Extractor bit use9/8/2023 ![]() ![]() ![]() Currently, the following states regulate the offer and sale of franchises: California, Hawaii, Illinois, Indiana, Maryland, Michigan, Minnesota, New York, North Dakota, Oregon, Rhode Island, South Dakota, Virginia, Washington, and Wisconsin. An offer is made only by Franchise Disclosure Document (FDD). This information is not intended as an offer to sell, or the solicitation of an offer to buy, a franchise. Then you also don't need the assignarray function, and you'll use much less memory.Ranked by Entrepreneur Magazine, Tools Distribution Category years 2007, 2008, 2010, 2011, 2012. b# and not being able to use a variable, you can just define the union as flags32 and omit the rest of the struct. The union itself is only 4 bytes, but since you can't do pointers to bit-fields (without complicated and debatably "non-standard" code), then the array makes a copy of each boolean value and uses a full byte for each one, instead of just the bit, so it takes up 9x the total memory space (if you run the printf statement examples I gave, you'll see).īut now, you can address each bit one-by-one and use a variable to index each one, which is great if you're not short on memory.īy using the typedefs above and the assignarray function as a constructor for flags32, you can easily expand to multiple variables. The issue with this last example is that it's not compact. Printf("%lu\n", sizeof(bitmaster.number)) Struct flags32 assignarray ( unsigned long thisnumber ) If there's a reason you may need to vary which bits you're looking at to anything, you could use a struct with an array that keeps a copy of the bits like so: #include The caveat here is this works if you always want the same set of bits over and over. So most of these could have been just unsigned int and some even could be unsigned short I made all of the variables type unsigned long but you can use any variable type as long as the number of bits doesn't exceed those that can be used in the type. You can set the struct bit-fields up for whatever bits you want to get. I gave two examples kind of randomly assigned different bits to show. If you want the second 4 bits: second4bits = 4 If you want the last 8 bits: last16bits = 8 Then you can access the bits you want from any number you assign to the member mynumber: myunion getmybits Now you can set up your union: typedef union myunion If you have multiple bit patterns, you can even use that in your union as well. You can set that struct up to whatever bit pattern you want. You can use a union of an integer type that has enough bits for your application and a bit field struct. I have another method for accomplishing this. There is a special cpu instruction BLSMSK that helps to compute the mask ((1 << n) - 1). If the offset is always zero as in all your examples in the question then you don't need the more general getbits(). Unsigned last16bitsvalue = value & ((1u << 16) - 1) // & 0xffff I presume I am supposed to use the modulus operator and I tried it and was able to get the last 8 bits and last 16 bits unsigned last8bitsvalue = value & ((1u << 8) - 1) // & 0xff Return 0 /* value is padded with infinite zeros on the left */Ĭonst unsigned mask = (1u << n) - 1 /* n '1's */įor example, to get 3 bits from 2273 ( 0b100011100001) starting at 5-th bit, call getbits(2273, 5, 3)-it extracts 7 ( 0b111).įor example, say I want the first 17 bits of the 32-bit value what is it that I should do? unsigned first_bits = value & ((1u << 17) - 1) // & 0x1ffffĪssuming CHAR_BIT * sizeof(unsigned) is 32 on your system. Unsigned getbits(unsigned value, unsigned offset, unsigned n)Ĭonst unsigned max_n = CHAR_BIT * sizeof(unsigned) There are intrinsic functions such as _bextr_u32() (link requires sign-in) that allow to invoke this instruction explicitly. There is a single BEXTR (Bit field extract (with register)) x86 instruction on Intel and AMD CPUs and UBFX on ARM. ![]()
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