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arm: Add optimized submul_1

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Written from scratch rather than copied from GMP, due to LGPL 2.1 vs
GPL 3, but tested with the GMP testsuite.

This is 50% faster than the generic code as measured on Cortex-A15.
It is 25% slower than the current GMP routine on the same core.
This commit is contained in:
Richard Henderson 2013-02-26 15:49:51 -08:00
parent 21e31515a6
commit fe62ba37a3
2 changed files with 69 additions and 0 deletions
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1
ports/ChangeLog.arm
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@ -1,5 +1,6 @@
2013-03-06 Richard Henderson <rth@redhat.com>
* sysdeps/arm/submul_1.S: New file.
* sysdeps/arm/addmul_1.S: New file.
* sysdeps/arm/armv6t2/ffs.S: New file.
* sysdeps/arm/armv6t2/ffsll.S: New file.

68
ports/sysdeps/arm/submul_1.S Normal file
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/* mpn_submul_1 -- multiply and subtract bignums.
Copyright (C) 2013 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C 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 2.1 of the License, or (at your option) any later version.
The GNU C 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 C Library. If not, see
<http://www.gnu.org/licenses/>. */
#include <sysdep.h>
.syntax unified
.text
@ cycles/limb
@ StrongArm ?
@ Cortex-A8 ?
@ Cortex-A9 ?
@ Cortex-A15 4
/* mp_limb_t mpn_submul_1(res_ptr, src1_ptr, size, s2_limb) */
ENTRY (__mpn_submul_1)
push { r4, r5, r6, r7 }
cfi_adjust_cfa_offset (16)
cfi_rel_offset (r4, 0)
cfi_rel_offset (r5, 4)
cfi_rel_offset (r6, 8)
cfi_rel_offset (r7, 12)
ldr r6, [r1], #4
ldr r7, [r0]
mov r4, #0 /* init carry in */
b 1f
0:
ldr r6, [r1], #4 /* load next ul */
adds r5, r5, r4 /* (lpl, c) = lpl + cl */
adc r4, ip, #0 /* cl = hpl + c */
subs r5, r7, r5 /* (lpl, !c) = rl - lpl */
ldr r7, [r0, #4] /* load next rl */
it cc
addcc r4, r4, #1 /* cl += !c */
str r5, [r0], #4
1:
umull r5, ip, r6, r3 /* (hpl, lpl) = ul * vl */
subs r2, r2, #1
bne 0b
adds r5, r5, r4 /* (lpl, c) = lpl + cl */
adc r4, ip, #0 /* cl = hpl + c */
subs r5, r7, r5 /* (lpl, !c) = rl - lpl */
str r5, [r0], #4
it cc
addcc r4, r4, #1 /* cl += !c */
mov r0, r4 /* return carry */
pop { r4, r5, r6, r7 }
DO_RET (lr)
END (__mpn_submul_1)