Add fp_t subtraction

1 files changed, 16 insertions, 0 deletions

diff --git a/tests/test_fixed_point.cpp b/tests/test_fixed_point.cpp
index b3d3e78..b116340 100644
--- a/tests/test_fixed_point.cpp
+++ b/tests/test_fixed_point.cpp
@@ -8,9 +8,25 @@ TEST_CASE("fp_t addition is commutative") {
     REQUIRE(a.raw != 0);
 }
 
+TEST_CASE("fp_t subtraction anti-commutative") {
+    fp_t a = fp_t::from_int(3);
+    fp_t b = fp_t::from_int(2);
+    fp_t c = fp_t::from_int(1);
+    fp_t d = fp_t::from_int(-1);
+    CHECK((a - b == c && b - a == d));
+    REQUIRE(a.raw != 0);
+}
+
 TEST_CASE("fp_t addition overflows") {
     fp_t a = fp_t::from_raw(INT32_MAX);
     fp_t b = fp_t::from_raw(1);
     fp_t c = fp_t::from_raw(INT32_MIN);
     CHECK(a + b == c);
 }
+
+TEST_CASE("fp_t subtraction underflows") {
+    fp_t a = fp_t::from_raw(INT32_MIN);
+    fp_t b = fp_t::from_raw(1);
+    fp_t c = fp_t::from_raw(INT32_MAX);
+    CHECK(a - b == c);
+}