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    SubjectRe: [PATCH 1/3] futex: remove duplicated code
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    On 03/04/17 05:05, Russell King - ARM Linux wrote:
    >>
    >> +static int futex_atomic_op_inuser(int encoded_op, u32 __user *uaddr)
    >> +{
    >> + int op = (encoded_op >> 28) & 7;
    >> + int cmp = (encoded_op >> 24) & 15;
    >> + int oparg = (encoded_op << 8) >> 20;
    >> + int cmparg = (encoded_op << 20) >> 20;
    >
    > Hmm. oparg and cmparg look like they're doing these shifts to get sign
    > extension of the 12-bit values by assuming that "int" is 32-bit -
    > probably worth a comment, or for safety, they should be "s32" so it's
    > not dependent on the bit-width of "int".
    >

    For readability, perhaps we should make sign- and zero-extension an
    explicit facility?

    /*
    * Truncate an integer x to n bits, using sign- or
    * zero-extension, respectively.
    */
    static inline __const_func__ s32 sex32(s32 x, int n)
    {
    return (x << (32-n)) >> (32-n);
    }

    static inline __const_func__ s64 sex64(s64 x, int n)
    {
    return (x << (64-n)) >> (64-n);
    }

    #define sex(x,y) \
    ((__typeof__(x)) \
    (((__builtin_constant_p(y) && ((y) <= 32)) || \
    (sizeof(x) <= sizeof(s32))) \
    ? sex32((x),(y)) : sex64((x),(y))))

    static inline __const_func__ u32 zex32(u32 x, int n)
    {
    return (x << (32-n)) >> (32-n);
    }

    static inline __const_func__ u64 zex64(u64 x, int n)
    {
    return (x << (64-n)) >> (64-n);
    }

    #define zex(x,y) \
    ((__typeof__(x)) \
    (((__builtin_constant_p(y) && ((y) <= 32)) || \
    (sizeof(x) <= sizeof(u32))) \
    ? zex32((x),(y)) : zex64((x),(y))))

    \
     
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