Add ARMv8 optimized string handling functions based on cortex-strings
This adds ARMv8 optimized string handling functions to Bionic.
The implementations live in a generic/ directory because there will
likely be more CPU specific versions (e.g. Cortex-A53 vs. Cortex-A57)
later.
These implementations are 50%+ faster on current v8 models.
Change-Id: If3adc54a284d9519459b0d4d4390f0cd6ded8786
Signed-off-by: Bernhard Rosenkraenzer <Bernhard.Rosenkranzer@linaro.org>
diff --git a/libc/arch-arm64/generic/bionic/strcmp.S b/libc/arch-arm64/generic/bionic/strcmp.S
new file mode 100644
index 0000000..3cce478
--- /dev/null
+++ b/libc/arch-arm64/generic/bionic/strcmp.S
@@ -0,0 +1,162 @@
+/* Copyright (c) 2012, Linaro Limited
+ All rights reserved.
+
+ Redistribution and use in source and binary forms, with or without
+ modification, are permitted provided that the following conditions are met:
+ * Redistributions of source code must retain the above copyright
+ notice, this list of conditions and the following disclaimer.
+ * Redistributions in binary form must reproduce the above copyright
+ notice, this list of conditions and the following disclaimer in the
+ documentation and/or other materials provided with the distribution.
+ * Neither the name of the Linaro nor the
+ names of its contributors may be used to endorse or promote products
+ derived from this software without specific prior written permission.
+
+ THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+*/
+
+/* Assumptions:
+ *
+ * ARMv8-a, AArch64
+ */
+
+#include <private/bionic_asm.h>
+
+#define REP8_01 0x0101010101010101
+#define REP8_7f 0x7f7f7f7f7f7f7f7f
+#define REP8_80 0x8080808080808080
+
+/* Parameters and result. */
+#define src1 x0
+#define src2 x1
+#define result x0
+
+/* Internal variables. */
+#define data1 x2
+#define data1w w2
+#define data2 x3
+#define data2w w3
+#define has_nul x4
+#define diff x5
+#define syndrome x6
+#define tmp1 x7
+#define tmp2 x8
+#define tmp3 x9
+#define zeroones x10
+#define pos x11
+
+ /* Start of performance-critical section -- one 64B cache line. */
+ENTRY(strcmp)
+ eor tmp1, src1, src2
+ mov zeroones, #REP8_01
+ tst tmp1, #7
+ b.ne .Lmisaligned8
+ ands tmp1, src1, #7
+ b.ne .Lmutual_align
+ /* NUL detection works on the principle that (X - 1) & (~X) & 0x80
+ (=> (X - 1) & ~(X | 0x7f)) is non-zero iff a byte is zero, and
+ can be done in parallel across the entire word. */
+.Lloop_aligned:
+ ldr data1, [src1], #8
+ ldr data2, [src2], #8
+.Lstart_realigned:
+ sub tmp1, data1, zeroones
+ orr tmp2, data1, #REP8_7f
+ eor diff, data1, data2 /* Non-zero if differences found. */
+ bic has_nul, tmp1, tmp2 /* Non-zero if NUL terminator. */
+ orr syndrome, diff, has_nul
+ cbz syndrome, .Lloop_aligned
+ /* End of performance-critical section -- one 64B cache line. */
+
+#ifndef __AARCH64EB__
+ rev syndrome, syndrome
+ rev data1, data1
+ /* The MS-non-zero bit of the syndrome marks either the first bit
+ that is different, or the top bit of the first zero byte.
+ Shifting left now will bring the critical information into the
+ top bits. */
+ clz pos, syndrome
+ rev data2, data2
+ lsl data1, data1, pos
+ lsl data2, data2, pos
+ /* But we need to zero-extend (char is unsigned) the value and then
+ perform a signed 32-bit subtraction. */
+ lsr data1, data1, #56
+ sub result, data1, data2, lsr #56
+ ret
+#else
+ /* For big-endian we cannot use the trick with the syndrome value
+ as carry-propagation can corrupt the upper bits if the trailing
+ bytes in the string contain 0x01. */
+ /* However, if there is no NUL byte in the dword, we can generate
+ the result directly. We can't just subtract the bytes as the
+ MSB might be significant. */
+ cbnz has_nul, 1f
+ cmp data1, data2
+ cset result, ne
+ cneg result, result, lo
+ ret
+1:
+ /* Re-compute the NUL-byte detection, using a byte-reversed value. */
+ rev tmp3, data1
+ sub tmp1, tmp3, zeroones
+ orr tmp2, tmp3, #REP8_7f
+ bic has_nul, tmp1, tmp2
+ rev has_nul, has_nul
+ orr syndrome, diff, has_nul
+ clz pos, syndrome
+ /* The MS-non-zero bit of the syndrome marks either the first bit
+ that is different, or the top bit of the first zero byte.
+ Shifting left now will bring the critical information into the
+ top bits. */
+ lsl data1, data1, pos
+ lsl data2, data2, pos
+ /* But we need to zero-extend (char is unsigned) the value and then
+ perform a signed 32-bit subtraction. */
+ lsr data1, data1, #56
+ sub result, data1, data2, lsr #56
+ ret
+#endif
+
+.Lmutual_align:
+ /* Sources are mutually aligned, but are not currently at an
+ alignment boundary. Round down the addresses and then mask off
+ the bytes that preceed the start point. */
+ bic src1, src1, #7
+ bic src2, src2, #7
+ lsl tmp1, tmp1, #3 /* Bytes beyond alignment -> bits. */
+ ldr data1, [src1], #8
+ neg tmp1, tmp1 /* Bits to alignment -64. */
+ ldr data2, [src2], #8
+ mov tmp2, #~0
+#ifdef __AARCH64EB__
+ /* Big-endian. Early bytes are at MSB. */
+ lsl tmp2, tmp2, tmp1 /* Shift (tmp1 & 63). */
+#else
+ /* Little-endian. Early bytes are at LSB. */
+ lsr tmp2, tmp2, tmp1 /* Shift (tmp1 & 63). */
+#endif
+ orr data1, data1, tmp2
+ orr data2, data2, tmp2
+ b .Lstart_realigned
+
+.Lmisaligned8:
+ /* We can do better than this. */
+ ldrb data1w, [src1], #1
+ ldrb data2w, [src2], #1
+ cmp data1w, #1
+ ccmp data1w, data2w, #0, cs /* NZCV = 0b0000. */
+ b.eq .Lmisaligned8
+ sub result, data1, data2
+ ret
+END(strcmp)