How to calculate gdp of a company during promotion and loss?
As noted in a comment, GDP is associated with a country, not a firm.

But if we are talking about the contribution to GDP, the operating assumption is that calculations are based on observed (market) prices. So the value of consumption is \$100 if we are calculating GDP based on expenditures. If we are looking at domestic income, it would be \$100: \$200 wage income, and -\$100 business income. 

Statisticians do not attempt to decide what goods are “really worth”, they use data based on actual transactions. Since GDP numbers are estimates based on a variety of sources, it is unlikely that they capture when particular firms have promotional sales.