Using assembly language, it is possible to take the absolute value of a register in just three instructions (example shown for a 32-bit register on an x86 architecture, Intel syntax):
http://www.google.fr/#hl=fr&q=%22absolute+value%22+algorithm&meta=&fp=1&cad=b
http://www.experiencefestival.com/a/Absolute_value_-_Algorithms/id/604651
cdq
xor eax, edx
sub eax, edx
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