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diff --git a/gmp/mpn/thumb/sub_n.s b/gmp/mpn/thumb/sub_n.s
new file mode 100644
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+@ ARM/Thumb mpn_sub_n -- Subtract two limb vectors of the same length > 0 and
+@ store difference in a third limb vector.
+
+@ Copyright 1997, 2000 Free Software Foundation, Inc.
+
+@ This file is part of the GNU MP Library.
+
+@ The GNU MP Library 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 3 of the License, or (at your
+@ option) any later version.
+
+@ The GNU MP Library 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 the GNU MP Library.  If not, see http://www.gnu.org/licenses/.
+
+
+@ INPUT PARAMETERS
+@ RES_ptr	r0
+@ S1_ptr	r1
+@ S2_ptr	r2
+@ SIZE		r3
+
+@ NOT TESTED CODE
+
+	.text
+	.thumb
+	.align	0
+	.global	___gmpn_sub_n
+___gmpn_sub_n:
+	push	{r4, r5, r6, lr}
+	mov	r6, #1			@ init carry save register
+
+Loop:	sub	r6, #1			@ restore carry (set iff r6 was 0)
+	ldmia	r1!, {r4}		@ load next limb from S1
+	ldmia	r2!, {r5}		@ load next limb from S2
+	sbc	r4, r5
+	stmia	r0!, {r4}		@ store result limb to RES
+	sbc	r6, r6			@ save negated carry
+	sub	r3, #1
+	bge	Loop			@ loop back while remaining count >= 4
+
+	mov	r0, r6
+	pop	{r4, r5, r6, pc}