# Converting a number to 16-bit Floating Point Format

I want to convert the number -29.375 to IEEE 745 16-bit floating point format. Here is my solution:

The format of the floating point number is: 1 sign bit unbiased exponent in 4 bits plus a sign bit 10 bits for the mantissa plus the explicit 1

First, I realize that 29.375 = 29 + 3/8.
Then realize that:
29 = 16 +13 = 16 + 8 + 5 = 16 + 8 + 4 + 1 1 1101.011 = 1.1101 0110 * 2^3

This gives us:
mantissa is: 1101 011000
sign: 1
exp: 00011

Hence in 16 bits, we have: 1000111101011000

Do I have this right? I was hoping that there would be a calculator on the web that I could use but I could not find one. They were all at least 32-bits.

First of all, the IEEE 745 16-bit format has:

• 1 bit for the sign.
• 5 bits (not 4) for the biased exponent. The bias is $$15$$.
• 10 bits for the mantissa. The leading $$1$$ is implicit (not explicit).

The calculation is incorrect since $$(29.375)_2 = (11101.011)_2 = (1.1101011)_2 \cdot 2^4$$ (and not $$2^3$$).

Then:

• The sign bit is $$1$$ because the number is negative.
• The unbiased exponent is $$(4)_{10} = (100)_{2}$$ and therefore the biased exponent is $$(19)_{10} = (10011)_2$$.
• The mantissa, without the implicit leading $$1$$ and padded to 10 bits with trailing zeros, is $$(1101011000)_2$$.

Then the final $$16$$-bit number is: $$1100111101011000$$.

• The problem was to convert -29.375 to IEEE 745 format. That is, the number is negative.
– Bob
Commented Apr 28, 2020 at 12:04
• Ooops sorry! I edited my answer. Everything stays the same except for the first bit. Commented Apr 28, 2020 at 13:02