Method and apparatus for compiling dependent subtraction operations on arithmetic intervals

Abstract

One embodiment of the present invention provides a system for compiling computer code to perform a subtraction operation between a first interval and a third interval to produce a resulting interval. The system operates by receiving source code within a compiler. The system next determines if a subtraction operation within the source code is a dependent subtraction operation, wherein the third interval is the sum of the first interval and a second interval. If so, the system produces executable code for the subtraction operation that computes a left endpoint for the resulting interval and a right endpoint for the resulting interval. If the left endpoint of the third interval is negative infinity, the left endpoint of the resulting interval is assigned to be negative infinity. Otherwise, the left endpoint of the resulting interval is computed by subtracting a left endpoint of the first interval from a left endpoint of the third interval using a floating-point arithmetic unit, and rounding down to a nearest smaller floating-point number. Similarly, if the right endpoint of the third interval is positive infinity, the right endpoint of the resulting interval is assigned to be positive infinity. Otherwise, the right endpoint of the resulting interval is computed by subtracting a right endpoint of the first interval from a right endpoint of the third interval using the floating-point arithmetic unit, and rounding up to a nearest larger floating-point number.