/*-
 * Copyright (c) 2023 The FreeBSD Foundation
 *
 * This software was developed by Robert Clausecker <fuz@FreeBSD.org>
 * under sponsorship from the FreeBSD Foundation.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. 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.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR 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 AUTHOR 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
 */

#include <machine/asm.h>

#include "amd64_archlevel.h"

#define ALIGN_TEXT      .p2align 4,0x90 # 16-byte alignment, nop-filled

        .weak   strchrnul
        .set    strchrnul, __strchrnul

ARCHFUNCS(__strchrnul)
        ARCHFUNC(__strchrnul, scalar)
        ARCHFUNC(__strchrnul, baseline)
ENDARCHFUNCS(__strchrnul)

/*
 * strchrnul(str, c)
 * This is implemented like strlen(str), but we check for the
 * presence of both NUL and c in each iteration.
 */
ARCHENTRY(__strchrnul, scalar)
        mov     %edi, %ecx
        and     $~7, %rdi               # align to 8 byte
        movzbl  %sil, %esi              # clear stray high bits
        movabs  $0x0101010101010101, %r8
        mov     (%rdi), %rax            # load first word
        imul    %r8, %rsi               # replicate char 8 times

        /*
         * Unaligned input: align to 8 bytes.  Then proceed the same
         * way as with aligned input, but prevent matches before the
         * beginning of the string.  This is achieved by oring 0x01
         * into each byte of the buffer before the string
         */
        shl     $3, %ecx
        mov     %r8, %r10
        add     $8, %rdi
        shl     %cl, %r10               # 0x01 where the string is
        xor     %r8, %r10               # 0x01 where it is not
        neg     %r8                     # negate 01..01 so we can use lea
        movabs  $0x8080808080808080, %r9

        mov     %rsi, %rcx
        xor     %rax, %rcx              # str ^ c
        or      %r10, %rax              # str without NUL bytes before it
        or      %r10, %rcx              # (str ^ c) without matches before it
        lea     (%rax, %r8, 1), %rdx    # str - 0x01..01
        lea     (%rcx, %r8, 1), %r11    # (str ^ c) - 0x01..01
        not     %rax                    # ~str
        not     %rcx                    # ~(str ^ c)
        and     %rdx, %rax              # (str - 0x01..01) & ~str
        and     %r11, %rcx              # ((str ^ c - 0x01..01) & ~(str ^ c)
        or      %rcx, %rax              # matches for both
        and     %r9, %rax               # not including junk bytes
        jnz     1f

        /* main loop unrolled twice */
        ALIGN_TEXT
0:      mov     (%rdi), %rax            # str
        mov     %rsi, %rcx
        xor     %rax, %rcx              # str ^ c
        lea     (%rax, %r8, 1), %rdx    # str - 0x01..01
        lea     (%rcx, %r8, 1), %r11    # (str ^ c) - 0x01..01
        not     %rax                    # ~str
        not     %rcx                    # ~(str ^ c)
        and     %rdx, %rax              # (str - 0x01..01) & ~str
        and     %r11, %rcx              # ((str ^ c - 0x01..01) & ~(str ^ c)
        or      %rcx, %rax              # matches for both
        and     %r9, %rax               # not including junk bits
        jnz     2f

        mov     8(%rdi), %rax           # str
        add     $16, %rdi
        mov     %rsi, %rcx
        xor     %rax, %rcx              # str ^ c
        lea     (%rax, %r8, 1), %rdx    # str - 0x01..01
        lea     (%rcx, %r8, 1), %r11    # (str ^ c) - 0x01..01
        not     %rax                    # ~str
        not     %rcx                    # ~(str ^ c)
        and     %rdx, %rax              # (str - 0x01..01) & ~str
        and     %r11, %rcx              # ((str ^ c - 0x01..01) & ~(str ^ c)
        or      %rcx, %rax              # matches for both
        and     %r9, %rax               # not including junk bits
        jz      0b

        /* NUL or c found */
1:      sub     $8, %rdi                # undo advance past buffer
2:      tzcnt   %rax, %rax              # first NUL or c byte match
        shr     $3, %eax                # scale from bit to byte index
        add     %rdi, %rax              # pointer to found c or NUL
        ret
ARCHEND(__strchrnul, scalar)

ARCHENTRY(__strchrnul, baseline)
        mov             %edi, %ecx
        and             $~0xf, %rdi             # align to 16 byte
        movdqa          (%rdi), %xmm1
        movd            %esi, %xmm0
        and             $0xf, %ecx              # distance from (%rdi) to start of string
        pxor            %xmm2, %xmm2
        mov             $-1, %edx
        punpcklbw       %xmm0, %xmm0            # c -> cc
        shl             %cl, %edx               # bits corresponding to bytes in the string
        punpcklwd       %xmm0, %xmm0            # cc -> cccc
        add             $16, %rdi

        /* check for match in head */
        pcmpeqb         %xmm1, %xmm2            # NUL bytes present?
        pshufd          $0, %xmm0, %xmm0        # cccc -> cccccccccccccccc
        pcmpeqb         %xmm0, %xmm1            # c present?
        por             %xmm2, %xmm1            # either present?
        pmovmskb        %xmm1, %eax
        and             %edx, %eax              # match in the string?
        jnz             1f

        /* main loop unrolled twice */
        ALIGN_TEXT
0:      movdqa          (%rdi), %xmm1
        pxor            %xmm2, %xmm2
        pcmpeqb         %xmm1, %xmm2            # NUL bytes present?
        pcmpeqb         %xmm0, %xmm1            # c present?
        por             %xmm2, %xmm1            # either present?
        pmovmskb        %xmm1, %eax
        test            %eax, %eax              # match in the string?
        jnz             2f

        movdqa          16(%rdi), %xmm1
        add             $32, %rdi
        pxor            %xmm2, %xmm2
        pcmpeqb         %xmm1, %xmm2            # NUL bytes present?
        pcmpeqb         %xmm0, %xmm1            # c present?
        por             %xmm2, %xmm1            # either present?
        pmovmskb        %xmm1, %eax
        test            %eax, %eax              # match in the string?
        jz              0b

1:      sub             $16, %rdi               # undo advance past buffer
2:      tzcnt           %eax, %eax              # where is the match?
        add             %rdi, %rax              # pointer to found c or NUL
        ret
ARCHEND(__strchrnul, baseline)

        .section .note.GNU-stack,"",%progbits