Signed Binary to Integer: Number 1000 1111 Converted and Written as a Base Ten Integer, in Decimal System

Signed binary number 1000 1111(2) written as a base ten integer, in decimal system

1. Is this a positive or a negative number?

1000 1111 is the binary representation of a negative integer, on 8 bits.


In a signed binary, the first bit (the leftmost) is reserved for the sign,

1 = negative, 0 = positive. This bit does not count when calculating the absolute value.


2. Construct the unsigned binary number.

Exclude the first bit (the leftmost), that is reserved for the sign:

1000 1111 = 000 1111


3. Map the unsigned binary number's digits versus the corresponding powers of 2 that their place value represent:

  • 26

    0

  • 25

    0

  • 24

    0

  • 23

    1

  • 22

    1

  • 21

    1

  • 20

    1

4. Multiply each bit by its corresponding power of 2 and add all the terms up.

000 1111(2) =

(0 × 26 + 0 × 25 + 0 × 24 + 1 × 23 + 1 × 22 + 1 × 21 + 1 × 20)(10) =

(0 + 0 + 0 + 8 + 4 + 2 + 1)(10) =

(8 + 4 + 2 + 1)(10) =

15(10)

5. If needed, adjust the sign of the integer number by the first digit (leftmost) of the signed binary:

1000 1111(2) = -15(10)

The number 1000 1111(2) converted from a signed binary (base two) and written as an integer in decimal system (base ten):
1000 1111(2) = -15(10)

Spaces were used to group digits: for binary, by 4, for decimal, by 3.

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How to convert signed binary numbers from binary system to decimal (base ten)

To understand how to convert a signed binary number from binary system to decimal (base ten), the easiest way is to do it through an example - convert the binary number, 1001 1110, to base ten:

  • In a signed binary, the first bit (leftmost) is reserved for the sign, 1 = negative, 0 = positive. This bit does not count when calculating the absolute value (value without sign). The first bit is 1, so our number is negative.
  • Write bellow the binary number in base two, and above each bit that makes up the binary number write the corresponding power of 2 (numeral base) that its place value represents, starting with zero, from the right of the number (rightmost bit), walking to the left of the number and increasing each corresonding power of 2 by exactly one unit, but ignoring the very first bit (the leftmost, the one representing the sign):
  • powers of 2:   6 5 4 3 2 1 0
    digits: 1 0 0 1 1 1 1 0
  • Build the representation of the positive number in base 10, by taking each digit of the binary number, multiplying it by the corresponding power of 2 and then adding all the terms up, but also taking care of the number sign:

    1001 1110 =

    - (0 × 26 + 0 × 25 + 1 × 24 + 1 × 23 + 1 × 22 + 1 × 21 + 0 × 20)(10) =

    - (0 + 0 + 16 + 8 + 4 + 2 + 0)(10) =

    - (16 + 8 + 4 + 2)(10) =

    -30(10)

  • Binary signed number, 1001 1110 = -30(10), signed negative integer in base 10