• Bit: The smallest unit in computers. It is either a 1 or a 0.
• Nibble: Half a byte, or 4 bites.
• Byte: 8 bits together form one byte, a number from 0 to 255. Bits in the byte are numbered starting from the right at 0.
• Short: Two bytes put together is 16 bits, forming a number from 0 to 65535. The low byte is the rightmost eight bits.
• Hex Number: A HEX number consisting of 4 numbers is 16-bit.

## Finger Counting PinkyRingMiddleIndexThumb
Value124816

Finger binary is a system for counting and displaying binary numbers on the fingers of one or more hands. It is possible to count from 0 to 31 using the fingers of a single hand. In the binary number system, each numerical digit has two possible states(0 or 1) and each successive digit represents an increasing power of two.

For example, the number 10 is expressed by folding the index and ring finger, the number 20 is expressed by folding the thumb and the middle finger.

## Conversion

Break down the binary value in chunks of 4, multiply each 1 by its equivalent value, either 8, 4, 2 or 1. Add the resulting numbers together to get the result. For example, the value 1100, or (8*1 + 4*1), is equal to C(decimal 12).

`1101 0101(D5)`
11010101Binary
1286432168421Values
128641641Result: 213

## Arithmetic

In the first column, divide the first number by 2 by removing the last bit, until 1 is reached. In the second column, multiply by 2 by adding an extra bit of 0. The answer is found by adding the numbers in the second column with odd numbers in the first column. A binary number ending with 1 is odd.

This example multiplies 35 by 19, to arrive at a result of 665. The result `1010011001` can be deconstucted as:

`10 1001 1001 = 1 + 8 + 16 + 128 + 512 = 665`
3519
`100011`` 10011`
` 10001`` 100110`
` 1000`` 1001100`
` 100`` 10011000`
` 10`` 100110000`
` 1``1001100000`
`1010011001`

Multiplication

Binary numbers are easy to multiply and divide by multiples of 2. Rotate one bit left to multiply by 2, and rotates one bit right to divide by 2.

 22 44 `ROL` 11 `ROR` 0 0 0 1 0 1 1 0 0 0 1 0 1 1 0 0 0 0 0 0 1 0 1 1

## Logic

AND, or "both", sets individual bits to 0. AND is useful for masking bits, for example, to mask the high order bits of a value AND with \$0F: \$36 AND \$0F = \$06. ORA(OR), or "either one or both", sets individual bits to 1. OR is useful for setting a particular bit, for example, \$80 OR \$08 = \$88. EOR(XOR), or "one or the other but not both", inverts individual bits.

 input output AND ORA EOR 0 1 0 1 1 0 0 0 0 0 1 1 1 1 0 1 0 0 1 1

## Toggling Bits

To activate the 1st, 2nd and 4th bits:

 0 0 0 0 1 0 1 1
```unsigned char num = 0;
num |= (1 << 0);
num |= (1 << 1);
num |= (1 << 3);
```

To deactivate the 1st, 4th and 6th bits:

 1 1 0 1 0 1 1 0
```unsigned char num = 255;
num &= ~(1 << 0);
num &= ~(1 << 3);
num &= ~(1 << 5);
```

`(num >> bit) & 1;`

## Signed Integers

If Bit 7 is not set (as in the first example) the representation of signed and unsigned numbers is the same. However, when Bit 7 is set, the number is always negative. For this reason Bit 7 is sometimes called the sign bit.

 Binary Unsigned Signed 0010 0011 35 35 1010 0011 163 -93 1111 1111 255 -1 1000 0000 128 -128

## Fixed Point

A fixed-point number is a number that has a fixed number of digits after the decimal point. If, for example, we use 8 bits to store a number with decimal points, we could decide to store it this way. The high and low nibbles have the same resolution.

Integer PartDecimal Points
000000000.0
001110103.a
010001014.5

### Conversion

To turn a regular integer into fixed point, shift left by the number of fractional bits(width << bits), and to turn a fixed point into integer, shift right by the number of fractional bits(width >> bits).

### Multiplication

To multiply, you do the multiply, and then you shift right by the number of fractional bits.

`(3.8 * 2.0) >> 8`

### Division

To divide, you first shift the numerator left by the number of fractional bits, then you do the division.

`(3.8 << 8) / 2.0`