System.Xml.Xsl.XPathConvert.BigInteger.Subtract C# (CSharp) Méthode

            public void Subtract(BigInteger bi) {
                AssertValid();
                bi.AssertValid();
                Debug.Assert((object)this != (object)bi);

                int idx;
                uint wCarry, uT;

                if (length < bi.length) {
                    goto LNegative;
                }

                wCarry = 1;
                for (idx = 0; idx < bi.length; idx++) {
                    Debug.Assert(0 == wCarry || 1 == wCarry);
                    uT = bi.digits[idx];

                    // NOTE: We should really do:
                    //    wCarry = AddU(ref digits[idx], wCarry);
                    //    wCarry += AddU(ref digits[idx], ~uT);
                    // The only case where this is different than
                    //    wCarry = AddU(ref digits[idx], ~uT + wCarry);
                    // is when 0 == uT and 1 == wCarry, in which case we don't
                    // need to add anything and wCarry should still be 1, so we can
                    // just skip the operations.

                    if (0 != uT || 0 == wCarry) {
                        wCarry = AddU(ref digits[idx], ~uT + wCarry);
                    }
                }
                while (0 == wCarry && idx < length) {
                    wCarry = AddU(ref digits[idx], 0xFFFFFFFF);
                }

                if (0 != wCarry) {
                    if (idx == length) {
                        // Trim off zeros.
                        while (--idx >= 0 && 0 == digits[idx]) {
                        }
                        length = idx + 1;
                    }
                    AssertValid();
                    return;
                }

            LNegative:
                // bi was bigger than this.
                Debug.Assert(false, "Who's subtracting to negative?");
                length = 0;
                AssertValid();
            }