From b100859a1e2ff1b89193c2cdbb484c199c56b591 Mon Sep 17 00:00:00 2001
From: "Shane F. Carr" <sffc@google.com>
Date: Tue, 6 Oct 2020 09:00:53 -0500
Subject: [PATCH] Limit magnitudes of From<FixedDecimal> for PluralOperands to
 prevent overflow. (#293)

---
 components/pluralrules/src/operands.rs        |  7 +++--
 .../pluralrules/tests/fixtures/operands.json  | 28 +++++++++++++++++++
 2 files changed, 32 insertions(+), 3 deletions(-)

diff --git a/components/pluralrules/src/operands.rs b/components/pluralrules/src/operands.rs
index ea28c914729..389e2770be0 100644
--- a/components/pluralrules/src/operands.rs
+++ b/components/pluralrules/src/operands.rs
@@ -201,11 +201,12 @@ impl_integer_type!(u8 u16 u32 u64 u128 usize);
 impl_signed_integer_type!(i8 i16 i32 i64 i128 isize);
 
 impl From<&FixedDecimal> for PluralOperands {
-    /// Converts a [icu_num_util::FixedDecimal] to [PluralOperands]
+    /// Converts a [icu_num_util::FixedDecimal] to [PluralOperands]. Retains at most 18
+    /// digits each from the integer and fraction parts.
     fn from(dec: &FixedDecimal) -> Self {
         let mag_range = dec.magnitude_range();
-        let mag_high = *mag_range.end();
-        let mag_low = *mag_range.start();
+        let mag_high = std::cmp::min(17, *mag_range.end());
+        let mag_low = std::cmp::max(-18, *mag_range.start());
 
         let mut i: u64 = 0;
         for magnitude in (0..=mag_high).rev() {
diff --git a/components/pluralrules/tests/fixtures/operands.json b/components/pluralrules/tests/fixtures/operands.json
index a2c5feb31cd..a40cbf8fa81 100644
--- a/components/pluralrules/tests/fixtures/operands.json
+++ b/components/pluralrules/tests/fixtures/operands.json
@@ -215,6 +215,34 @@
         "f": 0,
         "t": 0
       }
+    },
+    {
+      "input": {
+        "from": 9876543010,
+        "pow10": 10
+      },
+      "expected": {
+        "n": 765430100000000000,
+        "i": 765430100000000000,
+        "v": 0,
+        "w": 0,
+        "f": 0,
+        "t": 0
+      }
+    },
+    {
+      "input": {
+        "from": 9876543010,
+        "pow10": -20
+      },
+      "expected": {
+        "n": 0.000000000098765430,
+        "i": 0,
+        "v": 18,
+        "w": 17,
+        "f": 98765430,
+        "t": 9876543
+      }
     }
   ]
 }