From 1686b69fb6fc43018397cec69f99023ee6081d08 Mon Sep 17 00:00:00 2001
From: Paul Mason <paul@paulmason.me>
Date: Fri, 10 Nov 2023 09:34:35 -0800
Subject: [PATCH] Fixes issue whereby scale 29 is required however is optimized
 away (#619)

* Fixes issue whereby scale 29 is required however is optimized away
* Disable test for legacy ops
---
 src/ops/add.rs         |  6 ++++--
 tests/decimal_tests.rs | 34 ++++++++++++++++++++++++++++++++++
 2 files changed, 38 insertions(+), 2 deletions(-)

diff --git a/src/ops/add.rs b/src/ops/add.rs
index 52ba675f..9a0c5bd9 100644
--- a/src/ops/add.rs
+++ b/src/ops/add.rs
@@ -1,4 +1,6 @@
-use crate::constants::{MAX_I32_SCALE, POWERS_10, SCALE_MASK, SCALE_SHIFT, SIGN_MASK, U32_MASK, U32_MAX};
+use crate::constants::{
+    MAX_I32_SCALE, MAX_PRECISION_U32, POWERS_10, SCALE_MASK, SCALE_SHIFT, SIGN_MASK, U32_MASK, U32_MAX,
+};
 use crate::decimal::{CalculationResult, Decimal};
 use crate::ops::common::{Buf24, Dec64};
 
@@ -261,7 +263,7 @@ fn unaligned_add(
 
         rescale_factor -= MAX_I32_SCALE;
 
-        if tmp64 > U32_MAX {
+        if tmp64 > U32_MAX || scale > MAX_PRECISION_U32 {
             break;
         } else {
             high = tmp64 as u32;
diff --git a/tests/decimal_tests.rs b/tests/decimal_tests.rs
index fd1d6775..1eca9b17 100644
--- a/tests/decimal_tests.rs
+++ b/tests/decimal_tests.rs
@@ -4746,4 +4746,38 @@ mod issues {
         assert!(c.is_some());
         assert_eq!("-429391.87200000000002327170816", c.unwrap().to_string())
     }
+
+    #[test]
+    #[cfg(not(feature = "legacy-ops"))] // I will deprecate this feature/behavior in an upcoming release
+    fn issue_618_rescaling_overflow() {
+        fn assert_result(scale: u32, v1: Decimal, v2: Decimal) {
+            assert_eq!(scale, v1.scale(), "initial scale: {scale}");
+            let result1 = v1 + -v2;
+            assert_eq!(
+                result1.to_string(),
+                "-0.0999999999999999999999999999",
+                "a + -b : {scale}"
+            );
+            assert_eq!(28, result1.scale(), "a + -b : {scale}");
+            let result2 = v1 - v2;
+            assert_eq!(
+                result2.to_string(),
+                "-0.0999999999999999999999999999",
+                "a - b : {scale}"
+            );
+            assert_eq!(28, result2.scale(), "a - b : {scale}");
+        }
+
+        let mut a = Decimal::from_str("0.0000000000000000000000000001").unwrap();
+        let b = Decimal::from_str("0.1").unwrap();
+        assert_result(28, a, b);
+
+        // Try at a new scale (this works)
+        a.rescale(30);
+        assert_result(30, a, b);
+
+        // And finally the scale causing an issue
+        a.rescale(29);
+        assert_result(29, a, b);
+    }
 }