1 files changed, 201 insertions, 0 deletions

diff --git a/gl/memchr.c b/gl/memchr.c
new file mode 100644
index 0000000..d44ad6d
--- /dev/null
+++ b/gl/memchr.c
@@ -0,0 +1,201 @@
+/* Copyright (C) 1991, 1993, 1996, 1997, 1999, 2000, 2003, 2004, 2006 Free
+   Software Foundation, Inc.
+
+   Based on strlen implementation by Torbjorn Granlund (tege@sics.se),
+   with help from Dan Sahlin (dan@sics.se) and
+   commentary by Jim Blandy (jimb@ai.mit.edu);
+   adaptation to memchr suggested by Dick Karpinski (dick@cca.ucsf.edu),
+   and implemented by Roland McGrath (roland@ai.mit.edu).
+
+NOTE: The canonical source of this file is maintained with the GNU C Library.
+Bugs can be reported to bug-glibc@prep.ai.mit.edu.
+
+This program is free software; you can redistribute it and/or modify it
+under the terms of the GNU General Public License as published by the
+Free Software Foundation; either version 2, or (at your option) any
+later version.
+
+This program 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 General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program; if not, write to the Free Software Foundation,
+Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */
+
+#ifndef _LIBC
+# include <config.h>
+#endif
+
+#include <string.h>
+
+#include <stddef.h>
+
+#if defined _LIBC
+# include <memcopy.h>
+#else
+# define reg_char char
+#endif
+
+#include <limits.h>
+
+#if HAVE_BP_SYM_H || defined _LIBC
+# include <bp-sym.h>
+#else
+# define BP_SYM(sym) sym
+#endif
+
+#undef memchr
+#undef __memchr
+
+/* Search no more than N bytes of S for C.  */
+void *
+__memchr (void const *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 reg_char c;
+  int i;
+
+  c = (unsigned char) c_in;
+
+  /* Handle the first 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 > 0 && (size_t) char_ptr % sizeof longword != 0;
+       --n, ++char_ptr)
+    if (*char_ptr == c)
+      return (void *) char_ptr;
+
+  /* All these elucidatory comments refer to 4-byte longwords,
+     but the theory applies equally well to any size 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.  */
+
+  /* Set MAGIC_BITS to be this pattern of 1 and 0 bits.
+     Set CHARMASK to be a longword, each of whose bytes is C.  */
+
+  magic_bits = 0xfefefefe;
+  charmask = c | (c << 8);
+  charmask |= charmask << 16;
+#if 0xffffffffU < ULONG_MAX
+  magic_bits |= magic_bits << 32;
+  charmask |= charmask << 32;
+  if (8 < sizeof longword)
+    for (i = 64; i < sizeof longword * 8; i *= 2)
+      {
+        magic_bits |= magic_bits << i;
+        charmask |= charmask << i;
+      }
+#endif
+  magic_bits = (ULONG_MAX >> 1) & (magic_bits | 1);
+
+  /* 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 - 1);
+
+          if (cp[0] == c)
+            return (void *) cp;
+          if (cp[1] == c)
+            return (void *) &cp[1];
+          if (cp[2] == c)
+            return (void *) &cp[2];
+          if (cp[3] == c)
+            return (void *) &cp[3];
+          if (4 < sizeof longword && cp[4] == c)
+            return (void *) &cp[4];
+          if (5 < sizeof longword && cp[5] == c)
+            return (void *) &cp[5];
+          if (6 < sizeof longword && cp[6] == c)
+            return (void *) &cp[6];
+          if (7 < sizeof longword && cp[7] == c)
+            return (void *) &cp[7];
+          if (8 < sizeof longword)
+            for (i = 8; i < sizeof longword; i++)
+              if (cp[i] == c)
+                return (void *) &cp[i];
+        }
+
+      n -= sizeof longword;
+    }
+
+  char_ptr = (const unsigned char *) longword_ptr;
+
+  while (n-- > 0)
+    {
+      if (*char_ptr == c)
+        return (void *) char_ptr;
+      else
+        ++char_ptr;
+    }
+
+  return 0;
+}
+#ifdef weak_alias
+weak_alias (__memchr, BP_SYM (memchr))
+#endif