/*-
 * 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 <machine/param.h>

#include "amd64_archlevel.h"

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

ARCHFUNCS(strspn)
        ARCHFUNC(strspn, scalar)
        NOARCHFUNC
        ARCHFUNC(strspn, x86_64_v2)
ENDARCHFUNCS(strspn)

ARCHENTRY(strspn, scalar)
        push    %rbp                    # align stack to enable function call
        mov     %rsp, %rbp
        sub     $256, %rsp              # allocate space for lookup table

        /* check for special cases */
        movzbl  (%rsi), %edx            # first character in the set
        test    %edx, %edx
        jz      .Lzero                  # empty set always returns 0

        movzbl  1(%rsi), %eax           # second character in the set
        test    %eax, %eax
        jz      .Lsingle

        /* no special case matches -- prepare lookup table */
        xor     %r8d, %r8d
        mov     $28, %ecx
0:      mov     %r8, (%rsp, %rcx, 8)
        mov     %r8, 8(%rsp, %rcx, 8)
        mov     %r8, 16(%rsp, %rcx, 8)
        mov     %r8, 24(%rsp, %rcx, 8)
        sub     $4, %ecx
        jnc     0b

        movb    $1, (%rsp, %rdx, 1)     # register first char in set
        add     $2, %rsi

        /* process remaining chars in set */
        ALIGN_TEXT
0:      movb    $1, (%rsp, %rax, 1)     # register previous char
        movzbl  (%rsi), %eax            # next char in set
        test    %eax, %eax              # end of string?
        jz      1f

        movb    $1, (%rsp, %rax, 1)
        add     $2, %rsi
        movzbl  -1(%rsi), %eax
        test    %eax, %eax
        jnz     0b

1:      mov     %rdi, %rax              # a copy of the source to iterate over

        /* find mismatch */
        ALIGN_TEXT
0:      movzbl  (%rax), %ecx
        cmpb    $0, (%rsp, %rcx, 1)
        je      2f

        movzbl  1(%rax), %ecx
        cmpb    $0, (%rsp, %rcx, 1)
        je      3f

        movzbl  2(%rax), %ecx
        cmpb    $0, (%rsp, %rcx, 1)
        je      4f

        movzbl  3(%rax), %ecx
        add     $4, %rax
        cmpb    $0, (%rsp, %rcx, 1)
        jne     0b

        sub     $3, %rax
4:      dec     %rdi
3:      inc     %rax
2:      sub     %rdi, %rax              # number of characters preceding match
        leave
        ret

        /* empty set never matches */
.Lzero: xor     %eax, %eax
        leave
        ret

        /* find repeated single character */
        ALIGN_TEXT
.Lsingle:
        cmpb    %dl, (%rdi, %rax, 1)
        jne     1f

        cmpb    %dl, 1(%rdi, %rax, 1)
        jne     2f

        cmpb    %dl, 2(%rdi, %rax, 1)
        jne     3f

        cmpb    %dl, 3(%rdi, %rax, 1)
        lea     4(%rax), %rax
        je      .Lsingle

        sub     $3, %rax
3:      inc     %rax
2:      inc     %rax
1:      leave
        ret
ARCHEND(strspn, scalar)

        /*
         * This kernel uses pcmpistri to do the heavy lifting.
         * We provide three code paths, depending on set size:
         *
         *  0--16: one pcmpistri per 16 bytes of input
         * 17--32: two pcmpistri per 16 bytes of input
         *   >=33: fall back to look up table
         */
ARCHENTRY(strspn, x86_64_v2)
        push            %rbp
        mov             %rsp, %rbp
        sub             $256, %rsp

        /* find set size and copy up to 32 bytes to (%rsp) */
        mov             %esi, %ecx
        and             $~0xf, %rsi             # align set pointer
        movdqa          (%rsi), %xmm0
        pxor            %xmm1, %xmm1
        and             $0xf, %ecx              # amount of bytes rsi is past alignment
        xor             %edx, %edx
        pcmpeqb         %xmm0, %xmm1            # end of string reached?
        movdqa          %xmm0, 32(%rsp)         # transfer head of set to stack
        pmovmskb        %xmm1, %eax
        shr             %cl, %eax               # clear out junk before string
        test            %eax, %eax              # end of set reached?
        jnz             0f

        movdqa          16(%rsi), %xmm0         # second chunk of the set
        mov             $16, %edx
        sub             %ecx, %edx              # length of set preceding xmm0
        pxor            %xmm1, %xmm1
        pcmpeqb         %xmm0, %xmm1
        movdqa          %xmm0, 48(%rsp)
        movdqu          32(%rsp, %rcx, 1), %xmm2 # head of set
        pmovmskb        %xmm1, %eax
        test            %eax, %eax
        jnz             1f

        movdqa          32(%rsi), %xmm0         # third chunk
        add             $16, %edx
        pxor            %xmm1, %xmm1
        pcmpeqb         %xmm0, %xmm1
        movdqa          %xmm0, 64(%rsp)
        pmovmskb        %xmm1, %eax
        test            %eax, %eax              # still not done?
        jz              .Lgt32v2

0:      movdqu          32(%rsp, %rcx, 1), %xmm2 # head of set
1:      tzcnt           %eax, %eax
        add             %eax, %edx              # length of set (excluding NUL byte)
        cmp             $32, %edx               # above 32 bytes?
        ja              .Lgt32v2

        /*
         * At this point we know that we want to use pcmpistri.
         * one last problem obtains: the head of the string is not
         * aligned and may cross a cacheline.  If this is the case,
         * we take the part before the page boundary and repeat the
         * last byte to fill up the xmm register.
         */
        mov             %rdi, %rax              # save original string pointer
        lea             15(%rdi), %esi          # last byte of the head
        xor             %edi, %esi
        test            $PAGE_SIZE, %esi        # does the head cross a page?
        jz              0f

        /* head crosses page: copy to stack to fix up */
        and             $~0xf, %rax             # align head pointer temporarily
        movzbl          15(%rax), %esi          # last head byte on the page
        movdqa          (%rax), %xmm0
        movabs          $0x0101010101010101, %r8
        imul            %r8, %rsi               # repeated 8 times
        movdqa          %xmm0, (%rsp)           # head word on stack
        mov             %rsi, 16(%rsp)          # followed by filler (last byte x8)
        mov             %rsi, 24(%rsp)
        mov             %edi, %eax
        and             $0xf, %eax              # offset of head from alignment
        add             %rsp, %rax              # pointer to fake head

0:      movdqu          (%rax), %xmm1           # load head (fake or real)
        lea             16(%rdi), %rax
        and             $~0xf, %rax             # second 16 bytes of string (aligned)
1:      cmp             $16, %edx               # 16--32 bytes?
        ja              .Lgt16v2


        /* set is 2--16 bytes in size */

        /* _SIDD_UBYTE_OPS|_SIDD_CMP_EQUAL_ANY|_SIDD_LEAST_SIGNIFICANT|_SIDD_NEGATIVE_POLARITY */
        pcmpistri       $0x10, %xmm1, %xmm2     # match in head?
        jc              .Lheadmismatchv2

        ALIGN_TEXT
0:      pcmpistri       $0x10, (%rax), %xmm2
        jc              1f                      # match or end of string?
        pcmpistri       $0x10, 16(%rax), %xmm2
        lea             32(%rax), %rax
        jnc             0b                      # match or end of string?

        sub             $16, %rax               # go back to second half
1:      sub             %rdi, %rax              # offset of (%rax) from beginning of string
        add             %rcx, %rax              # prefix length before match/NUL
        leave
        ret

.Lheadmismatchv2:
        mov             %ecx, %eax              # prefix length before mismatch/NUL
        leave
        ret

        /* set is 17--32 bytes in size */
.Lgt16v2:
        movdqu          48(%rsp, %rcx, 1), %xmm3 # second part of set

        /* _SIDD_UBYTE_OPS|_SIDD_CMP_EQUAL_ANY|_SIDD_BIT_MASK|_SIDD_NEGATIVE_POLARITY */
        pcmpistrm       $0x10, %xmm1, %xmm2     # any mismatch in first half?
        movdqa          %xmm0, %xmm4
        pcmpistrm       $0x10, %xmm1, %xmm3     # any mismatch in the second half?
        ptest           %xmm0, %xmm4            # any entry that doesn't match either?
        jnz             2f

        ALIGN_TEXT
0:      movdqa          (%rax), %xmm1
        pcmpistrm       $0x10, %xmm1, %xmm2
        movdqa          %xmm0, %xmm4
        pcmpistrm       $0x10, %xmm1, %xmm3
        ptest           %xmm0, %xmm4
        jnz             1f
        movdqa          16(%rax), %xmm1
        add             $32, %rax
        pcmpistrm       $0x10, %xmm1, %xmm2
        movdqa          %xmm0, %xmm4
        pcmpistrm       $0x10, %xmm1, %xmm3
        ptest           %xmm0, %xmm4
        jz              0b

        sub             $16, %rax
1:      pand            %xmm4, %xmm0
        movd            %xmm0, %ecx
        sub             %rdi, %rax              # offset of %xmm1 from beginning of string
        tzcnt           %ecx, %ecx
        add             %rcx, %rax              # prefix length before match/NUL
        leave
        ret

        /* mismatch or string end in head */
2:      pand            %xmm4, %xmm0            # bit mask of mismatches (end of string counts)
        movd            %xmm0, %eax
        tzcnt           %eax, %eax              # prefix length before mismatch/NUL
        leave
        ret

        /* set is >=33 bytes in size */
.Lgt32v2:
        xorps   %xmm0, %xmm0
        mov     $256-64, %edx

        /* clear out look up table */
0:      movaps  %xmm0, (%rsp, %rdx, 1)
        movaps  %xmm0, 16(%rsp, %rdx, 1)
        movaps  %xmm0, 32(%rsp, %rdx, 1)
        movaps  %xmm0, 48(%rsp, %rdx, 1)
        sub     $64, %edx
        jnc     0b

        add     %rcx, %rsi              # restore string pointer
        mov     %rdi, %rax              # keep a copy of the string

        /* initialise look up table */
        movzbl  (%rsi), %ecx            # string is known not to be empty

        ALIGN_TEXT
0:      movb    $1, (%rsp, %rcx, 1)
        movzbl  1(%rsi), %ecx
        test    %ecx, %ecx
        jz      1f

        movb    $1, (%rsp, %rcx, 1)
        movzbl  2(%rsi), %ecx
        test    %ecx, %ecx
        jz      1f

        movb    $1, (%rsp, %rcx, 1)
        movzbl  3(%rsi), %ecx
        add     $4, %rsi
        test    %ecx, %ecx
        jz      1f

        movb    $1, (%rsp, %rcx, 1)
        movzbl  (%rsi), %ecx
        test    %ecx, %ecx
        jnz     0b

        /* find match */
        ALIGN_TEXT
1:      movzbl  (%rax), %ecx
        cmpb    $0, (%rsp, %rcx, 1)
        je      2f

        movzbl  1(%rax), %ecx
        cmpb    $0, (%rsp, %rcx, 1)
        je      3f

        movzbl  2(%rax), %ecx
        cmpb    $0, (%rsp, %rcx, 1)
        je      4f

        movzbl  3(%rax), %ecx
        add     $4, %rax
        cmpb    $0, (%rsp, %rcx, 1)
        jne     1b

        sub     $3, %rax
4:      dec     %rdi
3:      inc     %rax
2:      sub     %rdi, %rax              # number of characters preceding match
        leave
        ret
ARCHEND(strspn, x86_64_v2)

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