[AArch64] Add optimized strchrnul.

Here is an optimized implementation of __strchrnul.  The
simplification that we don't have to track precisely why the loop
terminates (match or end-of-string) means we have to do less work in
both setup and the core inner loop.  That means this should never be
slower than strchr.

As with strchr, the use of LD1 means we do not need different versions
for big-/little-endian.

diff --git a/ChangeLog b/ChangeLog
index 0929cb6a245d8c163d611578b2e9d0e97a33bd7d..51469e1056db484ae6ac98c69122b0a23dbd4bd3 100644 (file)
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+2014-11-05  Richard Earnshaw  <rearnsha@arm.com>
+
+       * sysdeps/aarch64/strchrnul.S: New file.
+
 2014-11-05  Adhemerval Zanella  <azanella@linux.vnet.ibm.com>
 
        * sysdeps/powerpc/powerpc64/power8/memset.S (MTVSRD_V1_R4): Simplify

diff --git a/NEWS b/NEWS
index 382d38dbdfd322cf66d0984f1e24279c6981435c..4656531663f03f472f16ea05b62d592410c69967 100644 (file)
--- a/NEWS
+++ b/NEWS
@@ -32,6 +32,8 @@ Version 2.20
   17084, 17086, 17088, 17092, 17097, 17125, 17135, 17137, 17150, 17153,
   17187, 17213, 17259, 17261, 17262, 17263, 17319, 17325, 17354.
 
+* Optimized strchrnul implementation for AArch64.  Contributed by ARM Ltd.
+
 * Reverted change of ABI data structures for s390 and s390x:
   On s390 and s390x the size of struct ucontext and jmp_buf was increased in
   2.19. This change is reverted in 2.20. The introduced 2.19 symbol versions

diff --git a/sysdeps/aarch64/strchrnul.S b/sysdeps/aarch64/strchrnul.S
new file mode 100644 (file)
index 0000000..b98c2e9
--- /dev/null
+++ b/sysdeps/aarch64/strchrnul.S
@@ -0,0 +1,130 @@
+/* strchrnul - find a character or nul in a string
+
+   Copyright (C) 2014 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>
+
+/* Assumptions:
+ *
+ * ARMv8-a, AArch64
+ * Neon Available.
+ */
+
+/* Arguments and results.  */
+#define srcin          x0
+#define chrin          w1
+
+#define result         x0
+
+/* Locals and temporaries.  */
+
+#define src            x2
+#define tmp1           x3
+#define wtmp2          w4
+#define tmp3           x5
+
+#define vrepchr                v0
+#define vdata1         v1
+#define vdata2         v2
+#define vhas_nul1      v3
+#define vhas_nul2      v4
+#define vhas_chr1      v5
+#define vhas_chr2      v6
+#define vrepmask       v15
+#define vend1          v16
+
+/* Core algorithm.
+
+   For each 32-byte hunk we calculate a 64-bit syndrome value, with
+   two bits per byte (LSB is always in bits 0 and 1, for both big
+   and little-endian systems).  For each tuple, bit 0 is set iff
+   the relevant byte matched the requested character or nul.  Since the
+   bits in the syndrome reflect exactly the order in which things occur
+   in the original string a count_trailing_zeros() operation will
+   identify exactly which byte is causing the termination.  */
+
+ENTRY (__strchrnul)
+       /* Magic constant 0x40100401 to allow us to identify which lane
+          matches the termination condition.  */
+       mov     wtmp2, #0x0401
+       movk    wtmp2, #0x4010, lsl #16
+       dup     vrepchr.16b, chrin
+       bic     src, srcin, #31         /* Work with aligned 32-byte hunks.  */
+       dup     vrepmask.4s, wtmp2
+       ands    tmp1, srcin, #31
+       b.eq    L(loop)
+
+       /* Input string is not 32-byte aligned.  Rather than forcing
+          the padding bytes to a safe value, we calculate the syndrome
+          for all the bytes, but then mask off those bits of the
+          syndrome that are related to the padding.  */
+       ld1     {vdata1.16b, vdata2.16b}, [src], #32
+       neg     tmp1, tmp1
+       cmeq    vhas_nul1.16b, vdata1.16b, #0
+       cmeq    vhas_chr1.16b, vdata1.16b, vrepchr.16b
+       cmeq    vhas_nul2.16b, vdata2.16b, #0
+       cmeq    vhas_chr2.16b, vdata2.16b, vrepchr.16b
+       orr     vhas_chr1.16b, vhas_chr1.16b, vhas_nul1.16b
+       orr     vhas_chr2.16b, vhas_chr2.16b, vhas_nul2.16b
+       and     vhas_chr1.16b, vhas_chr1.16b, vrepmask.16b
+       and     vhas_chr2.16b, vhas_chr2.16b, vrepmask.16b
+       lsl     tmp1, tmp1, #1
+       addp    vend1.16b, vhas_chr1.16b, vhas_chr2.16b // 256->128
+       mov     tmp3, #~0
+       addp    vend1.16b, vend1.16b, vend1.16b         // 128->64
+       lsr     tmp1, tmp3, tmp1
+
+       mov     tmp3, vend1.2d[0]
+       bic     tmp1, tmp3, tmp1        // Mask padding bits.
+       cbnz    tmp1, L(tail)
+
+L(loop):
+       ld1     {vdata1.16b, vdata2.16b}, [src], #32
+       cmeq    vhas_nul1.16b, vdata1.16b, #0
+       cmeq    vhas_chr1.16b, vdata1.16b, vrepchr.16b
+       cmeq    vhas_nul2.16b, vdata2.16b, #0
+       cmeq    vhas_chr2.16b, vdata2.16b, vrepchr.16b
+       /* Use a fast check for the termination condition.  */
+       orr     vhas_chr1.16b, vhas_nul1.16b, vhas_chr1.16b
+       orr     vhas_chr2.16b, vhas_nul2.16b, vhas_chr2.16b
+       orr     vend1.16b, vhas_chr1.16b, vhas_chr2.16b
+       addp    vend1.2d, vend1.2d, vend1.2d
+       mov     tmp1, vend1.2d[0]
+       cbz     tmp1, L(loop)
+
+       /* Termination condition found.  Now need to establish exactly why
+          we terminated.  */
+       and     vhas_chr1.16b, vhas_chr1.16b, vrepmask.16b
+       and     vhas_chr2.16b, vhas_chr2.16b, vrepmask.16b
+       addp    vend1.16b, vhas_chr1.16b, vhas_chr2.16b         // 256->128
+       addp    vend1.16b, vend1.16b, vend1.16b         // 128->64
+
+       mov     tmp1, vend1.2d[0]
+L(tail):
+       /* Count the trailing zeros, by bit reversing...  */
+       rbit    tmp1, tmp1
+       /* Re-bias source.  */
+       sub     src, src, #32
+       clz     tmp1, tmp1      /* ... and counting the leading zeros.  */
+       /* tmp1 is twice the offset into the fragment.  */
+       add     result, src, tmp1, lsr #1
+       ret
+
+END(__strchrnul)
+weak_alias (__strchrnul, strchrnul)