double-double/src/basic/fast-two-diff.ts

Pure double-double precision functions *with strict error bounds*.

/**
 * Returns the difference and exact error of subtracting two floating point 
 * numbers. 
 * Uses an EFT (error-free transformation), i.e. `a-b === x+y` exactly.
 * The returned result is a non-overlapping expansion (smallest value first!).
 * 
 * * **precondition:** `abs(a) >= abs(b)` - A fast test that can be used is 
 * `(a > b) === (a > -b)`
 * 
 * See https://people.eecs.berkeley.edu/~jrs/papers/robustr.pdf
 */
function fastTwoDiff(a: number, b: number) {
    const x = a - b;
    const y = (a - x) - b;

    return [y, x];
}


export { fastTwoDiff }