Import gcrypt public-key cryptography and implement signature checking.

grub-core/lib/libgcrypt/mpi/power/mpih-rshift.S

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+/* IBM POWER rshift
+ *
+ *      Copyright (C) 1992, 1994, 1999, 2002 Free Software Foundation, Inc.
+ *
+ * This file is part of Libgcrypt.
+ *
+ * Libgcrypt is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as
+ * published by the Free Software Foundation; either version 2.1 of
+ * the License, or (at your option) any later version.
+ *
+ * Libgcrypt 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 Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
+ */
+
+#include "sysdep.h"
+#include "asm-syntax.h"
+
+
+/*
+# INPUT PARAMETERS
+# res_ptr	r3
+# s_ptr 	r4
+# size		r5
+# cnt		r6
+*/
+
+	.toc
+	.extern _gcry_mpih_rshift[DS]
+	.extern ._gcry_mpih_rshift
+.csect [PR]
+	.align 2
+	.globl _gcry_mpih_rshift
+	.globl ._gcry_mpih_rshift
+	.csect _gcry_mpih_rshift[DS]
+_gcry_mpih_rshift:
+	.long ._gcry_mpih_rshift, TOC[tc0], 0
+	.csect [PR]
+._gcry_mpih_rshift:
+	sfi	8,6,32
+	mtctr	5		# put limb count in CTR loop register
+	l	0,0(4)		# read least significant limb
+	ai	9,3,-4		# adjust res_ptr since it's offset in the stu:s
+	sle	3,0,8		# compute carry limb, and init MQ register
+	bdz	Lend2		# if just one limb, skip loop
+	lu	0,4(4)		# read 2:nd least significant limb
+	sleq	7,0,8		# compute least significant limb of result
+	bdz	Lend		# if just two limb, skip loop
+Loop:	lu	0,4(4)		# load next higher limb
+	stu	7,4(9)		# store previous result during read latency
+	sleq	7,0,8		# compute result limb
+	bdn	Loop		# loop back until CTR is zero
+Lend:	stu	7,4(9)		# store 2:nd most significant limb
+Lend2:	sre	7,0,6		# compute most significant limb
+	st	7,4(9)		# store it
+	br
+
+