source: trunk/libs/newlib/src/newlib/libc/machine/aarch64/strchrnul.S @ 444

/*
   strchrnul - find a character or nul in a string

   Copyright (c) 2014, ARM 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 company 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.  */

#if (defined (__OPTIMIZE_SIZE__) || defined (PREFER_SIZE_OVER_SPEED))
/* See strchrnul-stub.c  */
#else

/* Assumptions:
 *
 * ARMv8-a, AArch64
 * Neon Available.
 */

/* Arguments and results.  */
#define srcin           x0
#define chrin           w1

#define result          x0

#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        v7
#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.  */

/* Locals and temporaries.  */

        .macro def_fn f p2align=0
        .text
        .p2align \p2align
        .global \f
        .type \f, %function
\f:
        .endm

def_fn 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    .Lloop

        /* 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, .Ltail

.Lloop:
        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, .Lloop

        /* 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]
.Ltail:
        /* 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

        .size   strchrnul, . - strchrnul
#endif