libgcc: Add {unsigned ,}__int128 <-> _Decimal{32,64,128} conversion support [PR65833]

The following patch adds the missing
{unsigned ,}__int128 <-> _Decimal{32,64,128}
conversion support into libgcc.a on top of the _BitInt support
(doing it without that would be larger amount of code and I hope all
the targets which support __int128 will eventually support _BitInt,
after all it is a required part of C23) and because it is in libgcc.a
only, it doesn't hurt that much if it is added for some architectures
only in GCC 15.
Initially I thought about doing this on the compiler side, but doing
it on the library side seems to be easier and more -Os friendly.
The tests currently require bitint effective target, that can be
removed when all the int128 targets support bitint.

2023-11-09  Jakub Jelinek  <jakub@redhat.com>

	PR libgcc/65833
libgcc/
	* config/t-softfp (softfp_bid_list): Add
	{U,}TItype <-> _Decimal{32,64,128} conversions.
	* soft-fp/floattisd.c: New file.
	* soft-fp/floattidd.c: New file.
	* soft-fp/floattitd.c: New file.
	* soft-fp/floatuntisd.c: New file.
	* soft-fp/floatuntidd.c: New file.
	* soft-fp/floatuntitd.c: New file.
	* soft-fp/fixsdti.c: New file.
	* soft-fp/fixddti.c: New file.
	* soft-fp/fixtdti.c: New file.
	* soft-fp/fixunssdti.c: New file.
	* soft-fp/fixunsddti.c: New file.
	* soft-fp/fixunstdti.c: New file.
gcc/testsuite/
	* gcc.dg/dfp/int128-1.c: New test.
	* gcc.dg/dfp/int128-2.c: New test.
	* gcc.dg/dfp/int128-3.c: New test.
	* gcc.dg/dfp/int128-4.c: New test.

1 files changed, 53 insertions, 0 deletions

diff --git a/libgcc/soft-fp/floatuntidd.c b/libgcc/soft-fp/floatuntidd.c
new file mode 100644
index 0000000..ea4108f
--- /dev/null
+++ b/libgcc/soft-fp/floatuntidd.c
@@ -0,0 +1,53 @@
+/* Software floating-point emulation.
+   Convert a 128bit unsigned integer to _Decimal64.
+
+   Copyright (C) 2023 Free Software Foundation, Inc.
+
+This file is part of GCC.
+
+GCC is free software; you can redistribute it and/or modify it under
+the terms of the GNU General Public License as published by the Free
+Software Foundation; either version 3, or (at your option) any later
+version.
+
+GCC is distributed in the hope that it will be useful, but WITHOUT ANY
+WARRANTY; without even the implied warranty of MERCHANTABILITY or
+FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+for more details.
+
+Under Section 7 of GPL version 3, you are granted additional
+permissions described in the GCC Runtime Library Exception, version
+3.1, as published by the Free Software Foundation.
+
+You should have received a copy of the GNU General Public License and
+a copy of the GCC Runtime Library Exception along with this program;
+see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
+<http://www.gnu.org/licenses/>.  */
+
+#include "soft-fp.h"
+#include "bitint.h"
+
+#if defined(__BITINT_MAXWIDTH__) && defined(__SIZEOF_INT128__)
+extern _Decimal64 __bid_floatbitintdd (const UBILtype *, SItype);
+extern _Decimal64 __bid_floatunstidd (UTItype);
+
+_Decimal64
+__bid_floatunstidd (UTItype i)
+{
+  UBILtype ib[128 / BIL_TYPE_SIZE];
+#if BIL_TYPE_SIZE == 128
+  ib[0] = i;
+#elif BIL_TYPE_SIZE == 64
+  ib[BITINT_END (0, 1)] = i >> 64;
+  ib[BITINT_END (1, 0)] = i;
+#elif BIL_TYPE_SIZE == 32
+  ib[BITINT_END (0, 3)] = i >> 96;
+  ib[BITINT_END (1, 2)] = i >> 64;
+  ib[BITINT_END (2, 1)] = i >> 32;
+  ib[BITINT_END (3, 0)] = i;
+#else
+#error Unsupported UBILtype
+#endif
+  return __bid_floatbitintdd (ib, 128);
+}
+#endif