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  # Test for features which may not be available at compile time

     

       
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  preBuild = ''

     

       
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    # Use pread(), pread64(), pwrite(), pwrite64() functions for better performance if they are available.

     

       
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    if cc -Werror=implicit-function-declaration -x c - -o "$TMPDIR/pread_pwrite_test" <<< \

     

       
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      ''$'#include <unistd.h>\nint main()\n{\n  pread(0, NULL, 0, 0);\n  pwrite(0, NULL, 0, 0);\n  return 0;\n}'; then

     

       
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      export NIX_CFLAGS_COMPILE="$NIX_CFLAGS_COMPILE -DUSE_PREAD"

     

       
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    fi

     

       
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    if cc -Werror=implicit-function-declaration -x c - -o "$TMPDIR/pread64_pwrite64_test" <<< \

     

       
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      ''$'#include <unistd.h>\nint main()\n{\n  pread64(0, NULL, 0, 0);\n  pwrite64(0, NULL, 0, 0);\n  return 0;\n}'; then

     

       
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      export NIX_CFLAGS_COMPILE="$NIX_CFLAGS_COMPILE -DUSE_PREAD64"

     

       
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    elif cc -D_LARGEFILE64_SOURCE -Werror=implicit-function-declaration -x c - -o "$TMPDIR/pread64_pwrite64_test" <<< \

     

       
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      ''$'#include <unistd.h>\nint main()\n{\n  pread64(0, NULL, 0, 0);\n  pwrite64(0, NULL, 0, 0);\n  return 0;\n}'; then

     

       
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      export NIX_CFLAGS_COMPILE="$NIX_CFLAGS_COMPILE -DUSE_PREAD64 -D_LARGEFILE64_SOURCE"

     

       
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    fi

     

       
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    # Necessary for FTS5 on Linux

     

       
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    export NIX_CFLAGS_LINK="$NIX_CFLAGS_LINK -lm"

     

       
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