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Question

The 32-bit IEEE 754 single precision representation of a number is 0xC2710000. The number in decimal representation is ________. (rounded off to two decimal places)

The question asks to convert the 32-bit IEEE 754 single-precision hexadecimal representation $0xC2710000$ into its decimal equivalent.

Step 1: Convert Hexadecimal to Binary

First, convert the hexadecimal number $0xC2710000$ into its 32-bit binary representation:

  • $C$ = $1100$
  • $2$ = $0010$
  • $7$ = $0111$
  • $1$ = $0001$
  • $0$ = $0000$

Combining these, the 32-bit binary representation is:

$11000010011100010000000000000000$

Step 2: Identify IEEE 754 Components

For a 32-bit single-precision float, the structure is:

  • Sign bit: 1 bit (the most significant bit)
  • Exponent bits: 8 bits
  • Mantissa bits: 23 bits

Breaking down the binary representation:

  • Sign bit (S): $1$
  • Exponent bits (E): $10000100$
  • Mantissa bits (M): $11100010000000000000000$

Step 3: Interpret the Sign Bit

The sign bit is $1$, which indicates that the number is negative.

Step 4: Interpret the Exponent Bits

The exponent bits are $10000100$.

  • Convert this binary exponent to decimal: $(1 \times 2^7) + (0 \times 2^6) + (0 \times 2^5) + (0 \times 2^4) + (0 \times 2^3) + (1 \times 2^2) + (0 \times 2^1) + (0 \times 2^0) = 128 + 0 + 0 + 0 + 0 + 4 + 0 + 0 = 132$
  • The bias for single-precision floats is 127. Subtract the bias to find the actual exponent value (e): $e = 132 - 127 = 5$

Step 5: Interpret the Mantissa Bits

The mantissa bits are $11100010000000000000000$.

  • For normalized numbers (which this is, as the exponent is not all zeros or all ones), there is an implicit leading $1$ before the binary point. The value is represented as $1.M$.
  • The binary value is $1.11100010000000000000000_2$.
  • Convert the fractional part to decimal: $(1 \times 2^{-1}) + (1 \times 2^{-2}) + (1 \times 2^{-3}) + (0 \times 2^{-4}) + \dots + (1 \times 2^{-7}) + \dots$ $= 0.5 + 0.25 + 0.125 + 0 + \dots + (1/128) + \dots$ $= 0.875 + 0.0078125 = 0.8828125$
  • The value represented by the mantissa is $1 + 0.8828125 = 1.8828125$.

Step 6: Calculate the Decimal Value

The formula for the decimal value is $(-1)^S \times (\text{mantissa value}) \times 2^e$.

  • Substitute the values: $(-1)^1 \times 1.8828125 \times 2^5$ $= -1 \times 1.8828125 \times 32$ $= -60.25$

The number in decimal representation is $-60.25$. This is already rounded to two decimal places.

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Important Questions from Number Representation

  1. Which of the following pairs of octal and binary numbers are NOT equal?

  2. The greatest negative number which can be stored in a 8-bit register using 2's complement arithmetic is

  3. Which of the following codes is also known as reflected binary code?

  4. What is the octal equivalent of (F3B1)16?

  5. The 1's complement of binary number 10010 is

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