arm64: lib: Implement optimized string compare routines
This patch, based on Linaro's Cortex Strings library, adds
an assembly optimized strcmp() and strncmp() 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>
diff --git a/arch/arm64/lib/strcmp.S b/arch/arm64/lib/strcmp.S
new file mode 100644
index 0000000..42f828b
--- /dev/null
+++ b/arch/arm64/lib/strcmp.S
@@ -0,0 +1,234 @@
+/*
+ * 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>
+
+/*
+ * compare two strings
+ *
+ * Parameters:
+ * x0 - const string 1 pointer
+ * x1 - const string 2 pointer
+ * Returns:
+ * x0 - an integer less than, equal to, or greater than zero
+ * if s1 is found, respectively, to be less than, to match,
+ * or be greater than s2.
+ */
+
+#define REP8_01 0x0101010101010101
+#define REP8_7f 0x7f7f7f7f7f7f7f7f
+#define REP8_80 0x8080808080808080
+
+/* Parameters and result. */
+src1 .req x0
+src2 .req x1
+result .req x0
+
+/* Internal variables. */
+data1 .req x2
+data1w .req w2
+data2 .req x3
+data2w .req w3
+has_nul .req x4
+diff .req x5
+syndrome .req x6
+tmp1 .req x7
+tmp2 .req x8
+tmp3 .req x9
+zeroones .req x10
+pos .req x11
+
+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
+ b .Lcal_cmpresult
+
+.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
+ /* 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 data2, data2, tmp2
+ b .Lstart_realigned
+
+.Lmisaligned8:
+ /*
+ * Get the align offset length to compare per byte first.
+ * After this process, one string's address will be aligned.
+ */
+ and tmp1, src1, #7
+ neg tmp1, tmp1
+ add tmp1, tmp1, #8
+ and tmp2, src2, #7
+ neg tmp2, tmp2
+ add tmp2, tmp2, #8
+ subs tmp3, tmp1, tmp2
+ csel pos, tmp1, tmp2, hi /*Choose the maximum. */
+.Ltinycmp:
+ ldrb data1w, [src1], #1
+ ldrb data2w, [src2], #1
+ subs pos, pos, #1
+ ccmp data1w, #1, #0, ne /* NZCV = 0b0000. */
+ ccmp data1w, data2w, #0, cs /* NZCV = 0b0000. */
+ b.eq .Ltinycmp
+ cbnz pos, 1f /*find the null or unequal...*/
+ cmp data1w, #1
+ ccmp data1w, data2w, #0, cs
+ b.eq .Lstart_align /*the last bytes are equal....*/
+1:
+ sub result, data1, data2
+ ret
+
+.Lstart_align:
+ ands xzr, src1, #7
+ b.eq .Lrecal_offset
+ /*process more leading bytes to make str1 aligned...*/
+ add src1, src1, tmp3
+ add src2, src2, tmp3
+ /*load 8 bytes from aligned str1 and non-aligned str2..*/
+ ldr data1, [src1], #8
+ ldr data2, [src2], #8
+
+ sub tmp1, data1, zeroones
+ orr tmp2, data1, #REP8_7f
+ bic has_nul, tmp1, tmp2
+ eor diff, data1, data2 /* Non-zero if differences found. */
+ orr syndrome, diff, has_nul
+ cbnz syndrome, .Lcal_cmpresult
+ /*How far is the current str2 from the alignment boundary...*/
+ and tmp3, tmp3, #7
+.Lrecal_offset:
+ neg pos, tmp3
+.Lloopcmp_proc:
+ /*
+ * Divide the eight bytes into two parts. First,backwards the src2
+ * to an alignment boundary,load eight bytes from the SRC2 alignment
+ * boundary,then compare with the relative bytes from SRC1.
+ * If all 8 bytes are equal,then start the second part's comparison.
+ * Otherwise finish the comparison.
+ * This special handle can garantee all the accesses are in the
+ * thread/task space in avoid to overrange access.
+ */
+ ldr data1, [src1,pos]
+ ldr data2, [src2,pos]
+ sub tmp1, data1, zeroones
+ orr tmp2, data1, #REP8_7f
+ bic has_nul, tmp1, tmp2
+ eor diff, data1, data2 /* Non-zero if differences found. */
+ orr syndrome, diff, has_nul
+ cbnz syndrome, .Lcal_cmpresult
+
+ /*The second part process*/
+ ldr data1, [src1], #8
+ ldr data2, [src2], #8
+ sub tmp1, data1, zeroones
+ orr tmp2, data1, #REP8_7f
+ bic has_nul, tmp1, tmp2
+ eor diff, data1, data2 /* Non-zero if differences found. */
+ orr syndrome, diff, has_nul
+ cbz syndrome, .Lloopcmp_proc
+
+.Lcal_cmpresult:
+ /*
+ * reversed the byte-order as big-endian,then CLZ can find the most
+ * significant zero bits.
+ */
+CPU_LE( rev syndrome, syndrome )
+CPU_LE( rev data1, data1 )
+CPU_LE( rev data2, data2 )
+
+ /*
+ * 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 ca not just subtract the bytes as the
+ * MSB might be significant.
+ */
+CPU_BE( cbnz has_nul, 1f )
+CPU_BE( cmp data1, data2 )
+CPU_BE( cset result, ne )
+CPU_BE( cneg result, result, lo )
+CPU_BE( ret )
+CPU_BE( 1: )
+ /*Re-compute the NUL-byte detection, using a byte-reversed value. */
+CPU_BE( rev tmp3, data1 )
+CPU_BE( sub tmp1, tmp3, zeroones )
+CPU_BE( orr tmp2, tmp3, #REP8_7f )
+CPU_BE( bic has_nul, tmp1, tmp2 )
+CPU_BE( rev has_nul, has_nul )
+CPU_BE( 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
+ENDPROC(strcmp)