That's where the expression in the return statement comes from. The result is then zero if the bit we're checking was zero, or non-zero if it was one. A byte can represent the equivalent of a single character, such as the letter B, a comma, or a percentage sign, or it can represent a number from 0 to 255. The single one bit in the mask will basically let the equivalent bit in the value flow through to the result. You can see that all the zero bits in the mask result in the equivalent result bits being zero. Starting at zero and going through 20, counting in decimal and binary looks like this: 0 0 1 1 2 10 3 11 4 100 5 101 6 110 7. That makes counting in binary pretty easy. You can see that in binary numbers, each bit holds the value of increasing powers of 2. What comes before a bit What comes after a bit Bits in a computer processor. Tip Because all information (even a single character) is larger than a bit a byte is the smallest unit of measurement to measure a file. Decimal BinaryĤ 0000 0100 (the bitmask for the third-from-least bit).Ġ000 0100 (the result of the AND operation). So: (1 23) + (0 22) + (1 21) + (1 20) 8 + 0 + 2 + 1 11. So, if you had two bytes ( word) it would be 16 bits (2 x 816), and 10 bytes would be 80 bits (10 x 880). ![]() Let's say you have the value 13 and you want to see if the third-from-least-significant bit is set. temp: BYTE temp AT temp : ARRAY0.7 OF BOOL tempX : BYTE tempX AT tempX : ARRAY0.7 OF BOOL tempL : BYTE tempL AT tempL : ARRAY0. The relevant table is: AND | 0 1įor a given char value, we use the single-bit bit masks to check if a bit is set. The AND operation & will set a bit in the target only if both bits are set in the tewo sources. The simplified AND-only version is below. That feels like a bit (ha) of a waste, and it is. C s normal storage options would mean devoting an entire char (8 bits) or int (16 bits) to keeping track of such tiny values. ![]() Now, unfortunately, you don't get a true or false value. When dealing with microcontrollers in particular, you will regularly have a small collection of sensors or switches that are providing on/off values. You use the AND against a bit pattern to see if that bit is set. For example, if the original byte has an even of 1s (with 9th bit at GND), the parity bit is set to 1 (from the EVEN output). 000100 - 000100 As you can see, you end up with a binary sequence, which is represented by 4 in decimal (base-10). In this case, the 9th input bit is connected to the 9th bit of memory. This circuit also checks EVEN or ODD parity for the 9-bit number. If you want to know how the bitwise operators work, see here. Typically, for generation, the 9th input bit is set to 0. The number one mantra in optimisation is "Measure, don't guess!" Just make sure you benchmark any solution you're given, including this one (a). And if you make it static and suggest inlining, or force it inline as a macro definition, you can even bypass the cost of a function call. Do not pass in an invalid n, that'll be undefined behaviour.Īt insane optimisation level -O3, gcc gives us: isNthBitSet: pushl %ebp No error checking is done since you cited speed as the most important consideration. If those assumption are incorrect, it simply comes down to expanding and/or re-ordering the mask array. This assumes 8-bit bytes (not a given in C) and the zeroth bit being the highest order one. Bytes will not be used to represent whether or not processes on a computer are running by flipping bits of the byte to 0 or 1, there are different mechanisms at play.The following function can do what you need: int isNthBitSet (unsigned char c, int n) One of the amazing properties of binary representation is how many different types of information can be represented by simple 0s and 1s.ĭo note, though, that on the machine itself processes have process IDs (PIDs) and their metadata is managed by the operating system. However, if you decided to formulate your own unique problem such that a byte represents processes which are on and off then it could be used in that manner (it makes for an intriguing thought experiment). Using the byte to represent whether a process is "On" or "Off" in process counts of 8 is not a conventional use that I have come across. A multitude of bytes can represent an image, a text file, a video file, etc. However, a byte (or a multitude of bytes) can represent different types of information depending on the context (as mentioned in the article). We also talk about them being true and false. Generally, we represent them with the numerals 1 and 0. ![]() A binary number is made up of elements called bits where each bit can be in one of the two possible states. A byte can represent a number using 8 binary digits 10110110 would be equivalent to the base-10 number 182 (if we are not considering two's complement representation) or -74 (if we are considering two's complement representation). Binary is a base-2 number system that uses two mutually exclusive states to represent information.
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