal.priyansh@yahoo.in>

Update src/Functions/byteSwap.cpp

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Co-authored-by: Priyansh Agrawal <agrawal.priyansh@yahoo.in>

alexey-milovidov assigned rschu1ze Oct 12, 2023

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rschu1ze merged commit d02a718 into ClickHouse:master Oct 13, 2023

rschu1ze mentioned this pull request Oct 13, 2023

byteswap: Add 16/32-byte integer support #55607

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Add function byteSwap#55211

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