Fix an error in BigInt operator-

(x) - (-x) would result in -2x instead of the correct 2x

3 files changed, 59 insertions, 6 deletions

diff --git a/src/lib/math/bigint/big_ops3.cpp b/src/lib/math/bigint/big_ops3.cpp
index eed8a29a0..680eca635 100644
--- a/src/lib/math/bigint/big_ops3.cpp
+++ b/src/lib/math/bigint/big_ops3.cpp
@@ -66,6 +66,7 @@ BigInt operator-(const BigInt& x, const BigInt& y)
       {
       if(x.sign() != y.sign())
          bigint_shl2(z.mutable_data(), x.data(), x_sw, 0, 1);
+      z.set_sign(y.reverse_sign());
       }
    else if(relative_size > 0)
       {
diff --git a/src/tests/data/bn/add.vec b/src/tests/data/bn/add.vec
index d7fb72d57..4829e1706 100644
--- a/src/tests/data/bn/add.vec
+++ b/src/tests/data/bn/add.vec
@@ -15,9 +15,29 @@ In1 = 0x1
 In2 = 0x1
 Output = 0x2
 
-In1 = 0x1
-In2 = -0x1
-Output = 0x0
+In1 = 1
+In2 = -1
+Output = 0
+
+In1 = -1
+In2 = 1
+Output = 0
+
+In1 = -1
+In2 = -1
+Output = -2
+
+In1 = 1
+In2 = -2
+Output = -1
+
+In1 = -2
+In2 = 1
+Output = -1
+
+In1 = -2
+In2 = -1
+Output = -3
 
 In1 = 0x5
 In2 = 0x0
diff --git a/src/tests/data/bn/sub.vec b/src/tests/data/bn/sub.vec
index 5b649ef87..a3cac4206 100644
--- a/src/tests/data/bn/sub.vec
+++ b/src/tests/data/bn/sub.vec
@@ -7,9 +7,41 @@ In1 = 0x0
 In2 = 0x1
 Output = -0x1
 
-In1 = 0x1
-In2 = -0x1
-Output = 0x2
+In1 = 1
+In2 = -1
+Output = 2
+
+In1 = -1
+In2 = 1
+Output = -2
+
+In1 = -1
+In2 = -1
+Output = 0
+
+In1 = 1
+In2 = 1
+Output = 0
+
+In1 = 1
+In2 = -1
+Output = 2
+
+In1 = 1
+In2 = -2
+Output = 3
+
+In1 = -1
+In2 = 2
+Output = -3
+
+In1 = -3
+In2 = -1
+Output = -2
+
+In1 = -3
+In2 = 1
+Output = -4
 
 In1 = 0x64
 In2 = -0x64