SERVER-72621 truncate v_prime2

2 files changed, 11 insertions, 0 deletions

diff --git a/src/mongo/crypto/fle_crypto.cpp b/src/mongo/crypto/fle_crypto.cpp
index c5bda150f5f..70c37d22ce7 100644
--- a/src/mongo/crypto/fle_crypto.cpp
+++ b/src/mongo/crypto/fle_crypto.cpp
@@ -4004,6 +4004,11 @@ OSTType_Decimal128 getTypeInfoDecimal128(Decimal128 value,
         //
         // Returns 3141.0
         Decimal128 v_prime2 = v_prime.subtract(min.get()).scale(precision.get());
+        // Round the number down again. min may have a fractional value with more decimal places
+        // than the precision (e.g. .001). Subtracting min may have resulted in v_prime2 with
+        // a non-zero fraction. v_prime2 is expected to have no fractional value when
+        // converting to int128.
+        v_prime2 = v_prime2.round(Decimal128::kRoundTowardZero);
 
         invariant(v_prime2.logarithm(Decimal128(2)).isLess(Decimal128(128)));
 
diff --git a/src/mongo/crypto/fle_crypto_test.cpp b/src/mongo/crypto/fle_crypto_test.cpp
index 538211edd9f..e655d10cd2b 100644
--- a/src/mongo/crypto/fle_crypto_test.cpp
+++ b/src/mongo/crypto/fle_crypto_test.cpp
@@ -2768,6 +2768,12 @@ TEST(RangeTest, Decimal128_Bounds_Precision) {
 
     ASSERT_EIBB(5E-30, 10E-30, 1E-30, 35, boost::multiprecision::uint128_t("400000"));
 
+    // Test a range that requires > 64 bits.
+    ASSERT_EIBB(5, "18446744073709551616", ".1", 1, 49)
+    // Test a range that requires > 64 bits.
+    // min has more places after the decimal than precision.
+    ASSERT_EIBB(5, "18446744073709551616", ".01", 1, 49)
+
 #undef ASSERT_EIBB
 #undef ASSERT_EIBB_OVERFLOW
 }