From 9d4f68606c919791d44e86e7a50812c29be32fa3 Mon Sep 17 00:00:00 2001
From: batsumaru <>
Date: Sun, 9 Aug 2026 12:00:27 +0900
Subject: Add fp_t subtraction

---
 tests/test_fixed_point.cpp | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

(limited to 'tests')

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);
+}
-- 
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