arm: Add optimized submul_1

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.

diff --git a/ports/ChangeLog.arm b/ports/ChangeLog.arm
index a701215..9470af2 100644 (file)
--- a/ports/ChangeLog.arm
+++ b/ports/ChangeLog.arm
@@ -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.

diff --git a/ports/sysdeps/arm/submul_1.S b/ports/sysdeps/arm/submul_1.S
new file mode 100644 (file)
index 0000000..3805eca
--- /dev/null
+++ b/ports/sysdeps/arm/submul_1.S
@@ -0,0 +1,68 @@
+/* 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)