From 3b9f99af67d1d9bb89fc80a4fc93130451c56805 Mon Sep 17 00:00:00 2001
From: Benedikt Reinartz <filmor@gmail.com>
Date: Tue, 12 Mar 2024 22:53:29 +0100
Subject: [PATCH] Fix 128 bit decoding and add more tests

---
 rustler/src/types/i128.rs              | 16 +++++++++-------
 rustler_tests/test/primitives_test.exs | 18 ++++++++++++++++--
 2 files changed, 25 insertions(+), 9 deletions(-)

diff --git a/rustler/src/types/i128.rs b/rustler/src/types/i128.rs
index ae76e41b..b79a4d0c 100644
--- a/rustler/src/types/i128.rs
+++ b/rustler/src/types/i128.rs
@@ -71,16 +71,18 @@ impl<'a> Decoder<'a> for i128 {
             return Err(Error::BadArg);
         }
 
-        let mut res = [0u8; 16];
-        res[16 - n..].copy_from_slice(&input[4..4 + n]);
-        let res = i128::from_le_bytes(res);
-        if res < 0 {
-            // The stored data is supposed to be unsigned, so if we interpret it as negative here,
-            // it was too large.
+        let is_pos = input[3] == 0;
+
+        let mut res = [0; 16];
+        res[..n].copy_from_slice(&input[4..4 + n]);
+
+        if res[15] >= 128 && is_pos {
+            // Value is too large for i128
             return Err(Error::BadArg);
         }
 
-        if input[3] == 0 {
+        let res = i128::from_le_bytes(res);
+        if is_pos {
             Ok(res)
         } else {
             Ok(-res)
diff --git a/rustler_tests/test/primitives_test.exs b/rustler_tests/test/primitives_test.exs
index 10b8d6fd..d1a8f4f8 100644
--- a/rustler_tests/test/primitives_test.exs
+++ b/rustler_tests/test/primitives_test.exs
@@ -40,14 +40,25 @@ defmodule RustlerTest.PrimitivesTest do
     assert i == RustlerTest.echo_i128(i)
     assert -i == RustlerTest.echo_i128(-i)
 
+    i = 1 <<< 80
+    assert i == RustlerTest.echo_i128(i)
+    assert -i == RustlerTest.echo_i128(-i)
+
     i = 1 <<< 126
     assert i == RustlerTest.echo_i128(i)
     assert -i == RustlerTest.echo_i128(-i)
 
+    i = -170141183460469231731687303715884105728 # i128::min_value()
+    assert i == RustlerTest.echo_i128(i)
+
+    i = 170141183460469231731687303715884105727 # i128::max_value()
+    assert i == RustlerTest.echo_i128(i)
+
+    i = 0xFFFF_FFFF_FFFF_FFFF_FFFF_FFFF_FFFF_FFFF # u128::max_value()
     assert_raise ArgumentError, fn -> RustlerTest.echo_i128(:non_int) end
     assert_raise ArgumentError, fn -> RustlerTest.echo_i128(123.45) end
-    assert_raise ArgumentError, fn -> RustlerTest.echo_i128(1 <<< 127) end
     assert_raise ArgumentError, fn -> RustlerTest.echo_i128(1 <<< 128) end
+    assert_raise ArgumentError, fn -> RustlerTest.echo_i128(i) end
   end
 
   test "u128 support" do
@@ -59,8 +70,11 @@ defmodule RustlerTest.PrimitivesTest do
     i = 1 <<< 127
     assert i == RustlerTest.echo_u128(i)
 
+    i = 0xFFFF_FFFF_FFFF_FFFF_FFFF_FFFF_FFFF_FFFF # u128::max_value()
+    assert i == RustlerTest.echo_u128(i)
+
     assert_raise ArgumentError, fn -> RustlerTest.echo_u128(:non_int) end
     assert_raise ArgumentError, fn -> RustlerTest.echo_u128(123.45) end
-    assert_raise ArgumentError, fn -> RustlerTest.echo_i128(1 <<< 128) end
+    assert_raise ArgumentError, fn -> RustlerTest.echo_i128(1 <<< 129) end
   end
 end