arm64: lib: Implement optimized string length routines

This patch, based on Linaro's Cortex Strings library, adds
an assembly optimized strlen() and strnlen() functions.

Signed-off-by: Zhichang Yuan <zhichang.yuan@linaro.org>
Signed-off-by: Deepak Saxena <dsaxena@linaro.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

3 files changed, 299 insertions, 1 deletions

diff --git a/arch/arm64/lib/Makefile b/arch/arm64/lib/Makefile
index aaaf6180c558..d98d3e39879e 100644
--- a/arch/arm64/lib/Makefile
+++ b/arch/arm64/lib/Makefile
@@ -1,4 +1,5 @@
 lib-y           := bitops.o clear_user.o delay.o copy_from_user.o       \
                    copy_to_user.o copy_in_user.o copy_page.o            \
                    clear_page.o memchr.o memcpy.o memmove.o memset.o    \
-                   memcmp.o strcmp.o strncmp.o strchr.o strrchr.o
+                   memcmp.o strcmp.o strncmp.o strlen.o strnlen.o       \
+                   strchr.o strrchr.o
diff --git a/arch/arm64/lib/strlen.S b/arch/arm64/lib/strlen.S
new file mode 100644
index 000000000000..987b68b9ce44
--- /dev/null
+++ b/arch/arm64/lib/strlen.S
@@ -0,0 +1,126 @@
+/*
+ * Copyright (C) 2013 ARM Ltd.
+ * Copyright (C) 2013 Linaro.
+ *
+ * This code is based on glibc cortex strings work originally authored by Linaro
+ * and re-licensed under GPLv2 for the Linux kernel. The original code can
+ * be found @
+ *
+ * http://bazaar.launchpad.net/~linaro-toolchain-dev/cortex-strings/trunk/
+ * files/head:/src/aarch64/
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <linux/linkage.h>
+#include <asm/assembler.h>
+
+/*
+ * calculate the length of a string
+ *
+ * Parameters:
+ *      x0 - const string pointer
+ * Returns:
+ *      x0 - the return length of specific string
+ */
+
+/* Arguments and results.  */
+srcin           .req    x0
+len             .req    x0
+
+/* Locals and temporaries.  */
+src             .req    x1
+data1           .req    x2
+data2           .req    x3
+data2a          .req    x4
+has_nul1        .req    x5
+has_nul2        .req    x6
+tmp1            .req    x7
+tmp2            .req    x8
+tmp3            .req    x9
+tmp4            .req    x10
+zeroones        .req    x11
+pos             .req    x12
+
+#define REP8_01 0x0101010101010101
+#define REP8_7f 0x7f7f7f7f7f7f7f7f
+#define REP8_80 0x8080808080808080
+
+ENTRY(strlen)
+        mov     zeroones, #REP8_01
+        bic     src, srcin, #15
+        ands    tmp1, srcin, #15
+        b.ne    .Lmisaligned
+        /*
+        * 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.
+        */
+        /*
+        * The inner loop deals with two Dwords at a time. This has a
+        * slightly higher start-up cost, but we should win quite quickly,
+        * especially on cores with a high number of issue slots per
+        * cycle, as we get much better parallelism out of the operations.
+        */
+.Lloop:
+        ldp     data1, data2, [src], #16
+.Lrealigned:
+        sub     tmp1, data1, zeroones
+        orr     tmp2, data1, #REP8_7f
+        sub     tmp3, data2, zeroones
+        orr     tmp4, data2, #REP8_7f
+        bic     has_nul1, tmp1, tmp2
+        bics    has_nul2, tmp3, tmp4
+        ccmp    has_nul1, #0, #0, eq    /* NZCV = 0000  */
+        b.eq    .Lloop
+
+        sub     len, src, srcin
+        cbz     has_nul1, .Lnul_in_data2
+CPU_BE( mov     data2, data1 )  /*prepare data to re-calculate the syndrome*/
+        sub     len, len, #8
+        mov     has_nul2, has_nul1
+.Lnul_in_data2:
+        /*
+        * For big-endian, carry propagation (if the final byte in the
+        * string is 0x01) means we cannot use has_nul directly.  The
+        * easiest way to get the correct byte is to byte-swap the data
+        * and calculate the syndrome a second time.
+        */
+CPU_BE( rev     data2, data2 )
+CPU_BE( sub     tmp1, data2, zeroones )
+CPU_BE( orr     tmp2, data2, #REP8_7f )
+CPU_BE( bic     has_nul2, tmp1, tmp2 )
+
+        sub     len, len, #8
+        rev     has_nul2, has_nul2
+        clz     pos, has_nul2
+        add     len, len, pos, lsr #3           /* Bits to bytes.  */
+        ret
+
+.Lmisaligned:
+        cmp     tmp1, #8
+        neg     tmp1, tmp1
+        ldp     data1, data2, [src], #16
+        lsl     tmp1, tmp1, #3          /* Bytes beyond alignment -> bits.  */
+        mov     tmp2, #~0
+        /* Big-endian.  Early bytes are at MSB.  */
+CPU_BE( lsl     tmp2, tmp2, tmp1 )      /* Shift (tmp1 & 63).  */
+        /* Little-endian.  Early bytes are at LSB.  */
+CPU_LE( lsr     tmp2, tmp2, tmp1 )      /* Shift (tmp1 & 63).  */
+
+        orr     data1, data1, tmp2
+        orr     data2a, data2, tmp2
+        csinv   data1, data1, xzr, le
+        csel    data2, data2, data2a, le
+        b       .Lrealigned
+ENDPROC(strlen)
diff --git a/arch/arm64/lib/strnlen.S b/arch/arm64/lib/strnlen.S
new file mode 100644
index 000000000000..2ca665711bf2
--- /dev/null
+++ b/arch/arm64/lib/strnlen.S
@@ -0,0 +1,171 @@
+/*
+ * Copyright (C) 2013 ARM Ltd.
+ * Copyright (C) 2013 Linaro.
+ *
+ * This code is based on glibc cortex strings work originally authored by Linaro
+ * and re-licensed under GPLv2 for the Linux kernel. The original code can
+ * be found @
+ *
+ * http://bazaar.launchpad.net/~linaro-toolchain-dev/cortex-strings/trunk/
+ * files/head:/src/aarch64/
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <linux/linkage.h>
+#include <asm/assembler.h>
+
+/*
+ * determine the length of a fixed-size string
+ *
+ * Parameters:
+ *      x0 - const string pointer
+ *      x1 - maximal string length
+ * Returns:
+ *      x0 - the return length of specific string
+ */
+
+/* Arguments and results.  */
+srcin           .req    x0
+len             .req    x0
+limit           .req    x1
+
+/* Locals and temporaries.  */
+src             .req    x2
+data1           .req    x3
+data2           .req    x4
+data2a          .req    x5
+has_nul1        .req    x6
+has_nul2        .req    x7
+tmp1            .req    x8
+tmp2            .req    x9
+tmp3            .req    x10
+tmp4            .req    x11
+zeroones        .req    x12
+pos             .req    x13
+limit_wd        .req    x14
+
+#define REP8_01 0x0101010101010101
+#define REP8_7f 0x7f7f7f7f7f7f7f7f
+#define REP8_80 0x8080808080808080
+
+ENTRY(strnlen)
+        cbz     limit, .Lhit_limit
+        mov     zeroones, #REP8_01
+        bic     src, srcin, #15
+        ands    tmp1, srcin, #15
+        b.ne    .Lmisaligned
+        /* Calculate the number of full and partial words -1.  */
+        sub     limit_wd, limit, #1 /* Limit != 0, so no underflow.  */
+        lsr     limit_wd, limit_wd, #4  /* Convert to Qwords.  */
+
+        /*
+        * 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.
+        */
+        /*
+        * The inner loop deals with two Dwords at a time.  This has a
+        * slightly higher start-up cost, but we should win quite quickly,
+        * especially on cores with a high number of issue slots per
+        * cycle, as we get much better parallelism out of the operations.
+        */
+.Lloop:
+        ldp     data1, data2, [src], #16
+.Lrealigned:
+        sub     tmp1, data1, zeroones
+        orr     tmp2, data1, #REP8_7f
+        sub     tmp3, data2, zeroones
+        orr     tmp4, data2, #REP8_7f
+        bic     has_nul1, tmp1, tmp2
+        bic     has_nul2, tmp3, tmp4
+        subs    limit_wd, limit_wd, #1
+        orr     tmp1, has_nul1, has_nul2
+        ccmp    tmp1, #0, #0, pl    /* NZCV = 0000  */
+        b.eq    .Lloop
+
+        cbz     tmp1, .Lhit_limit   /* No null in final Qword.  */
+
+        /*
+        * We know there's a null in the final Qword. The easiest thing
+        * to do now is work out the length of the string and return
+        * MIN (len, limit).
+        */
+        sub     len, src, srcin
+        cbz     has_nul1, .Lnul_in_data2
+CPU_BE( mov     data2, data1 )  /*perpare data to re-calculate the syndrome*/
+
+        sub     len, len, #8
+        mov     has_nul2, has_nul1
+.Lnul_in_data2:
+        /*
+        * For big-endian, carry propagation (if the final byte in the
+        * string is 0x01) means we cannot use has_nul directly.  The
+        * easiest way to get the correct byte is to byte-swap the data
+        * and calculate the syndrome a second time.
+        */
+CPU_BE( rev     data2, data2 )
+CPU_BE( sub     tmp1, data2, zeroones )
+CPU_BE( orr     tmp2, data2, #REP8_7f )
+CPU_BE( bic     has_nul2, tmp1, tmp2 )
+
+        sub     len, len, #8
+        rev     has_nul2, has_nul2
+        clz     pos, has_nul2
+        add     len, len, pos, lsr #3       /* Bits to bytes.  */
+        cmp     len, limit
+        csel    len, len, limit, ls     /* Return the lower value.  */
+        ret
+
+.Lmisaligned:
+        /*
+        * Deal with a partial first word.
+        * We're doing two things in parallel here;
+        * 1) Calculate the number of words (but avoiding overflow if
+        * limit is near ULONG_MAX) - to do this we need to work out
+        * limit + tmp1 - 1 as a 65-bit value before shifting it;
+        * 2) Load and mask the initial data words - we force the bytes
+        * before the ones we are interested in to 0xff - this ensures
+        * early bytes will not hit any zero detection.
+        */
+        ldp     data1, data2, [src], #16
+
+        sub     limit_wd, limit, #1
+        and     tmp3, limit_wd, #15
+        lsr     limit_wd, limit_wd, #4
+
+        add     tmp3, tmp3, tmp1
+        add     limit_wd, limit_wd, tmp3, lsr #4
+
+        neg     tmp4, tmp1
+        lsl     tmp4, tmp4, #3  /* Bytes beyond alignment -> bits.  */
+
+        mov     tmp2, #~0
+        /* Big-endian.  Early bytes are at MSB.  */
+CPU_BE( lsl     tmp2, tmp2, tmp4 )      /* Shift (tmp1 & 63).  */
+        /* Little-endian.  Early bytes are at LSB.  */
+CPU_LE( lsr     tmp2, tmp2, tmp4 )      /* Shift (tmp1 & 63).  */
+
+        cmp     tmp1, #8
+
+        orr     data1, data1, tmp2
+        orr     data2a, data2, tmp2
+
+        csinv   data1, data1, xzr, le
+        csel    data2, data2, data2a, le
+        b       .Lrealigned
+
+.Lhit_limit:
+        mov     len, limit
+        ret
+ENDPROC(strnlen)