Fixed negation to properly carry to higher bits.

apache · Oct 27, 2023 · a756f45 · a756f45
1 parent a7f46a7
commit a756f45
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Showing 2 changed files with 11 additions and 7 deletions.
diff --git a/csharp/src/Apache.Arrow/DecimalUtility.cs b/csharp/src/Apache.Arrow/DecimalUtility.cs
@@ -81,18 +81,23 @@ internal static SqlDecimal GetSqlDecimal128(in ArrowBuffer valueBuffer, int inde
         {
             const int byteWidth = 16;
             const int intWidth = byteWidth / 4;
+            const int longWidth = byteWidth / 8;
 
             byte mostSignificantByte = valueBuffer.Span[(index + 1) * byteWidth - 1];
             bool isPositive = (mostSignificantByte & 0x80) == 0;
 
-            ReadOnlySpan<int> value = valueBuffer.Span.CastTo<int>().Slice(index * intWidth, intWidth);
             if (isPositive)
             {
+                ReadOnlySpan<int> value = valueBuffer.Span.CastTo<int>().Slice(index * intWidth, intWidth);
                 return new SqlDecimal((byte)precision, (byte)scale, true, value[0], value[1], value[2], value[3]);
             }
             else
             {
-                return new SqlDecimal((byte)precision, (byte)scale, false, -value[0], ~value[1], ~value[2], ~value[3]);
+                ReadOnlySpan<long> value = valueBuffer.Span.CastTo<long>().Slice(index * longWidth, longWidth);
+                long data1 = -value[0];
+                long data2 = (data1 == 0) ? -value[1] : ~value[1];
+
+                return new SqlDecimal((byte)precision, (byte)scale, false, (int)(data1 & 0xffffffff), (int)(data1 >> 32), (int)(data2 & 0xffffffff), (int)(data2 >> 32));
             }
         }
 #endif
@@ -207,10 +212,9 @@ internal static void GetBytes(SqlDecimal value, int precision, int scale, Span<b
             value.Data.AsSpan().CopyTo(span);
             if (!value.IsPositive)
             {
-                span[0] = -span[0];
-                span[1] = ~span[1];
-                span[2] = ~span[2];
-                span[3] = ~span[3];
+                Span<long> longSpan = bytes.CastTo<long>();
+                longSpan[0] = -longSpan[0];
+                longSpan[1] = (longSpan[0] == 0) ? -longSpan[1] : ~longSpan[1];
             }
         }
 #endif

diff --git a/csharp/test/Apache.Arrow.Tests/DecimalUtilityTests.cs b/csharp/test/Apache.Arrow.Tests/DecimalUtilityTests.cs
@@ -81,7 +81,7 @@ public void NegativeSqlDecimal()
                 const int scale = 0;
                 const int bitWidth = 16;
 
-                var negative = new SqlDecimal(precision, scale, false, -1, -1, 1, 0);
+                var negative = new SqlDecimal(precision, scale, false, 0, 0, 1, 0);
                 var bytes = new byte[16];
                 DecimalUtility.GetBytes(negative.Value, precision, scale, bitWidth, bytes);
                 var sqlNegative = DecimalUtility.GetSqlDecimal128(new ArrowBuffer(bytes), 0, precision, scale);