[fix](decimal256) fix casting decimal256 to float

be/src/vec/data_types/data_type_decimal.h

@@ -645,7 +645,13 @@ void convert_from_decimal(typename ToDataType::FieldType* dst,
         } else {
             auto multiplier = FromDataType::get_scale_multiplier(scale);
             for (size_t i = 0; i < size; ++i) {
-                dst[i] = static_cast<ToFieldType>(src[i].value) / multiplier.value;
+                if constexpr (IsDecimal256<FromFieldType>) {
+                    dst[i] = static_cast<ToFieldType>(static_cast<long double>(src[i].value) /
+                                                      static_cast<long double>(multiplier.value));
+                } else {
+                    dst[i] = static_cast<ToFieldType>(static_cast<double>(src[i].value) /
+                                                      static_cast<double>(multiplier.value));
+                }
             }
         }
         if constexpr (narrow_integral) {

regression-test/data/datatype_p0/decimalv3/test_decimal256_cast.out

@@ -33,6 +33,21 @@
 -- !decimal256_cast10 --
 10	0
 
--- !decimal256_cast_to_double_1 --
+-- !decimal256_cast_to_float1 --
+1.2345678E7
+
+-- !decimal256_cast_to_float2 --
 1.2345678E7
 
+-- !decimal256_cast_to_float3 --
+1	1.2345678E7
+2	1.00000003E16
+3	2.5079478E-7
+4	1.0
+
+-- !decimal256_cast_to_double_1 --
+1	1.2345678E7
+2	1.0E16
+3	2.507947739348449E-7
+4	1.0
+

regression-test/data/datatype_p0/decimalv3/test_decimalv3_cast4.out

@@ -1,6 +1,6 @@
 -- This file is automatically generated. You should know what you did if you want to edit this
 -- !decimal128_to_float_1 --
--9.999999E34
+-1.0E35
 -32769.79
 -32768.79
 -9999.999
@@ -9,9 +9,9 @@
 99.999
 127.789
 9999.999
-32767.787
-32768.125
-9.999999E34
+32767.79
+32768.12
+1.0E35
 
 -- !decimal128_to_double_1 --
 -1.0E35

regression-test/suites/datatype_p0/decimalv3/test_decimal256_cast.groovy

@@ -18,9 +18,9 @@
 suite("test_decimal256_cast") {
     sql "set enable_nereids_planner = true;"
     sql "set enable_decimal256 = true;"
-    // sql """
-    //     set debug_skip_fold_constant=true;
-    // """
+    sql """
+        set debug_skip_fold_constant=true;
+    """
 
     qt_decimal256_cast0 """SELECT /*+ SET_VAR(enable_fold_constant_by_be = false) */
         cast(999999999999999999999999999999999999999999999999999999999999999999.9999999999 as decimalv3(76,10));"""
@@ -74,18 +74,12 @@ suite("test_decimal256_cast") {
         select k1, cast(v1 as decimalv3(76, 0)) from cast_to_dec256 order by k1, v1;
     """
 
-    // test {
-    //     sql """
-    //         select /*+SET_VAR(enable_fold_constant_by_be = true) */cast(cast("12345678.000000000000000000000000000000001" as decimalv3(76, 60)) as float);
-    //     """
-    //     exception "Arithmetic overflow"
-    // }
-    // test {
-    //     sql """
-    //         select /*+SET_VAR(enable_fold_constant_by_be = false) */cast(cast("12345678.000000000000000000000000000000001" as decimalv3(76, 60)) as float);
-    //     """
-    //     exception "Arithmetic overflow"
-    // }
+     qt_decimal256_cast_to_float1 """
+         select /*+SET_VAR(enable_fold_constant_by_be = true) */cast(cast("12345678.000000000000000000000000000000001" as decimalv3(76, 60)) as float);
+     """
+     qt_decimal256_cast_to_float2 """
+         select /*+SET_VAR(enable_fold_constant_by_be = false) */cast(cast("12345678.000000000000000000000000000000001" as decimalv3(76, 60)) as float);
+     """
 
     sql """
         drop table  if exists dec256cast_to_float;
@@ -100,16 +94,64 @@ suite("test_decimal256_cast") {
     );
     """
     sql """
-        insert into dec256cast_to_float values  (1, "12345678.000000000000000000000000000000001");
+        insert into dec256cast_to_float values 
+            (1, "12345678.000000000000000000000000000000001"),
+            (2, "9999999999999999.999999999999999999999999999999999999999999999999999999999999"),
+            (3, "0.000000250794773934844880991039000000000000000000000000000000"),
+            (4, "0.999999999999999999999999999999999999999999999999999999999999");
+    """
+
+    qt_decimal256_cast_to_float3 """
+        select k1, cast(v1 as float) from dec256cast_to_float order by 1;
+    """
+    qt_decimal256_cast_to_double_1 """
+        select k1, cast(v1 as double) from dec256cast_to_float order by 1;
     """
+
     test {
-        sql """
-            select cast(v1 as float) from dec256cast_to_float;
-        """
+        sql """select /*+SET_VAR(debug_skip_fold_constant = false) */cast(cast("1000000000000000000000000000000000000000000000000000000000000000000000.111111" as decimalv3(76, 6)) as float);"""
         exception "Arithmetic overflow"
     }
-    qt_decimal256_cast_to_double_1 """
-        select cast(v1 as double) from dec256cast_to_float;
+    test {
+        sql """select /*+SET_VAR(debug_skip_fold_constant = true) */cast(cast("1000000000000000000000000000000000000000000000000000000000000000000000.111111" as decimalv3(76, 6)) as float);"""
+        exception "Arithmetic overflow"
+    }
+
+    test {
+        sql """select /*+SET_VAR(debug_skip_fold_constant = false) */cast(cast("9999999999999999999999999999999999999999999999999999999999999999999999.999999" as decimalv3(76, 6)) as float);"""
+        exception "Arithmetic overflow"
+    }
+    test {
+        sql """select /*+SET_VAR(debug_skip_fold_constant = true) */cast(cast("9999999999999999999999999999999999999999999999999999999999999999999999.999999" as decimalv3(76, 6)) as float);"""
+        exception "Arithmetic overflow"
+    }
+
+    sql "drop table if exists dec256cast_to_float_overflow"
+    sql """
+    create table dec256cast_to_float_overflow (
+        k1 int,
+        v1 decimalv3(76, 6)
+    ) distributed by hash(k1)
+    properties (
+        'replication_num' = '1'
+    );
+    """
+    sql """
+        insert into dec256cast_to_float_overflow values  (1, "1000000000000000000000000000000000000000000000000000000000000000000000.111111");
+    """
+    test {
+        sql "select cast(v1 as float) from dec256cast_to_float_overflow;"
+        exception "Arithmetic overflow"
+    }
+    sql """
+        truncate table dec256cast_to_float_overflow;
     """
+    sql """
+        insert into dec256cast_to_float_overflow values  (1, "9999999999999999999999999999999999999999999999999999999999999999999999.999999");
+    """
+    test {
+        sql "select cast(v1 as float) from dec256cast_to_float_overflow;"
+        exception "Arithmetic overflow"
+    }
 
 }