ones-complement

问题 The ISO C standard allows three encoding methods for signed integers: two's complement, one's complement and sign/magnitude. What's an efficient or good way to detect the encoding at runtime (or some other time if there's a better solution)? I want to know this so I can optimise a bignum library for the different possibilities. I plan on calculating this and storing it in a variable each time the program runs so it doesn't have to be blindingly fast - I'm assuming the encoding won't change

问题 The ISO C standard allows three encoding methods for signed integers: two's complement, one's complement and sign/magnitude. What's an efficient or good way to detect the encoding at runtime (or some other time if there's a better solution)? I want to know this so I can optimise a bignum library for the different possibilities. I plan on calculating this and storing it in a variable each time the program runs so it doesn't have to be blindingly fast - I'm assuming the encoding won't change

问题 The ISO C standard allows three encoding methods for signed integers: two's complement, one's complement and sign/magnitude. What's an efficient or good way to detect the encoding at runtime (or some other time if there's a better solution)? I want to know this so I can optimise a bignum library for the different possibilities. I plan on calculating this and storing it in a variable each time the program runs so it doesn't have to be blindingly fast - I'm assuming the encoding won't change

来源： https://stackoverflow.com/questions/26871079/what-is-the-proper-way-to-construct-a-biginteger-from-an-implied-unsigned-hexade

来源： https://stackoverflow.com/questions/26871079/what-is-the-proper-way-to-construct-a-biginteger-from-an-implied-unsigned-hexade

问题 Bitwise operators ( ~ , & , | and ^ ) operate on the bitwise representation of their promoted operands. Can such operations cause undefined behavior? For example, the ~ operator is defined this way in the C Standard: 6.5.3.3 Unary arithmetic operators The result of the ~ operator is the bitwise complement of its (promoted) operand (that is, each bit in the result is set if and only if the corresponding bit in the converted operand is not set). The integer promotions are performed on the

问题 Is there an easy way to produce a one's complement in python? For instance, if you take the hex value 0x9E , I need to convert it to 0x61 . I need to swap the binary 1's for 0's and 0's for 1's. It feels like this should be simple. 回答1: Just use the XOR operator ^ against 0xFF: >>> hex(0x9E ^ 0xFF) '0x61' If you need to work with values larger than a byte, you could create the mask from the int.bit_length() method on your value: >>> value = 0x9E >>> mask = (1 << value.bit_length()) - 1 >>>

问题 I have just learnt that to get the formula to find the 1st Complement is -x = 2^n - x - 1 I have managed to apply it on a binary case: -00001100 (base 2) = 2^8 - 12 - 1 = 243 = 11110011 (1s) However, when I try to apply the same formula to a base 5 number, -1042 (base 4) = 5^4 - 1042 - 1 = 625 - 1042 - 1 = - 400 (which is not the answer) Can some one help me out here? Thanks 回答1: you cannot calculate any formula with numbers in 2 different bases, you have to use their decimal representation

问题 I get an warning here. The warning says 'integer conversion results in truncation'. It persists even if I remove the typecast(U16). typedef unsigned short U16; U16 mask; mask = ~(U16)(0x8000); How do I resolve this warning? I used the below code and removed the warning, but unsure if its the right way to do it. mask = (U16)(~(U32)(0x8000)); Thanks in advance! 回答1: C compilers don't like when you try to assign constant values into an L-value that's not big enough to hold them. I would guess

问题 In an answer, jww points out that 1's complement is still used in encoding vector instructions on intel architectures, and Ruslan clarifies that these instructions are being used more as auto-vectorization becomes common. Is there an advantage of 1's complement that causes it to continue to be used in these instructions, or is it simply being used for historical reasons? Quoting jww: From Intel® 64 and IA-32 Architectures Software Developer’s Manual 2A, page 3-8: 3.1.1.8 Description Section