Implement Small String Optimisation (SSO)

Sming/Arch/Host/Components/libc/memrchr.c

@@ -0,0 +1,197 @@
+/* memrchr -- find the last occurrence of a byte in a memory block
+   Copyright (C) 1991-2019 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+   Based on strlen implementation by Torbjorn Granlund ([email protected]),
+   with help from Dan Sahlin ([email protected]) and
+   commentary by Jim Blandy ([email protected]);
+   adaptation to memchr suggested by Dick Karpinski ([email protected]),
+   and implemented by Roland McGrath ([email protected]).
+
+   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 <stdlib.h>
+
+#ifdef HAVE_CONFIG_H
+# include <config.h>
+#endif
+
+#if defined _LIBC
+# include <string.h>
+# include <memcopy.h>
+#endif
+
+#if defined HAVE_LIMITS_H || defined _LIBC
+# include <limits.h>
+#endif
+
+#define LONG_MAX_32_BITS 2147483647
+
+#ifndef LONG_MAX
+# define LONG_MAX LONG_MAX_32_BITS
+#endif
+
+#include <sys/types.h>
+
+#undef __memrchr
+#undef memrchr
+
+#ifndef weak_alias
+# define __memrchr memrchr
+#endif
+
+/* Search no more than N bytes of S for C.  */
+void *
+#ifndef MEMRCHR
+__memrchr
+#else
+MEMRCHR
+#endif
+     (const void *s, int c_in, size_t n)
+{
+  const unsigned char *char_ptr;
+  const unsigned long int *longword_ptr;
+  unsigned long int longword, magic_bits, charmask;
+  unsigned char c;
+
+  c = (unsigned char) c_in;
+
+  /* Handle the last few characters by reading one character at a time.
+     Do this until CHAR_PTR is aligned on a longword boundary.  */
+  for (char_ptr = (const unsigned char *) s + n;
+       n > 0 && ((unsigned long int) char_ptr
+		 & (sizeof (longword) - 1)) != 0;
+       --n)
+    if (*--char_ptr == c)
+      return (void *) char_ptr;
+
+  /* All these elucidatory comments refer to 4-byte longwords,
+     but the theory applies equally well to 8-byte longwords.  */
+
+  longword_ptr = (const unsigned long int *) char_ptr;
+
+  /* Bits 31, 24, 16, and 8 of this number are zero.  Call these bits
+     the "holes."  Note that there is a hole just to the left of
+     each byte, with an extra at the end:
+
+     bits:  01111110 11111110 11111110 11111111
+     bytes: AAAAAAAA BBBBBBBB CCCCCCCC DDDDDDDD
+
+     The 1-bits make sure that carries propagate to the next 0-bit.
+     The 0-bits provide holes for carries to fall into.  */
+  magic_bits = -1;
+  magic_bits = magic_bits / 0xff * 0xfe << 1 >> 1 | 1;
+
+  /* Set up a longword, each of whose bytes is C.  */
+  charmask = c | (c << 8);
+  charmask |= charmask << 16;
+#if LONG_MAX > LONG_MAX_32_BITS
+  charmask |= charmask << 32;
+#endif
+
+  /* Instead of the traditional loop which tests each character,
+     we will test a longword at a time.  The tricky part is testing
+     if *any of the four* bytes in the longword in question are zero.  */
+  while (n >= sizeof (longword))
+    {
+      /* We tentatively exit the loop if adding MAGIC_BITS to
+	 LONGWORD fails to change any of the hole bits of LONGWORD.
+
+	 1) Is this safe?  Will it catch all the zero bytes?
+	 Suppose there is a byte with all zeros.  Any carry bits
+	 propagating from its left will fall into the hole at its
+	 least significant bit and stop.  Since there will be no
+	 carry from its most significant bit, the LSB of the
+	 byte to the left will be unchanged, and the zero will be
+	 detected.
+
+	 2) Is this worthwhile?  Will it ignore everything except
+	 zero bytes?  Suppose every byte of LONGWORD has a bit set
+	 somewhere.  There will be a carry into bit 8.  If bit 8
+	 is set, this will carry into bit 16.  If bit 8 is clear,
+	 one of bits 9-15 must be set, so there will be a carry
+	 into bit 16.  Similarly, there will be a carry into bit
+	 24.  If one of bits 24-30 is set, there will be a carry
+	 into bit 31, so all of the hole bits will be changed.
+
+	 The one misfire occurs when bits 24-30 are clear and bit
+	 31 is set; in this case, the hole at bit 31 is not
+	 changed.  If we had access to the processor carry flag,
+	 we could close this loophole by putting the fourth hole
+	 at bit 32!
+
+	 So it ignores everything except 128's, when they're aligned
+	 properly.
+
+	 3) But wait!  Aren't we looking for C, not zero?
+	 Good point.  So what we do is XOR LONGWORD with a longword,
+	 each of whose bytes is C.  This turns each byte that is C
+	 into a zero.  */
+
+      longword = *--longword_ptr ^ charmask;
+
+      /* Add MAGIC_BITS to LONGWORD.  */
+      if ((((longword + magic_bits)
+
+	    /* Set those bits that were unchanged by the addition.  */
+	    ^ ~longword)
+
+	   /* Look at only the hole bits.  If any of the hole bits
+	      are unchanged, most likely one of the bytes was a
+	      zero.  */
+	   & ~magic_bits) != 0)
+	{
+	  /* Which of the bytes was C?  If none of them were, it was
+	     a misfire; continue the search.  */
+
+	  const unsigned char *cp = (const unsigned char *) longword_ptr;
+
+#if LONG_MAX > 2147483647
+	  if (cp[7] == c)
+	    return (void *) &cp[7];
+	  if (cp[6] == c)
+	    return (void *) &cp[6];
+	  if (cp[5] == c)
+	    return (void *) &cp[5];
+	  if (cp[4] == c)
+	    return (void *) &cp[4];
+#endif
+	  if (cp[3] == c)
+	    return (void *) &cp[3];
+	  if (cp[2] == c)
+	    return (void *) &cp[2];
+	  if (cp[1] == c)
+	    return (void *) &cp[1];
+	  if (cp[0] == c)
+	    return (void *) cp;
+	}
+
+      n -= sizeof (longword);
+    }
+
+  char_ptr = (const unsigned char *) longword_ptr;
+
+  while (n-- > 0)
+    {
+      if (*--char_ptr == c)
+	return (void *) char_ptr;
+    }
+
+  return 0;
+}
+#ifndef MEMRCHR
+# ifdef weak_alias
+weak_alias (__memrchr, memrchr)
+# endif
+#endif

Sming/Core/Data/CStringArray.cpp

@@ -58,9 +58,10 @@ int CStringArray::indexOf(const char* str, bool ignoreCase) const
 		return -1;
 	}
 
+	auto buf = begin();
 	unsigned index = 0;
-	for(unsigned offset = 0; offset < len; ++index) {
-		const char* s = buffer + offset;
+	for(unsigned offset = 0; offset < buflen; ++index) {
+		const char* s = buf + offset;
 		if(ignoreCase) {
 			if(strcasecmp(str, s) == 0) {
 				return index;

Sming/System/include/stringutil.h

@@ -43,6 +43,9 @@ int strcasecmp(const char* s1, const char* s2);
  *  @note non-ANSI GNU C library extension
 */
 void* memmem(const void* haystack, size_t haystacklen, const void* needle, size_t needlelen);
+
+void *memrchr(const void *s, int c, size_t n);
+
 #endif
 
 int memicmp(const void* buf1, const void* buf2, size_t len);