diff --git a/gcc/builtin-types.def b/gcc/builtin-types.def
index 25da582ce58..66ce164828f 100644
--- a/gcc/builtin-types.def
+++ b/gcc/builtin-types.def
@@ -202,6 +202,9 @@ DEF_PRIMITIVE_TYPE (BT_DFLOAT64, (dfloat64_type_node
 DEF_PRIMITIVE_TYPE (BT_DFLOAT128, (dfloat128_type_node
 				   ? dfloat128_type_node
 				   : error_mark_node))
+DEF_PRIMITIVE_TYPE (BT_DFLOAT64X, (dfloat64x_type_node
+				   ? dfloat64x_type_node
+				   : error_mark_node))
 
 DEF_PRIMITIVE_TYPE (BT_VALIST_REF, va_list_ref_type_node)
 DEF_PRIMITIVE_TYPE (BT_VALIST_ARG, va_list_arg_type_node)
@@ -249,6 +252,7 @@ DEF_FUNCTION_TYPE_0 (BT_FN_FLOAT128X, BT_FLOAT128X)
 DEF_FUNCTION_TYPE_0 (BT_FN_DFLOAT32, BT_DFLOAT32)
 DEF_FUNCTION_TYPE_0 (BT_FN_DFLOAT64, BT_DFLOAT64)
 DEF_FUNCTION_TYPE_0 (BT_FN_DFLOAT128, BT_DFLOAT128)
+DEF_FUNCTION_TYPE_0 (BT_FN_DFLOAT64X, BT_DFLOAT64X)
 
 DEF_FUNCTION_TYPE_1 (BT_FN_LONG_LONG, BT_LONG, BT_LONG)
 DEF_FUNCTION_TYPE_1 (BT_FN_LONGLONG_LONGLONG, BT_LONGLONG, BT_LONGLONG)
@@ -377,6 +381,8 @@ DEF_FUNCTION_TYPE_1 (BT_FN_DFLOAT32_CONST_STRING, BT_DFLOAT32, BT_CONST_STRING)
 DEF_FUNCTION_TYPE_1 (BT_FN_DFLOAT64_CONST_STRING, BT_DFLOAT64, BT_CONST_STRING)
 DEF_FUNCTION_TYPE_1 (BT_FN_DFLOAT128_CONST_STRING,
 		     BT_DFLOAT128, BT_CONST_STRING)
+DEF_FUNCTION_TYPE_1 (BT_FN_DFLOAT64X_CONST_STRING, BT_DFLOAT64X,
+		     BT_CONST_STRING)
 DEF_FUNCTION_TYPE_1 (BT_FN_STRING_CONST_STRING, BT_STRING, BT_CONST_STRING)
 DEF_FUNCTION_TYPE_1 (BT_FN_UNWINDWORD_PTR, BT_UNWINDWORD, BT_PTR)
 DEF_FUNCTION_TYPE_1 (BT_FN_INT_WINT, BT_INT, BT_WINT)
@@ -384,6 +390,7 @@ DEF_FUNCTION_TYPE_1 (BT_FN_WINT_WINT, BT_WINT, BT_WINT)
 DEF_FUNCTION_TYPE_1 (BT_FN_DFLOAT32_DFLOAT32, BT_DFLOAT32, BT_DFLOAT32)
 DEF_FUNCTION_TYPE_1 (BT_FN_DFLOAT64_DFLOAT64, BT_DFLOAT64, BT_DFLOAT64)
 DEF_FUNCTION_TYPE_1 (BT_FN_DFLOAT128_DFLOAT128, BT_DFLOAT128, BT_DFLOAT128)
+DEF_FUNCTION_TYPE_1 (BT_FN_DFLOAT64X_DFLOAT64X, BT_DFLOAT64X, BT_DFLOAT64X)
 DEF_FUNCTION_TYPE_1 (BT_FN_VOID_VPTR, BT_VOID, BT_VOLATILE_PTR)
 DEF_FUNCTION_TYPE_1 (BT_FN_VOID_PTRPTR, BT_VOID, BT_PTR_PTR)
 DEF_FUNCTION_TYPE_1 (BT_FN_VOID_CONST_PTR, BT_VOID, BT_CONST_PTR)
diff --git a/gcc/builtins.cc b/gcc/builtins.cc
index 0d90c2ad5f8..7243c408cf2 100644
--- a/gcc/builtins.cc
+++ b/gcc/builtins.cc
@@ -7851,6 +7851,7 @@ expand_builtin (tree exp, rtx target, rtx subtarget, machine_mode mode,
     case BUILT_IN_FABSD32:
     case BUILT_IN_FABSD64:
     case BUILT_IN_FABSD128:
+    case BUILT_IN_FABSD64X:
       target = expand_builtin_fabs (exp, target, subtarget);
       if (target)
 	return target;
@@ -10447,6 +10448,7 @@ fold_builtin_0 (location_t loc, tree fndecl)
     case BUILT_IN_INFD32:
     case BUILT_IN_INFD64:
     case BUILT_IN_INFD128:
+    case BUILT_IN_INFD64X:
       return fold_builtin_inf (loc, type, true);
 
     CASE_FLT_FN (BUILT_IN_HUGE_VAL):
@@ -10509,6 +10511,7 @@ fold_builtin_1 (location_t loc, tree expr, tree fndecl, tree arg0)
     case BUILT_IN_FABSD32:
     case BUILT_IN_FABSD64:
     case BUILT_IN_FABSD128:
+    case BUILT_IN_FABSD64X:
       return fold_builtin_fabs (loc, arg0, type);
 
     case BUILT_IN_ABS:
diff --git a/gcc/builtins.def b/gcc/builtins.def
index 0c76ebc5e31..4c2f9be43ba 100644
--- a/gcc/builtins.def
+++ b/gcc/builtins.def
@@ -387,6 +387,7 @@ DEF_EXT_LIB_FLOATN_NX_BUILTINS (BUILT_IN_FABS, "fabs", FABS_TYPE, ATTR_CONST_NOT
 DEF_C23_BUILTIN        (BUILT_IN_FABSD32, "fabsd32", BT_FN_DFLOAT32_DFLOAT32, ATTR_CONST_NOTHROW_LEAF_LIST)
 DEF_C23_BUILTIN        (BUILT_IN_FABSD64, "fabsd64", BT_FN_DFLOAT64_DFLOAT64, ATTR_CONST_NOTHROW_LEAF_LIST)
 DEF_C23_BUILTIN        (BUILT_IN_FABSD128, "fabsd128", BT_FN_DFLOAT128_DFLOAT128, ATTR_CONST_NOTHROW_LEAF_LIST)
+DEF_C23_BUILTIN        (BUILT_IN_FABSD64X, "fabsd64x", BT_FN_DFLOAT64X_DFLOAT64X, ATTR_CONST_NOTHROW_LEAF_LIST)
 DEF_C99_BUILTIN        (BUILT_IN_FDIM, "fdim", BT_FN_DOUBLE_DOUBLE_DOUBLE, ATTR_MATHFN_FPROUNDING_ERRNO)
 DEF_C99_BUILTIN        (BUILT_IN_FDIMF, "fdimf", BT_FN_FLOAT_FLOAT_FLOAT, ATTR_MATHFN_FPROUNDING_ERRNO)
 DEF_C99_BUILTIN        (BUILT_IN_FDIML, "fdiml", BT_FN_LONGDOUBLE_LONGDOUBLE_LONGDOUBLE, ATTR_MATHFN_FPROUNDING_ERRNO)
@@ -477,6 +478,7 @@ DEF_GCC_FLOATN_NX_BUILTINS (BUILT_IN_INF, "inf", INF_TYPE, ATTR_CONST_NOTHROW_LE
 DEF_GCC_BUILTIN	       (BUILT_IN_INFD32, "infd32", BT_FN_DFLOAT32, ATTR_CONST_NOTHROW_LEAF_LIST)
 DEF_GCC_BUILTIN        (BUILT_IN_INFD64, "infd64", BT_FN_DFLOAT64, ATTR_CONST_NOTHROW_LEAF_LIST)
 DEF_GCC_BUILTIN        (BUILT_IN_INFD128, "infd128", BT_FN_DFLOAT128, ATTR_CONST_NOTHROW_LEAF_LIST)
+DEF_GCC_BUILTIN        (BUILT_IN_INFD64X, "infd64x", BT_FN_DFLOAT64X, ATTR_CONST_NOTHROW_LEAF_LIST)
 DEF_GCC_BUILTIN        (BUILT_IN_IRINT, "irint", BT_FN_INT_DOUBLE, ATTR_MATHFN_FPROUNDING_ERRNO)
 DEF_GCC_BUILTIN        (BUILT_IN_IRINTF, "irintf", BT_FN_INT_FLOAT, ATTR_MATHFN_FPROUNDING_ERRNO)
 DEF_GCC_BUILTIN        (BUILT_IN_IRINTL, "irintl", BT_FN_INT_LONGDOUBLE, ATTR_MATHFN_FPROUNDING_ERRNO)
@@ -575,6 +577,7 @@ DEF_EXT_LIB_FLOATN_NX_BUILTINS (BUILT_IN_NAN, "nan", NAN_TYPE, ATTR_CONST_NOTHRO
 DEF_C23_BUILTIN        (BUILT_IN_NAND32, "nand32", BT_FN_DFLOAT32_CONST_STRING, ATTR_CONST_NOTHROW_NONNULL)
 DEF_C23_BUILTIN        (BUILT_IN_NAND64, "nand64", BT_FN_DFLOAT64_CONST_STRING, ATTR_CONST_NOTHROW_NONNULL)
 DEF_C23_BUILTIN        (BUILT_IN_NAND128, "nand128", BT_FN_DFLOAT128_CONST_STRING, ATTR_CONST_NOTHROW_NONNULL)
+DEF_C23_BUILTIN        (BUILT_IN_NAND64X, "nand64x", BT_FN_DFLOAT64X_CONST_STRING, ATTR_CONST_NOTHROW_NONNULL)
 DEF_GCC_BUILTIN        (BUILT_IN_NANS, "nans", BT_FN_DOUBLE_CONST_STRING, ATTR_CONST_NOTHROW_NONNULL)
 DEF_GCC_BUILTIN        (BUILT_IN_NANSF, "nansf", BT_FN_FLOAT_CONST_STRING, ATTR_CONST_NOTHROW_NONNULL)
 DEF_GCC_BUILTIN        (BUILT_IN_NANSL, "nansl", BT_FN_LONGDOUBLE_CONST_STRING, ATTR_CONST_NOTHROW_NONNULL)
@@ -584,6 +587,7 @@ DEF_GCC_BUILTIN        (BUILT_IN_NANSF16B, "nansf16b", BT_FN_BFLOAT16_CONST_STRI
 DEF_GCC_BUILTIN        (BUILT_IN_NANSD32, "nansd32", BT_FN_DFLOAT32_CONST_STRING, ATTR_CONST_NOTHROW_NONNULL)
 DEF_GCC_BUILTIN        (BUILT_IN_NANSD64, "nansd64", BT_FN_DFLOAT64_CONST_STRING, ATTR_CONST_NOTHROW_NONNULL)
 DEF_GCC_BUILTIN        (BUILT_IN_NANSD128, "nansd128", BT_FN_DFLOAT128_CONST_STRING, ATTR_CONST_NOTHROW_NONNULL)
+DEF_GCC_BUILTIN        (BUILT_IN_NANSD64X, "nansd64x", BT_FN_DFLOAT64X_CONST_STRING, ATTR_CONST_NOTHROW_NONNULL)
 DEF_C99_BUILTIN        (BUILT_IN_NEARBYINT, "nearbyint", BT_FN_DOUBLE_DOUBLE, ATTR_CONST_NOTHROW_LEAF_LIST)
 DEF_C99_BUILTIN        (BUILT_IN_NEARBYINTF, "nearbyintf", BT_FN_FLOAT_FLOAT, ATTR_CONST_NOTHROW_LEAF_LIST)
 DEF_C99_BUILTIN        (BUILT_IN_NEARBYINTL, "nearbyintl", BT_FN_LONGDOUBLE_LONGDOUBLE, ATTR_CONST_NOTHROW_LEAF_LIST)
diff --git a/gcc/c-family/c-common.cc b/gcc/c-family/c-common.cc
index dae5f5e1c27..b7586312537 100644
--- a/gcc/c-family/c-common.cc
+++ b/gcc/c-family/c-common.cc
@@ -100,7 +100,8 @@ machine_mode c_default_pointer_mode = VOIDmode;
 
 	tree dfloat32_type_node;
 	tree dfloat64_type_node;
-	tree_dfloat128_type_node;
+	tree dfloat128_type_node;
+	tree dfloat64x_type_node; 
 
 	tree intQI_type_node;
 	tree intHI_type_node;
@@ -407,6 +408,7 @@ const struct c_common_resword c_common_reswords[] =
   { "_Decimal32",       RID_DFLOAT32,  D_CONLY },
   { "_Decimal64",       RID_DFLOAT64,  D_CONLY },
   { "_Decimal128",      RID_DFLOAT128, D_CONLY },
+  { "_Decimal64x",      RID_DFLOAT64X, D_CONLY },
   { "_Fract",           RID_FRACT,     D_CONLY | D_EXT },
   { "_Accum",           RID_ACCUM,     D_CONLY | D_EXT },
   { "_Sat",             RID_SAT,       D_CONLY | D_EXT },
@@ -4480,6 +4482,7 @@ c_common_nodes_and_builtins (void)
       record_builtin_type (RID_DFLOAT32, NULL, dfloat32_type_node);
       record_builtin_type (RID_DFLOAT64, NULL, dfloat64_type_node);
       record_builtin_type (RID_DFLOAT128, NULL, dfloat128_type_node);
+      record_builtin_type (RID_DFLOAT64X, NULL, dfloat64x_type_node);
     }
 
   if (targetm.fixed_point_supported_p ())
diff --git a/gcc/c-family/c-common.h b/gcc/c-family/c-common.h
index 3c3da66272b..a74530bafff 100644
--- a/gcc/c-family/c-common.h
+++ b/gcc/c-family/c-common.h
@@ -111,7 +111,7 @@ enum rid
   RID_BUILTIN_SHUFFLEVECTOR,   RID_BUILTIN_CONVERTVECTOR,  RID_BUILTIN_TGMATH,
   RID_BUILTIN_HAS_ATTRIBUTE,   RID_BUILTIN_ASSOC_BARRIER,  RID_BUILTIN_STDC,
   RID_BUILTIN_COUNTED_BY_REF,
-  RID_DFLOAT32, RID_DFLOAT64, RID_DFLOAT128,
+  RID_DFLOAT32, RID_DFLOAT64, RID_DFLOAT128, RID_DFLOAT64X,
 
   /* TS 18661-3 keywords, in the same sequence as the TI_* values.  */
   RID_FLOAT16,
diff --git a/gcc/c-family/c-cppbuiltin.cc b/gcc/c-family/c-cppbuiltin.cc
index 294315aef86..349918c325c 100644
--- a/gcc/c-family/c-cppbuiltin.cc
+++ b/gcc/c-family/c-cppbuiltin.cc
@@ -1323,6 +1323,9 @@ c_cpp_builtins (cpp_reader *pfile)
 					      dfloat64_type_node);
       builtin_define_decimal_float_constants ("DEC128", "DL",
 					      dfloat128_type_node);
+      if (dfloat64x_type_node)
+	builtin_define_decimal_float_constants ("DEC64X", "D64x",
+						dfloat64x_type_node);
     }
 
   /* For fixed-point fibt, ibit, max, min, and epsilon.  */
diff --git a/gcc/c-family/c-lex.cc b/gcc/c-family/c-lex.cc
index 8e182938938..32f19702c79 100644
--- a/gcc/c-family/c-lex.cc
+++ b/gcc/c-family/c-lex.cc
@@ -1235,6 +1235,8 @@ interpret_float (const cpp_token *token, unsigned int flags,
       type = dfloat128_type_node;
     else if ((flags & CPP_N_WIDTH) == CPP_N_SMALL)
       type = dfloat32_type_node;
+    else if ((flags & CPP_N_FLOATNX) != 0)
+      type = dfloat64x_type_node;
     else
       type = dfloat64_type_node;
   else
@@ -1350,6 +1352,8 @@ interpret_float (const cpp_token *token, unsigned int flags,
     {
       if (ISDIGIT (token->val.str.text[copylen - 1]))
 	copylen -= (flags & CPP_N_LARGE) ? 4 : 3;
+      else if ((flags & CPP_N_FLOATNX) != 0)
+	copylen -= 4;
       else
 	copylen -= 2;
     }
diff --git a/gcc/c-family/c-pretty-print.cc b/gcc/c-family/c-pretty-print.cc
index 810e4878049..320f350e600 100644
--- a/gcc/c-family/c-pretty-print.cc
+++ b/gcc/c-family/c-pretty-print.cc
@@ -1159,6 +1159,8 @@ pp_c_floating_constant (c_pretty_printer *pp, tree r)
     pp_string (pp, "dd");
   else if (TREE_TYPE (r) == dfloat32_type_node)
     pp_string (pp, "df");
+  else if (TREE_TYPE (r) == dfloat64x_type_node)
+    pp_string (pp, "d64x");
   else if (TREE_TYPE (r) != double_type_node)
     for (int i = 0; i < NUM_FLOATN_NX_TYPES; i++)
       if (TREE_TYPE (r) == FLOATN_NX_TYPE_NODE (i))
diff --git a/gcc/c/c-decl.cc b/gcc/c/c-decl.cc
index e5045c63673..3a45c02a1eb 100644
--- a/gcc/c/c-decl.cc
+++ b/gcc/c/c-decl.cc
@@ -12119,6 +12119,10 @@ declspecs_add_type (location_t loc, struct c_declspecs *specs,
 		error_at (loc,
 			  ("both %<long%> and %<_Decimal128%> in "
 			   "declaration specifiers"));
+	      else if (specs->typespec_word == cts_dfloat64x)
+		error_at (loc,
+			  ("both %<long%> and %<_Decimal64x%> in "
+			   "declaration specifiers"));
 	      else
 		{
 		  specs->long_p = true;
@@ -12184,6 +12188,10 @@ declspecs_add_type (location_t loc, struct c_declspecs *specs,
 		error_at (loc,
 			  ("both %<short%> and %<_Decimal128%> in "
 			   "declaration specifiers"));
+	      else if (specs->typespec_word == cts_dfloat64x)
+		error_at (loc,
+			  ("both %<short%> and %<_Decimal64x%> in "
+			   "declaration specifiers"));
 	      else
 		{
 		  specs->short_p = true;
@@ -12236,6 +12244,10 @@ declspecs_add_type (location_t loc, struct c_declspecs *specs,
 		error_at (loc,
 			  ("both %<signed%> and %<_Decimal128%> in "
 			   "declaration specifiers"));
+	      else if (specs->typespec_word == cts_dfloat64x)
+		error_at (loc,
+			  ("both %<signed%> and %<_Decimal64x%> in "
+			   "declaration specifiers"));
 	      else
 		{
 		  specs->signed_p = true;
@@ -12288,6 +12300,10 @@ declspecs_add_type (location_t loc, struct c_declspecs *specs,
 		error_at (loc,
 			  ("both %<unsigned%> and %<_Decimal128%> in "
 			   "declaration specifiers"));
+	      else if (specs->typespec_word == cts_dfloat64x)
+		error_at (loc,
+			  ("both %<unsigned%> and %<_Decimal64x%> in "
+			   "declaration specifiers"));
 	      else
 		{
 		  specs->unsigned_p = true;
@@ -12327,6 +12343,10 @@ declspecs_add_type (location_t loc, struct c_declspecs *specs,
 		error_at (loc,
 			  ("both %<complex%> and %<_Decimal128%> in "
 			   "declaration specifiers"));
+	      else if (specs->typespec_word == cts_dfloat64x)
+		error_at (loc,
+			  ("both %<complex%> and %<_Decimal64x%> in "
+			   "declaration specifiers"));
 	      else if (specs->typespec_word == cts_fract)
 		error_at (loc,
 			  ("both %<complex%> and %<_Fract%> in "
@@ -12408,6 +12428,10 @@ declspecs_add_type (location_t loc, struct c_declspecs *specs,
 		error_at (loc,
 			  ("both %<_Sat%> and %<_Decimal128%> in "
 			   "declaration specifiers"));
+	      else if (specs->typespec_word == cts_dfloat64x)
+		error_at (loc,
+			  ("both %<_Sat%> and %<_Decimal64x%> in "
+			   "declaration specifiers"));
 	      else if (specs->complex_p)
 		error_at (loc,
 			  ("both %<_Sat%> and %<complex%> in "
@@ -12733,14 +12757,17 @@ declspecs_add_type (location_t loc, struct c_declspecs *specs,
 	    case RID_DFLOAT32:
 	    case RID_DFLOAT64:
 	    case RID_DFLOAT128:
+	    case RID_DFLOAT64X:
 	      {
 		const char *str;
 		if (i == RID_DFLOAT32)
 		  str = "_Decimal32";
 		else if (i == RID_DFLOAT64)
 		  str = "_Decimal64";
-		else
+		else if (i == RID_DFLOAT128)
 		  str = "_Decimal128";
+		else
+		  str = "_Decimal64x";
 		if (specs->long_long_p)
 		  error_at (loc,
 			    ("both %<long long%> and %qs in "
@@ -12780,8 +12807,10 @@ declspecs_add_type (location_t loc, struct c_declspecs *specs,
 		  specs->typespec_word = cts_dfloat32;
 		else if (i == RID_DFLOAT64)
 		  specs->typespec_word = cts_dfloat64;
-		else
+		else if (i == RID_DFLOAT128)
 		  specs->typespec_word = cts_dfloat128;
+		else
+		  specs->typespec_word = cts_dfloat64x;
 		specs->locations[cdw_typespec] = loc;
 	      }
 	      if (!targetm.decimal_float_supported_p ())
@@ -13350,6 +13379,7 @@ finish_declspecs (struct c_declspecs *specs)
     case cts_dfloat32:
     case cts_dfloat64:
     case cts_dfloat128:
+    case cts_dfloat64x:
       gcc_assert (!specs->long_p && !specs->long_long_p && !specs->short_p
 		  && !specs->signed_p && !specs->unsigned_p && !specs->complex_p);
       if (!targetm.decimal_float_supported_p ())
@@ -13358,8 +13388,10 @@ finish_declspecs (struct c_declspecs *specs)
 	specs->type = dfloat32_type_node;
       else if (specs->typespec_word == cts_dfloat64)
 	specs->type = dfloat64_type_node;
-      else
+      else if (specs->typespec_word == cts_dfloat128)
 	specs->type = dfloat128_type_node;
+      else
+	specs->type = dfloat64x_type_node;
       break;
     case cts_fract:
       gcc_assert (!specs->complex_p);
diff --git a/gcc/c/c-parser.cc b/gcc/c/c-parser.cc
index 3ab8a49bf35..70fbf940835 100644
--- a/gcc/c/c-parser.cc
+++ b/gcc/c/c-parser.cc
@@ -597,6 +597,7 @@ c_keyword_starts_typename (enum rid keyword)
     case RID_DFLOAT32:
     case RID_DFLOAT64:
     case RID_DFLOAT128:
+    case RID_DFLOAT64X:
     CASE_RID_FLOATN_NX:
     case RID_BOOL:
     case RID_BITINT:
@@ -801,6 +802,7 @@ c_token_starts_declspecs (c_token *token)
 	case RID_DFLOAT32:
 	case RID_DFLOAT64:
 	case RID_DFLOAT128:
+	case RID_DFLOAT64X:
 	CASE_RID_FLOATN_NX:
 	case RID_BOOL:
 	case RID_BITINT:
@@ -3505,6 +3507,7 @@ c_parser_declspecs (c_parser *parser, struct c_declspecs *specs,
 	case RID_DFLOAT32:
 	case RID_DFLOAT64:
 	case RID_DFLOAT128:
+	case RID_DFLOAT64X:
 	CASE_RID_FLOATN_NX:
 	case RID_BOOL:
 	case RID_FRACT:
@@ -5229,6 +5232,7 @@ c_parser_gnu_attribute_any_word (c_parser *parser)
 	case RID_DFLOAT32:
 	case RID_DFLOAT64:
 	case RID_DFLOAT128:
+	case RID_DFLOAT64X:
 	CASE_RID_FLOATN_NX:
 	case RID_BOOL:
 	case RID_BITINT:
@@ -11897,6 +11901,7 @@ c_parser_postfix_expression (c_parser *parser)
 	    bool arg_binary = all_binary;
 	    bool arg_int_decimal = all_decimal;
 	    bool arg_int_floatnx = false;
+	    bool arg_int_decimalx = false;
 	    for (unsigned int j = 1; j <= nargs; j++)
 	      {
 		if (parm_kind[j] == tgmath_fixed)
@@ -12001,6 +12006,8 @@ c_parser_postfix_expression (c_parser *parser)
 			arg_int_floatnx = true;
 			break;
 		      }
+		if (rtype == dfloat64x_type_node)
+		  arg_int_decimalx = true;
 	      }
 	    tree arg_real = NULL_TREE;
 	    for (unsigned int j = 1; j <= nargs; j++)
@@ -12012,10 +12019,12 @@ c_parser_postfix_expression (c_parser *parser)
 		if (TREE_CODE (type) == COMPLEX_TYPE)
 		  type = TREE_TYPE (type);
 		if (INTEGRAL_TYPE_P (type))
-		  type = (arg_int_decimal
-			  ? dfloat64_type_node
+		  type = (arg_int_decimalx
+			  ? dfloat64x_type_node
 			  : arg_int_floatnx
 			  ? float32x_type_node
+			  : arg_int_decimal
+			  ? dfloat64_type_node
 			  : double_type_node);
 		if (arg_real == NULL_TREE)
 		  arg_real = type;
@@ -13173,6 +13182,7 @@ warn_for_abs (location_t loc, tree fndecl, tree arg)
     case BUILT_IN_FABSD32:
     case BUILT_IN_FABSD64:
     case BUILT_IN_FABSD128:
+    case BUILT_IN_FABSD64X:
       if (!DECIMAL_FLOAT_TYPE_P (atype))
 	{
 	  if (INTEGRAL_TYPE_P (atype))
diff --git a/gcc/c/c-tree.h b/gcc/c/c-tree.h
index f6bcbabb9d5..d39bd238103 100644
--- a/gcc/c/c-tree.h
+++ b/gcc/c/c-tree.h
@@ -287,8 +287,8 @@ enum c_storage_class {
 };
 
 /* A type specifier keyword "void", "_Bool", "char", "int", "float",
-   "double", "_Decimal32", "_Decimal64", "_Decimal128", "_Fract", "_Accum",
-   "_BitInt", or none of these.  */
+   "double", "_Decimal32", "_Decimal64", "_Decimal128", "_Decimal64x",
+   "_Fract", "_Accum", "_BitInt", or none of these.  */
 enum c_typespec_keyword {
   cts_none,
   cts_void,
@@ -301,6 +301,7 @@ enum c_typespec_keyword {
   cts_dfloat32,
   cts_dfloat64,
   cts_dfloat128,
+  cts_dfloat64x,
   cts_floatn_nx,
   cts_fract,
   cts_accum,
diff --git a/gcc/c/c-typeck.cc b/gcc/c/c-typeck.cc
index ced58c2be84..10b02da8752 100644
--- a/gcc/c/c-typeck.cc
+++ b/gcc/c/c-typeck.cc
@@ -1158,6 +1158,11 @@ c_common_type (tree t1, tree t2)
       if (TYPE_MAIN_VARIANT (t1) == dfloat128_type_node
 	  || TYPE_MAIN_VARIANT (t2) == dfloat128_type_node)
 	return dfloat128_type_node;
+      /* And prefer _Decimal128 over _Decimal64x which has in GCC's
+	 implementation the same mode.  */
+      else if (TYPE_MAIN_VARIANT (t1) == dfloat64x_type_node
+	       || TYPE_MAIN_VARIANT (t2) == dfloat64x_type_node)
+	return dfloat64x_type_node;
       else if (TYPE_MAIN_VARIANT (t1) == dfloat64_type_node
 	       || TYPE_MAIN_VARIANT (t2) == dfloat64_type_node)
 	return dfloat64_type_node;
diff --git a/gcc/fold-const-call.cc b/gcc/fold-const-call.cc
index 47bf8d64391..23fa832afa0 100644
--- a/gcc/fold-const-call.cc
+++ b/gcc/fold-const-call.cc
@@ -1350,6 +1350,7 @@ fold_const_call (combined_fn fn, tree type, tree arg)
     case CFN_BUILT_IN_NAND32:
     case CFN_BUILT_IN_NAND64:
     case CFN_BUILT_IN_NAND128:
+    case CFN_BUILT_IN_NAND64X:
       return fold_const_builtin_nan (type, arg, true);
 
     CASE_CFN_NANS:
@@ -1358,6 +1359,7 @@ fold_const_call (combined_fn fn, tree type, tree arg)
     case CFN_BUILT_IN_NANSD32:
     case CFN_BUILT_IN_NANSD64:
     case CFN_BUILT_IN_NANSD128:
+    case CFN_BUILT_IN_NANSD64X:
       return fold_const_builtin_nan (type, arg, false);
 
     case CFN_REDUC_PLUS:
diff --git a/gcc/ginclude/float.h b/gcc/ginclude/float.h
index 91b7008a57f..150dfcde0a1 100644
--- a/gcc/ginclude/float.h
+++ b/gcc/ginclude/float.h
@@ -602,6 +602,23 @@ see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
 
 #endif /* __STDC_WANT_IEC_60559_DFP_EXT__ || C23.  */
 
+#ifdef __STDC_WANT_IEC_60559_TYPES_EXT__
+#undef DEC64X_MANT_DIG
+#define DEC64X_MANT_DIG	__DEC64X_MANT_DIG__
+#undef DEC64X_MIN_EXP
+#define DEC64X_MIN_EXP	__DEC64X_MIN_EXP__
+#undef DEC64X_MAX_EXP
+#define DEC64X_MAX_EXP	__DEC64X_MAX_EXP__
+#undef DEC64X_MAX
+#define DEC64X_MAX   __DEC64X_MAX__
+#undef DEC64X_EPSILON
+#define DEC64X_EPSILON	__DEC64X_EPSILON__
+#undef DEC64X_MIN
+#define DEC64X_MIN	__DEC64X_MIN__
+#undef DEC64X_TRUE_MIN
+#define DEC64X_TRUE_MIN      __DEC64X_SUBNORMAL_MIN__
+#endif /* __STDC_WANT_IEC_60559_TYPES_EXT__ */
+
 #if defined __STDC_VERSION__ && __STDC_VERSION__ > 201710L
 
 /* Infinity in type _Decimal32.  */
@@ -619,6 +636,10 @@ see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
 #define DEC64_SNAN	(__builtin_nansd64 (""))
 #undef DEC128_SNAN
 #define DEC128_SNAN	(__builtin_nansd128 (""))
+#ifdef __STDC_WANT_IEC_60559_TYPES_EXT__
+#undef DEC64X_SNAN
+#define DEC64X_SNAN	(__builtin_nansd64x (""))
+#endif /* __STDC_WANT_IEC_60559_TYPES_EXT__ */
 
 #endif /* C23 */
 
diff --git a/gcc/testsuite/gcc.dg/dfp/c11-decimal64x-1.c b/gcc/testsuite/gcc.dg/dfp/c11-decimal64x-1.c
new file mode 100644
index 00000000000..a7de8689136
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/dfp/c11-decimal64x-1.c
@@ -0,0 +1,7 @@
+/* Test that DFP constants and _Decimal64x keyword are diagnosed in C11 mode: -pedantic.  */
+/* { dg-do compile } */
+/* { dg-options "-std=c11 -pedantic" } */
+
+int a = (int) 1.1D64x; /* { dg-warning "C23 feature" } */
+int b = (int) 2.d64x; /* { dg-warning "C23 feature" } */
+_Decimal64x c = 1; /* { dg-warning "ISO C does not support decimal floating-point before C23" } */
diff --git a/gcc/testsuite/gcc.dg/dfp/c11-decimal64x-2.c b/gcc/testsuite/gcc.dg/dfp/c11-decimal64x-2.c
new file mode 100644
index 00000000000..ceb2efe77a9
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/dfp/c11-decimal64x-2.c
@@ -0,0 +1,7 @@
+/* Test that DFP constants and _Decimal64x keyword are diagnosed in C11 mode: -pedantic-errors.  */
+/* { dg-do compile } */
+/* { dg-options "-std=c11 -pedantic-errors" } */
+
+int a = (int) 1.1D64x; /* { dg-error "C23 feature" } */
+int b = (int) 2.d64x; /* { dg-error "C23 feature" } */
+_Decimal64x c = 1; /* { dg-error "ISO C does not support decimal floating-point before C23" } */
diff --git a/gcc/testsuite/gcc.dg/dfp/c23-decimal64x-1.c b/gcc/testsuite/gcc.dg/dfp/c23-decimal64x-1.c
new file mode 100644
index 00000000000..6a6f815df16
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/dfp/c23-decimal64x-1.c
@@ -0,0 +1,74 @@
+/* Test _Decimal64x in C23 mode.  */
+/* { dg-do run } */
+/* { dg-options "-std=c23 -pedantic-errors" } */
+
+int a = (int) 1.1D64x;
+int b = (int) 2.d64x;
+_Decimal64x c = 1;
+
+#define expr_has_type(e, t) _Generic (e, default : 0, t : 1)
+static_assert (expr_has_type (1.1D64x, _Decimal64x));
+static_assert (expr_has_type (2.d64x, _Decimal64x));
+static_assert (expr_has_type (.33D64x, _Decimal64x));
+static_assert (expr_has_type (2e1d64x, _Decimal64x));
+static_assert (expr_has_type (.3e2D64x, _Decimal64x));
+static_assert (expr_has_type (4.5e3d64x, _Decimal64x));
+static_assert (expr_has_type (5.e0D64x, _Decimal64x));
+static_assert (expr_has_type (1e+2d64x, _Decimal64x));
+static_assert (expr_has_type (1000e-3D64x, _Decimal64x));
+static_assert (expr_has_type (__DEC64X_MIN__, _Decimal64x));
+static_assert (expr_has_type (__DEC64X_MAX__, _Decimal64x));
+static_assert (expr_has_type (__DEC64X_EPSILON__, _Decimal64x));
+static_assert (expr_has_type (__DEC64X_SUBNORMAL_MIN__, _Decimal64x));
+#if __DEC64X_MANT_DIG__ == __DEC128_MANT_DIG__ \
+    && __DEC64X_MAX_EXP__ == __DEC128_MAX_EXP__
+static_assert (expr_has_type (1.1D32 + 1.1D64x, _Decimal64x));
+static_assert (expr_has_type (1.1D64 + 1.1D64x, _Decimal64x));
+static_assert (expr_has_type (1.1D64x + 1.1D64x, _Decimal64x));
+static_assert (expr_has_type (1.1D128 + 1.1D64x, _Decimal128));
+static_assert (expr_has_type (1 + 1.1D64x, _Decimal64x));
+static_assert (expr_has_type (1U + 1.1D64x, _Decimal64x));
+static_assert (expr_has_type (1L + 1.1D64x, _Decimal64x));
+static_assert (expr_has_type (1UL + 1.1D64x, _Decimal64x));
+static_assert (expr_has_type (1LL + 1.1D64x, _Decimal64x));
+static_assert (expr_has_type (1ULL + 1.1D64x, _Decimal64x));
+static_assert (expr_has_type (1.1D64x + 1.1D32, _Decimal64x));
+static_assert (expr_has_type (1.1D64x + 1.1D64, _Decimal64x));
+static_assert (expr_has_type (1.1D64x + 1.1D64x, _Decimal64x));
+static_assert (expr_has_type (1.1D64x + 1.1D128, _Decimal128));
+static_assert (expr_has_type (1.1D64x + 1, _Decimal64x));
+static_assert (expr_has_type (1.1D64x + 1U, _Decimal64x));
+static_assert (expr_has_type (1.1D64x + 1L, _Decimal64x));
+static_assert (expr_has_type (1.1D64x + 1UL, _Decimal64x));
+static_assert (expr_has_type (1.1D64x + 1LL, _Decimal64x));
+static_assert (expr_has_type (1.1D64x + 1ULL, _Decimal64x));
+#endif
+
+_Decimal64x
+foo (_Decimal64x x, _Decimal64x y)
+{
+  return x + y;
+}
+
+int
+main ()
+{
+#if __DEC64X_MANT_DIG__ == __DEC128_MANT_DIG__ \
+    && __DEC64X_MAX_EXP__ == __DEC128_MAX_EXP__
+  if (1.1D64x != 1.1dl
+      || 2.d64x != 2.dl
+      || .33D64x != .33dl
+      || 2e1d64x != 2e1dl
+      || .3e2D64x != .3e2dl
+      || 4.5e3d64x != 4.5e3dl
+      || 5.e0D64x != 5.e0dl
+      || 1e+2d64x != 1e+2dl
+      || 1000e-3D64x != 1000e-3dl
+      || __DEC64X_MIN__ != __DEC128_MIN__
+      || __DEC64X_MAX__ != __DEC128_MAX__
+      || __DEC64X_EPSILON__ != __DEC128_EPSILON__
+      || __DEC64X_SUBNORMAL_MIN__ != __DEC128_SUBNORMAL_MIN__
+      || foo (0.5d64x, 0.5D64x) != 1.D64x)
+    __builtin_abort ();
+#endif
+}
diff --git a/gcc/testsuite/gcc.dg/dfp/c23-decimal64x-2.c b/gcc/testsuite/gcc.dg/dfp/c23-decimal64x-2.c
new file mode 100644
index 00000000000..4326bde614d
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/dfp/c23-decimal64x-2.c
@@ -0,0 +1,7 @@
+/* Test that DFP constants and _Decimal64x keyword are accepted in C23 mode: compat warnings.  */
+/* { dg-do compile } */
+/* { dg-options "-std=c23 -Wc11-c23-compat" } */
+
+int a = (int) 1.1D64x; /* { dg-warning "C23 feature" } */
+int b = (int) 2.d64x; /* { dg-warning "C23 feature" } */
+_Decimal64x c = 1; /* { dg-warning "ISO C does not support decimal floating-point before C23" } */
diff --git a/gcc/testsuite/gcc.dg/dfp/c23-decimal64x-3.c b/gcc/testsuite/gcc.dg/dfp/c23-decimal64x-3.c
new file mode 100644
index 00000000000..12f5e13fdce
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/dfp/c23-decimal64x-3.c
@@ -0,0 +1,26 @@
+/* Test _Decimal64x in C23 mode - builtins.  */
+/* { dg-do run } */
+/* { dg-options "-std=c23 -pedantic-errors" } */
+
+_Decimal64x a = __builtin_infd64x ();
+_Decimal64x b = __builtin_nand64x ("");
+_Decimal64x c = __builtin_nansd64x ("");
+_Decimal64x d = -42.D64x;
+_Decimal64x e = 5.25d64x;
+
+int
+main ()
+{
+  if (__builtin_fabsd64x (-2.5d64x) != 2.5D64x
+      || __builtin_fabsd64x (42.25D64x) != 42.25d64x
+      || __builtin_fabsd64x (d) != 42.d64x
+      || __builtin_fabsd64x (e) != 5.25D64x
+      || __builtin_isinf (42.d64x)
+      || __builtin_isnan (0.d64x)
+      || !__builtin_isinf (__builtin_infd64x ())
+      || !__builtin_isnan (__builtin_nand64x (""))
+      /* || !__builtin_isinf (a) */
+      || !__builtin_isnan (b)
+      || !__builtin_isnan (c))
+    __builtin_abort ();
+}
diff --git a/gcc/testsuite/gcc.dg/dfp/c23-decimal64x-4.c b/gcc/testsuite/gcc.dg/dfp/c23-decimal64x-4.c
new file mode 100644
index 00000000000..c536ef96b7a
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/dfp/c23-decimal64x-4.c
@@ -0,0 +1,43 @@
+/* Test _Decimal64x in C23 mode - float.h macros.  */
+/* { dg-do run } */
+/* { dg-options "-std=c23 -pedantic-errors" } */
+
+#ifndef __STDC_WANT_IEC_60559_TYPES_EXT__
+#define __STDC_WANT_IEC_60559_TYPES_EXT__ 1
+#endif
+
+#include <float.h>
+
+#define expr_has_type(e, t) _Generic (e, default : 0, t : 1)
+static_assert (expr_has_type (DEC64X_MAX, _Decimal64x));
+static_assert (expr_has_type (DEC64X_MIN, _Decimal64x));
+static_assert (expr_has_type (DEC64X_EPSILON, _Decimal64x));
+static_assert (expr_has_type (DEC64X_TRUE_MIN, _Decimal64x));
+
+int
+main ()
+{
+#if __DEC64X_MANT_DIG__ == __DEC128_MANT_DIG__ \
+    && __DEC64X_MAX_EXP__ == __DEC128_MAX_EXP__
+  if (DEC64X_MANT_DIG != 34)
+    __builtin_abort ();
+
+  if (DEC64X_MIN_EXP != -6142)
+    __builtin_abort ();
+
+  if (DEC64X_MAX_EXP != 6145)
+    __builtin_abort ();
+
+  if (DEC64X_MAX != 9.999999999999999999999999999999999E6144D64x)
+    __builtin_abort ();
+
+  if (DEC64X_EPSILON != 1E-33D64x)
+    __builtin_abort ();
+  
+  if (DEC64X_MIN != 1E-6143D64x)
+    __builtin_abort ();
+
+  if (DEC64X_TRUE_MIN != 0.000000000000000000000000000000001E-6143D64x)
+    __builtin_abort ();
+#endif
+}
diff --git a/gcc/tree-core.h b/gcc/tree-core.h
index 2a91e7935ca..dd61ba3c23d 100644
--- a/gcc/tree-core.h
+++ b/gcc/tree-core.h
@@ -781,6 +781,7 @@ enum tree_index : unsigned {
   TI_DFLOAT32_TYPE,
   TI_DFLOAT64_TYPE,
   TI_DFLOAT128_TYPE,
+  TI_DFLOAT64X_TYPE,
 
   TI_VOID_LIST_NODE,
 
diff --git a/gcc/tree.cc b/gcc/tree.cc
index 113a669128b..7fd8abb3cfd 100644
--- a/gcc/tree.cc
+++ b/gcc/tree.cc
@@ -9698,6 +9698,11 @@ build_common_tree_nodes (bool signed_char)
       TYPE_PRECISION (dfloat128_type_node) = DECIMAL128_TYPE_SIZE;
       SET_TYPE_MODE (dfloat128_type_node, TDmode);
       layout_type (dfloat128_type_node);
+
+      dfloat64x_type_node = make_node (REAL_TYPE);
+      TYPE_PRECISION (dfloat64x_type_node) = DECIMAL128_TYPE_SIZE;
+      SET_TYPE_MODE (dfloat64x_type_node, TDmode);
+      layout_type (dfloat64x_type_node);
     }
 
   complex_integer_type_node = build_complex_type (integer_type_node, true);
diff --git a/gcc/tree.h b/gcc/tree.h
index 7ed6d20c2e9..56c0454a598 100644
--- a/gcc/tree.h
+++ b/gcc/tree.h
@@ -4537,6 +4537,7 @@ tree_strip_any_location_wrapper (tree exp)
 #define dfloat32_type_node              global_trees[TI_DFLOAT32_TYPE]
 #define dfloat64_type_node              global_trees[TI_DFLOAT64_TYPE]
 #define dfloat128_type_node             global_trees[TI_DFLOAT128_TYPE]
+#define dfloat64x_type_node		global_trees[TI_DFLOAT64X_TYPE]
 
 /* The fixed-point types.  */
 #define sat_short_fract_type_node       global_trees[TI_SAT_SFRACT_TYPE]
diff --git a/libcpp/expr.cc b/libcpp/expr.cc
index 685233797c8..d3127651786 100644
--- a/libcpp/expr.cc
+++ b/libcpp/expr.cc
@@ -102,9 +102,7 @@ interpret_float_suffix (cpp_reader *pfile, const uchar *s, size_t len)
      df, DF, d32, D32 - _Decimal32.
      dd, DD, d64, D64 - _Decimal64.
      dl, DL, d128, D128 - _Decimal128.
-
-     The dN and DN suffixes for _DecimalN, and dNx and DNx for
-     _DecimalNx, defined in TS 18661-3:2015, are not supported.
+     d64x, D64x - _Decimal64x.
 
      Fixed-point suffixes, from TR 18037:2008, are supported.  They
      consist of three parts, in order:
@@ -258,8 +256,13 @@ interpret_float_suffix (cpp_reader *pfile, const uchar *s, size_t len)
 	    {
 	      if (s[1] == '3' && s[2] == '2' && len == 2)
 		return CPP_N_DFLOAT | CPP_N_SMALL;
-	      if (s[1] == '6' && s[2] == '4' && len == 2)
-		return CPP_N_DFLOAT | CPP_N_MEDIUM;
+	      if (s[1] == '6' && s[2] == '4')
+		{
+		  if (len == 2)
+		    return CPP_N_DFLOAT | CPP_N_MEDIUM;
+		  if (len == 3 && s[3] == 'x')
+		    return CPP_N_DFLOAT | CPP_N_FLOATNX;
+		}
 	      if (s[1] == '1' && s[2] == '2' && len == 3 && s[3] == '8')
 		return CPP_N_DFLOAT | CPP_N_LARGE;
 	    }