- Add some big-integer algorithms.

[bigint/bigint.git] / BigUnsigned.cc

diff --git a/BigUnsigned.cc b/BigUnsigned.cc
index db407c5..9e5a347 100644 (file)
--- a/BigUnsigned.cc
+++ b/BigUnsigned.cc
@@ -625,8 +625,17 @@ void BigUnsigned::bitXor(const BigUnsigned &a, const BigUnsigned &b) {
        zapLeadingZeros();
 }
 
-void BigUnsigned::bitShiftLeft(const BigUnsigned &a, unsigned int b) {
+void BigUnsigned::bitShiftLeft(const BigUnsigned &a, int b) {
        DTRT_ALIASED(this == &a, bitShiftLeft(a, b));
+       if (b < 0) {
+               if (b << 1 == 0)
+                       throw "BigUnsigned::bitShiftLeft: "
+                               "Pathological shift amount not implemented";
+               else {
+                       bitShiftRight(a, -b);
+                       return;
+               }
+       }
        Index shiftBlocks = b / N;
        unsigned int shiftBits = b % N;
        // + 1: room for high bits nudged left into another block
@@ -642,8 +651,17 @@ void BigUnsigned::bitShiftLeft(const BigUnsigned &a, unsigned int b) {
                len--;
 }
 
-void BigUnsigned::bitShiftRight(const BigUnsigned &a, unsigned int b) {
+void BigUnsigned::bitShiftRight(const BigUnsigned &a, int b) {
        DTRT_ALIASED(this == &a, bitShiftRight(a, b));
+       if (b < 0) {
+               if (b << 1 == 0)
+                       throw "BigUnsigned::bitShiftRight: "
+                               "Pathological shift amount not implemented";
+               else {
+                       bitShiftLeft(a, -b);
+                       return;
+               }
+       }
        // This calculation is wacky, but expressing the shift as a left bit shift
        // within each block lets us use getShiftedBlock.
        Index rightShiftBlocks = (b + N - 1) / N;