Import gcrypt public-key cryptography and implement signature checking.

grub-core/lib/libgcrypt/mpi/amd64/mpih-sub1.S

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+/* AMD64 (x86_64) sub_n -- Subtract two limb vectors of the same length > 0 and store
+ *		   sum in a third limb vector.
+ *
+ *      Copyright (C) 1992, 1994, 1995, 1998, 
+ *                    2001, 2002, 2006 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
+ *
+ * Note: This code is heavily based on the GNU MP Library.
+ *	 Actually it's the same code with only minor changes in the
+ *	 way the data is stored; this is to support the abstraction
+ *	 of an optional secure memory allocation which may be used
+ *	 to avoid revealing of sensitive data due to paging etc.
+ */
+
+
+#include "sysdep.h"
+#include "asm-syntax.h"
+
+
+/*******************
+ *  mpi_limb_t
+ *  _gcry_mpih_sub_n( mpi_ptr_t res_ptr,	rdi
+ *		   mpi_ptr_t s1_ptr,		rsi
+ *		   mpi_ptr_t s2_ptr,		rdx
+ *		   mpi_size_t size)		rcx
+ */
+.text
+	.globl C_SYMBOL_NAME(_gcry_mpih_sub_n)
+C_SYMBOL_NAME(_gcry_mpih_sub_n:)
+	leaq	(%rsi,%rcx,8), %rsi
+	leaq	(%rdi,%rcx,8), %rdi
+	leaq	(%rdx,%rcx,8), %rdx
+	negq	%rcx
+	xorl	%eax, %eax		/* clear cy */
+
+	ALIGN(4)			/* minimal alignment for claimed speed */
+.Loop:	movq	(%rsi,%rcx,8), %rax
+	movq	(%rdx,%rcx,8), %r10
+	sbbq	%r10, %rax
+	movq	%rax, (%rdi,%rcx,8)
+	incq	%rcx
+	jne	.Loop
+
+	movq	%rcx, %rax		/* zero %rax */
+	adcq	%rax, %rax
+	ret