Perform unaligned writes via FFI when necessary #587
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Bodigrim
reviewed
May 21, 2023
cpp-options: -Werror=undef is pulling its weight already.
|
Ah, right. Of course Omitting the C functions when we don't actually use them on the Haskell side seems to be more trouble than it's worth. |
This reverts commit 145cdac.
- Haskell unaligned write functions now live in a new module:
Data.ByteString.Utils.UnalignedWrite
- The word*HexFixed functions now use unaligned writes;
likewise Data.ByteString.Builder.RealFloat.Internal.copyWord16.
- An FFI workaround for unaligned Float/Double writes was added.
- The data tables in Data.ByteString.Builder.Prim.Internal.Base16
and Data.ByteString.Builder.RealFloat.{D,F}2S now live in
the new file cbits/aligned-static-hs-data.c so that we can
fearlessly perform aligned reads from them.
- The static Word64 data tables are now stored in
host-byte-order instead of always little-endian.
- Data.ByteString.Builder.RealFloat.Internal.digit_table
is now a static data blob instead of a CAF.
- All CPP around castFloatToWord32/castDoubleToWord64 now
lives in Data.ByteString.Builder.Prim.Internal.Floating.
clyring
commented
Sep 15, 2023
| @@ -124,24 +125,27 @@ library | |||
| NamedFieldPuns | |||
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|
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| ghc-options: -Wall -fwarn-tabs -Wincomplete-uni-patterns | |||
| -optP -Wall -optP -Werror=undef | |||
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-optP -Werror=undef instead of -Wcpp-undef is another sacrifice to ghc-8.0 compatibility.
Bodigrim
reviewed
Sep 15, 2023
| W64# (indexWord64OffAddr# arr i) | ||
| #endif | ||
| getWord64At :: Ptr Word64 -> Int -> Word64 | ||
| getWord64At (Ptr arr) (I# i) = W64# (indexWord64OffAddr# arr i) |
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Why is it sufficient now, without byteSwap64#?
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Nevermind, it's because lookup tables now automatically have correct endianness.
Bodigrim
approved these changes
Sep 15, 2023
clyring
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to clyring/bytestring
that referenced
this pull request
Jan 30, 2024
It is poorly documented and dangerous with respect to alignment and internal padding. It is exposed only via the semi-internal module Data.ByteString.Builder.Prim.Internal, and has no users on Hackage. (Since haskell#587 we do not use it internally.)
Merged
Bodigrim
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Jan 30, 2024
It is poorly documented and dangerous with respect to alignment and internal padding. It is exposed only via the semi-internal module Data.ByteString.Builder.Prim.Internal, and has no users on Hackage. (Since #587 we do not use it internally.)
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As noted in #184: We also perform (un-guarded) unaligned
Word16writes when performing fixed-width hexadecimal encoding, but this doesn't seem to be causing any actual problems.Perhaps this patch should be more liberal about unaligned
Word16writes. I'd like to take a closer look at that before merging this.