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diff --git a/mpn/riscv/64/sec_tabselect.asm b/mpn/riscv/64/sec_tabselect.asm
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+++ b/mpn/riscv/64/sec_tabselect.asm
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+dnl  RISC-V/64 mpn_sec_tabselect
+
+dnl  Copyright 2021 Free Software Foundation, Inc.
+
+dnl  This file is part of the GNU MP Library.
+dnl
+dnl  The GNU MP Library is free software; you can redistribute it and/or modify
+dnl  it under the terms of either:
+dnl
+dnl    * the GNU Lesser General Public License as published by the Free
+dnl      Software Foundation; either version 3 of the License, or (at your
+dnl      option) any later version.
+dnl
+dnl  or
+dnl
+dnl    * the GNU General Public License as published by the Free Software
+dnl      Foundation; either version 2 of the License, or (at your option) any
+dnl      later version.
+dnl
+dnl  or both in parallel, as here.
+dnl
+dnl  The GNU MP Library is distributed in the hope that it will be useful, but
+dnl  WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+dnl  or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+dnl  for more details.
+dnl
+dnl  You should have received copies of the GNU General Public License and the
+dnl  GNU Lesser General Public License along with the GNU MP Library.  If not,
+dnl  see https://www.gnu.org/licenses/.
+
+include(`../config.m4')
+
+dnl This is compiler output, mildly edited.  We don't expect this to be faster
+dnl than the C fallback code, but providing this in assembly avoids problems
+dnl with compilers which generate side channel leaky code.
+
+define(`rp',	`a0')
+define(`tp',	`a1')
+define(`n',	`a2')
+define(`nents',	`a3')
+define(`which',	`a4')
+
+ASM_START()
+PROLOGUE(mpn_sec_tabselect)
+	slli	n, n, 3
+	add	t4, a0, n
+
+L(cpy):	ld	a7, 0(tp)
+	addi	tp, tp, 8
+	addi	rp, rp, 8
+	sd	a7, -8(rp)
+	bne	rp, t4, L(cpy)
+
+	li	t5, 1
+	ble	nents, t5, L(ret)
+
+L(outer):
+	xor	t3, which, t5
+	neg	t3, t3
+	srai	t3, t3, 63
+	sub	rp, rp, n
+
+L(top):	ld	a5, 0(rp)
+	ld	t1, 0(tp)
+	addi	rp, rp, 8
+	addi	tp, tp, 8
+	xor	a5, a5, t1
+	and	a5, a5, t3
+	xor	a5, a5, t1
+	sd	a5, -8(rp)
+	bne	t4, rp, L(top)
+
+	addi	t5, t5, 1
+	bne	nents, t5, L(outer)
+
+L(ret):	ret
+EPILOGUE()