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Move all endianness/byte-order CPP into one module (#659)
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{-# LANGUAGE CPP #-} | ||
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-- | Why does this module exist? There is "GHC.ByteOrder" in base. | ||
-- But that module is /broken/ until base-4.14/ghc-8.10, so we | ||
-- can't rely on it until we drop support for older ghcs. | ||
-- See https://gitlab.haskell.org/ghc/ghc/-/issues/20338 | ||
-- and https://gitlab.haskell.org/ghc/ghc/-/issues/18445 | ||
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#include "MachDeps.h" | ||
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module Data.ByteString.Utils.ByteOrder | ||
( ByteOrder(..) | ||
, hostByteOrder | ||
, whenLittleEndian | ||
, whenBigEndian | ||
) where | ||
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data ByteOrder | ||
= LittleEndian | ||
| BigEndian | ||
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hostByteOrder :: ByteOrder | ||
hostByteOrder = | ||
#ifdef WORDS_BIGENDIAN | ||
BigEndian | ||
#else | ||
LittleEndian | ||
#endif | ||
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-- | If the host is little-endian, applies the given function to the given arg. | ||
-- If the host is big-endian, returns the second argument unchanged. | ||
whenLittleEndian :: (a -> a) -> a -> a | ||
whenLittleEndian fun val = case hostByteOrder of | ||
LittleEndian -> fun val | ||
BigEndian -> val | ||
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-- | If the host is little-endian, returns the second argument unchanged. | ||
-- If the host is big-endian, applies the given function to the given arg. | ||
whenBigEndian :: (a -> a) -> a -> a | ||
whenBigEndian fun val = case hostByteOrder of | ||
LittleEndian -> val | ||
BigEndian -> fun val |
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