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Decimal Adjust after Subtraction                 Flags:  O D I T S Z A P C
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Syntax:  DAS                                             ?       ± ± ± ± ±
 
  Adjusts the result of a subtraction to a packed BCD number (less than
  100 decimal). The previous subtraction instruction should place its
  8-bit binary result in AL. DAS converts this binary sum to packed BCD
  format with the least significant decimal digit in the lower four bits
  and the most significant digit in the upper four bits. If the sum is
  greater than 99h after adjustment, then the carry and auxiliary carry
  flags are set. Otherwise, carry and auxiliary carry flags are cleared.
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