Fix bigint shift-right partial shift

ziglang · May 10, 2018 · efa39c5 · efa39c5
1 parent c3ddf50
commit efa39c5
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Showing 2 changed files with 9 additions and 1 deletion.
diff --git a/src/bigint.cpp b/src/bigint.cpp
@@ -1425,7 +1425,7 @@ void bigint_shr(BigInt *dest, const BigInt *op1, const BigInt *op2) {
         uint64_t digit = op1_digits[op_digit_index];
         size_t dest_digit_index = op_digit_index - digit_shift_count;
         dest->data.digits[dest_digit_index] = carry | (digit >> leftover_shift_count);
-        carry = digit << leftover_shift_count;
+        carry = digit << (64 - leftover_shift_count);
 
         if (dest_digit_index == 0) { break; }
         op_digit_index -= 1;

diff --git a/test/cases/math.zig b/test/cases/math.zig
@@ -366,6 +366,14 @@ test "big number multi-limb shift and mask" {
     }
 }
 
+test "big number multi-limb partial shift right" {
+    comptime {
+        var a = 0x1ffffffffeeeeeeee;
+        a >>= 16;
+        assert(a == 0x1ffffffffeeee);
+    }
+}
+
 test "xor" {
     test_xor();
     comptime test_xor();