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Re: naked switches

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Tim Rentsch <tr.17687@z991.linuxsc.com> writes:
>Ben Bacarisse <ben.usenet@bsb.me.uk> writes:
>
>> David Brown <david.brown@hesbynett.no> writes:
>>
>>> Your extension [for extracting contiguous bits from a word] is not
>>> commonly used, because it only exists in your tool.  People who need
>>> to do a lot of bit slicing and don't like masking and shifting (or
>>> struct bit-fields) should not have trouble defining:
>>>
>>> #define BIT(x, top, bottom) \
>>> 	(((x) >> (bottom)) & ((1llu << ((top) - (bottom) + 1)) - 1))
>>>
>>> Yes, the parenthesis you need for macros are ugly, but you only need to
>>> get it right once, and now you can read your bit-fields.
>>
>> That's undefined when all the bits are wanted.  (The left shift of 1llu
>> could be equal to the width.)  Maybe you wrote it for a compiler that
>> documents an extension.
>>
>> I usually right shift -1llu by the width minus the number of bits
>> wanted, but you can also just do two left shifts.
>
>Another way, assuming the mask width desired is greater
>than zero, is this
>
>    ((1LLU << width-1) -1) *2 +1
>
>which works great if 'width' is a compile-time constant.

In the C++ world, we use this:

namespace bit
{
    template <class T> static inline T maskT(size_t bits)
    {
        if (bits >= sizeof(T)*8)
            return -1;
        else
            return ~(static_cast<T>(-1)<<bits);
    }

    template<class T> static inline T extract(T input, size_t stop_bit, size_t start_bit)
    {
        input >>= start_bit;
        input &= maskT<T>(stop_bit - start_bit + 1);
        return input;
    }

    static inline int64_t extracts(uint64_t input, size_t stop_bit, size_t start_bit)
    {
        int64_t imm = extract(input, stop_bit, start_bit);
        int shift = 63-stop_bit+start_bit;
        imm <<= shift;
        imm >>= shift;
        return imm;
    }

    template<class T> static inline T insert(T original, uint64_t insert, size_t start_bit, size_t width_bits)
    {
        T mask = bit::maskT<T>(width_bits);
        T newdata = mask & insert;
        mask <<= start_bit;
        newdata <<= start_bit;
        original &= ~mask;
        original |= newdata;
        return original;
    }
};

    uint64_t registervalue, field;
     int64_t field1;

    field = bit::extract(registervalue, 15, 0);      /* Extract <15:0> and zero-extend */
    field1 = bit::extracts((int64_t)registervalue, 20, 16);   /* Extract and sign-extend */

    registervalue = bit::insert(registervalue, 0xff, 16, 4); /* Set bits<19:16> == 0xff */

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naked switches Robert Finch <robfi680@gmail.com> - 2021-07-07 16:39 -0700
  Re: naked switches Bart <bc@freeuk.com> - 2021-07-08 01:26 +0100
  Re: naked switches Kaz Kylheku <563-365-8930@kylheku.com> - 2021-07-08 01:57 +0000
    Re: naked switches David Brown <david.brown@hesbynett.no> - 2021-07-08 09:16 +0200
  Re: naked switches Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-07-08 01:00 -0700
    Re: naked switches Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2021-07-08 03:25 -0700
      Re: naked switches Robert Finch <robfi680@gmail.com> - 2021-07-08 06:58 -0700
        Re: naked switches Bart <bc@freeuk.com> - 2021-07-08 15:52 +0100
        Re: naked switches David Brown <david.brown@hesbynett.no> - 2021-07-08 17:52 +0200
          Re: naked switches Bart <bc@freeuk.com> - 2021-07-08 17:51 +0100
            Re: naked switches David Brown <david.brown@hesbynett.no> - 2021-07-09 10:01 +0200
              Re: naked switches Bart <bc@freeuk.com> - 2021-07-09 11:09 +0100
                Re: naked switches David Brown <david.brown@hesbynett.no> - 2021-07-09 13:14 +0200
                Re: naked switches Manfred <noname@add.invalid> - 2021-07-09 15:35 +0200
                Re: naked switches David Brown <david.brown@hesbynett.no> - 2021-07-09 16:51 +0200
                Re: naked switches Manfred <noname@add.invalid> - 2021-07-09 18:23 +0200
                Re: naked switches Bart <bc@freeuk.com> - 2021-07-09 16:07 +0100
                Re: naked switches Manfred <noname@add.invalid> - 2021-07-09 18:41 +0200
                Re: naked switches David Brown <david.brown@hesbynett.no> - 2021-07-10 11:02 +0200
                Re: naked switches David Brown <david.brown@hesbynett.no> - 2021-07-09 19:20 +0200
                Re: naked switches Robert Finch <robfi680@gmail.com> - 2021-07-09 10:46 -0700
                Re: naked switches Kaz Kylheku <563-365-8930@kylheku.com> - 2021-07-09 19:56 +0000
                Re: naked switches Bart <bc@freeuk.com> - 2021-07-09 22:01 +0100
                Re: naked switches Robert Finch <robfi680@gmail.com> - 2021-07-09 15:07 -0700
                Re: naked switches Bart <bc@freeuk.com> - 2021-07-09 23:30 +0100
                Re: naked switches David Brown <david.brown@hesbynett.no> - 2021-07-10 12:17 +0200
          Re: naked switches Robert Finch <robfi680@gmail.com> - 2021-07-08 10:18 -0700
            Re: naked switches Bart <bc@freeuk.com> - 2021-07-08 18:43 +0100
              Re: naked switches Robert Finch <robfi680@gmail.com> - 2021-07-08 15:32 -0700
            Re: naked switches Kaz Kylheku <563-365-8930@kylheku.com> - 2021-07-08 17:47 +0000
              Re: naked switches Robert Finch <robfi680@gmail.com> - 2021-07-08 15:45 -0700
                Re: naked switches David Brown <david.brown@hesbynett.no> - 2021-07-09 10:27 +0200
                Re: naked switches Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-07-09 11:13 +0100
                Re: naked switches David Brown <david.brown@hesbynett.no> - 2021-07-09 13:30 +0200
                Re: naked switches Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-07-11 00:39 -0700
                Re: naked switches scott@slp53.sl.home (Scott Lurndal) - 2021-07-11 14:06 +0000
                Re: naked switches Robert Finch <robfi680@gmail.com> - 2021-07-11 08:01 -0700
                Re: naked switches Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-07-16 03:53 -0700
                Re: naked switches scott@slp53.sl.home (Scott Lurndal) - 2021-07-16 14:47 +0000
                Re: naked switches Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-09-30 06:09 -0700
                Re: naked switches Robert Finch <robfi680@gmail.com> - 2021-09-30 07:03 -0700
                Re: naked switches Bart <bc@freeuk.com> - 2021-07-09 13:44 +0100
                Re: naked switches David Brown <david.brown@hesbynett.no> - 2021-07-10 13:28 +0200
                Re: naked switches Bart <bc@freeuk.com> - 2021-07-10 13:04 +0100
                Re: naked switches David Brown <david.brown@hesbynett.no> - 2021-07-10 15:39 +0200
                Re: naked switches Bart <bc@freeuk.com> - 2021-07-10 15:08 +0100
                Re: naked switches David Brown <david.brown@hesbynett.no> - 2021-07-10 17:34 +0200
                Re: naked switches Bart <bc@freeuk.com> - 2021-07-10 17:47 +0100
              Re: naked switches Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-07-11 00:57 -0700
                Re: naked switches Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-07-16 03:51 -0700
        Re: naked switches Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-07-08 11:40 -0700
          Re: naked switches David Brown <david.brown@hesbynett.no> - 2021-07-09 10:38 +0200
  Re: naked switches Kaz Kylheku <563-365-8930@kylheku.com> - 2021-07-08 17:33 +0000
    Re: naked switches scott@slp53.sl.home (Scott Lurndal) - 2021-07-08 17:47 +0000
      Re: naked switches Kaz Kylheku <563-365-8930@kylheku.com> - 2021-07-08 17:58 +0000
        Re: naked switches scott@slp53.sl.home (Scott Lurndal) - 2021-07-08 19:13 +0000
          Re: naked switches Kaz Kylheku <563-365-8930@kylheku.com> - 2021-07-09 02:30 +0000
        Re: naked switches David Brown <david.brown@hesbynett.no> - 2021-07-09 10:41 +0200
  Re: naked switches Bonita Montero <Bonita.Montero@gmail.com> - 2021-09-30 18:04 +0200

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