glibc/sysdeps/x86_64/multiarch/strcspn-sse4.c

/* strcspn with SSE4.2 intrinsics
   Copyright (C) 2009-2023 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library 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
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, see
   <https://www.gnu.org/licenses/>.  */

#include <isa-level.h>
#if IS_IN (libc) || MINIMUM_X86_ISA_LEVEL >= 2

# include <nmmintrin.h>
# include <string.h>
# include "varshift.h"

/* We use 0x2:
	_SIDD_SBYTE_OPS
	| _SIDD_CMP_EQUAL_ANY
	| _SIDD_POSITIVE_POLARITY
	| _SIDD_LEAST_SIGNIFICANT
   on pcmpistri to compare xmm/mem128

   0 1 2 3 4 5 6 7 8 9 A B C D E F
   X X X X X X X X X X X X X X X X

   against xmm

   0 1 2 3 4 5 6 7 8 9 A B C D E F
   A A A A A A A A A A A A A A A A

   to find out if the first 16byte data element has any byte A and
   the offset of the first byte.  There are 3 cases:

   1. The first 16byte data element has the byte A at the offset X.
   2. The first 16byte data element has EOS and doesn't have the byte A.
   3. The first 16byte data element is valid and doesn't have the byte A.

   Here is the table of ECX, CFlag, ZFlag and SFlag for 2 cases:

    1		 X	  1	 0/1	  0
    2		16	  0	  1	  0
    3		16	  0	  0	  0

   We exit from the loop for cases 1 and 2 with jbe which branches
   when either CFlag or ZFlag is 1.  If CFlag == 1, ECX has the offset
   X for case 1.  */

# ifndef STRCSPN
#  define STRCSPN __strcspn_sse42
# endif
# ifndef STRCSPN_GENERIC
#  define STRCSPN_GENERIC __strcspn_generic
# endif

# ifdef USE_AS_STRPBRK
#  define RETURN(val1, val2) return val1
# else
#  define RETURN(val1, val2) return val2
# endif

extern
# ifdef USE_AS_STRPBRK
char *
# else
size_t
# endif
STRCSPN_GENERIC (const char *, const char *) attribute_hidden;


# ifdef USE_AS_STRPBRK
char *
# else
size_t
# endif
__attribute__ ((section (".text.sse4.2")))
STRCSPN (const char *s, const char *a)
{
  if (*a == 0)
    RETURN (NULL, strlen (s));

  const char *aligned;
  __m128i mask, maskz, zero;
  unsigned int maskz_bits;
  unsigned int offset = (unsigned int) ((size_t) a & 15);
  zero = _mm_set1_epi8 (0);
  if (offset != 0)
    {
      /* Load masks.  */
      aligned = (const char *) ((size_t) a & -16L);
      __m128i mask0 = _mm_load_si128 ((__m128i *) aligned);
      maskz = _mm_cmpeq_epi8 (mask0, zero);

      /* Find where the NULL terminator is.  */
      maskz_bits = _mm_movemask_epi8 (maskz) >> offset;
      if (maskz_bits != 0)
        {
          mask = __m128i_shift_right (mask0, offset);
          offset = (unsigned int) ((size_t) s & 15);
          if (offset)
            goto start_unaligned;

          aligned = s;
          goto start_loop;
        }
    }

  /* A is aligned.  */
  mask = _mm_loadu_si128 ((__m128i *) a);
  /* Find where the NULL terminator is.  */
  maskz = _mm_cmpeq_epi8 (mask, zero);
  maskz_bits = _mm_movemask_epi8 (maskz);
  if (maskz_bits == 0)
    {
      /* There is no NULL terminator.  Don't use SSE4.2 if the length
         of A > 16.  */
      if (a[16] != 0)
        return STRCSPN_GENERIC (s, a);
    }

  aligned = s;
  offset = (unsigned int) ((size_t) s & 15);
  if (offset != 0)
    {
    start_unaligned:
      /* Check partial string.  */
      aligned = (const char *) ((size_t) s & -16L);
      __m128i value = _mm_load_si128 ((__m128i *) aligned);

      value = __m128i_shift_right (value, offset);

      unsigned int length = _mm_cmpistri (mask, value, 0x2);
      /* No need to check ZFlag since ZFlag is always 1.  */
      unsigned int cflag = _mm_cmpistrc (mask, value, 0x2);
      if (cflag)
	RETURN ((char *) (s + length), length);
      /* Find where the NULL terminator is.  */
      unsigned int index = _mm_cmpistri (value, value, 0x3a);
      if (index < 16 - offset)
	RETURN (NULL, index);
      aligned += 16;
    }

start_loop:
  while (1)
    {
      __m128i value = _mm_load_si128 ((__m128i *) aligned);
      unsigned int index = _mm_cmpistri (mask, value, 0x2);
      unsigned int cflag = _mm_cmpistrc (mask, value, 0x2);
      unsigned int zflag = _mm_cmpistrz (mask, value, 0x2);
      if (cflag)
	RETURN ((char *) (aligned + index), (size_t) (aligned + index - s));
      if (zflag)
	RETURN (NULL,
		/* Find where the NULL terminator is.  */
		(size_t) (aligned + _mm_cmpistri (value, value, 0x3a) - s));
      aligned += 16;
    }
}
#endif