diff options
Diffstat (limited to 'libc/arch-arm64/default/bionic/strcmp.S')
| -rw-r--r-- | libc/arch-arm64/default/bionic/strcmp.S | 192 |
1 files changed, 192 insertions, 0 deletions
diff --git a/libc/arch-arm64/default/bionic/strcmp.S b/libc/arch-arm64/default/bionic/strcmp.S new file mode 100644 index 000000000..dfac7c42c --- /dev/null +++ b/libc/arch-arm64/default/bionic/strcmp.S @@ -0,0 +1,192 @@ +/* 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 L(label) .L ## label + +#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_default) +.p2align 6 + eor tmp1, src1, src2 + mov zeroones, #REP8_01 + tst tmp1, #7 + b.ne L(misaligned8) + ands tmp1, src1, #7 + b.ne L(mutual_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. */ +L(loop_aligned): + ldr data1, [src1], #8 + ldr data2, [src2], #8 +L(start_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, L(loop_aligned) + /* End of performance-critical section -- one 64B cache line. */ + +L(end): +#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 + +L(mutual_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 L(start_realigned) + +L(misaligned8): + /* Align SRC1 to 8 bytes and then compare 8 bytes at a time, always + checking to make sure that we don't access beyond page boundary in + SRC2. */ + tst src1, #7 + b.eq L(loop_misaligned) +L(do_misaligned): + ldrb data1w, [src1], #1 + ldrb data2w, [src2], #1 + cmp data1w, #1 + ccmp data1w, data2w, #0, cs /* NZCV = 0b0000. */ + b.ne L(done) + tst src1, #7 + b.ne L(do_misaligned) + +L(loop_misaligned): + /* Test if we are within the last dword of the end of a 4K page. If + yes then jump back to the misaligned loop to copy a byte at a time. */ + and tmp1, src2, #0xff8 + eor tmp1, tmp1, #0xff8 + cbz tmp1, L(do_misaligned) + ldr data1, [src1], #8 + ldr data2, [src2], #8 + + 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, L(loop_misaligned) + b L(end) + +L(done): + sub result, data1, data2 + ret +END(strcmp_default) |