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Are there any semantics differences? Is one of them likely to be faster under specific circumstances?
926
If it is a subtract operation you invert the second operand and put a one on the carry in and feed it to the same adder. Whatever falls out falls out. If your logic has enough bits to hold the result then it all works, if you do not have enough room then you overflow.
Well, we can subtract by adding. First, we just need to replace each digit of the smaller number with 9 minus that digit, except the final digit gets replaced with 10 minus that digit. So 1066 becomes 9 minus 1, 9 minus 0, 9 minus 6, 10 minus 6. Adding that to 1492 gives 10,426.
Alternatively referred to as subtraction, subtract is a math operation that takes the value of one number from another number. An example of addition is 10 - 4 = 6. On a computer, you can subtract numbers using a calculator or spreadsheet program and the hyphen (-) or subtraction symbol.
If you have -x precomputed, then sub smth, x and add smth, -x are going to execute equally quickly.
Semantically, there will be a difference in terms of the flags state.
Consider doing 8-bit addition and subtraction:
0x01 - 0x01 = 0x00, CF = 0
0x01 + 0xFF = 0x00, CF = 1
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