[Qemu-devel] [RFC v5 1/2] util: add memmem replacement function

[hw . claudio]

From: Claudio Fontana <address@hidden>

if the memmem function is missing, provide the gnulib replacement.

Signed-off-by: Claudio Fontana <address@hidden>
---
 configure            |  15 ++
 include/qemu/osdep.h |   4 +
 util/Makefile.objs   |   1 +
 util/memmem.c        |  73 +++++++++
 util/str-two-way.h   | 452 +++++++++++++++++++++++++++++++++++++++++++++++++++
 5 files changed, 545 insertions(+)
 create mode 100644 util/memmem.c
 create mode 100644 util/str-two-way.h

diff --git a/configure b/configure
index 1f0f485..feb55b1 100755
--- a/configure
+++ b/configure
@@ -3078,6 +3078,17 @@ if compile_prog "" "" ; then
 fi
 
 ##########################################
+# memmem probe
+cat > $TMPC <<EOF
+#include <string.h>
+int main(int argc, char *argv[]) { return memmem(argv[0], 0, argv[0], 0) != 
argv[0]; }
+EOF
+memmem=no
+if compile_prog "" "" ; then
+  memmem=yes
+fi
+
+##########################################
 # fdt probe
 # fdt support is mandatory for at least some target architectures,
 # so insist on it if we're building those system emulators.
@@ -4431,6 +4442,7 @@ echo "RDMA support      $rdma"
 echo "TCG interpreter   $tcg_interpreter"
 echo "fdt support       $fdt"
 echo "preadv support    $preadv"
+echo "memmem support    $memmem"
 echo "fdatasync         $fdatasync"
 echo "madvise           $madvise"
 echo "posix_madvise     $posix_madvise"
@@ -4780,6 +4792,9 @@ fi
 if test "$preadv" = "yes" ; then
   echo "CONFIG_PREADV=y" >> $config_host_mak
 fi
+if test "$memmem" = "yes" ; then
+  echo "CONFIG_MEMMEM=y" >> $config_host_mak
+fi
 if test "$fdt" = "yes" ; then
   echo "CONFIG_FDT=y" >> $config_host_mak
 fi
diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h
index b3300cc..d74ddff 100644
--- a/include/qemu/osdep.h
+++ b/include/qemu/osdep.h
@@ -201,6 +201,10 @@ ssize_t writev(int fd, const struct iovec *iov, int 
iov_cnt);
 #include <sys/uio.h>
 #endif
 
+#ifndef CONFIG_MEMMEM
+void *memmem(const void *hay, size_t hay_len, const void *s, size_t s_len);
+#endif /* !CONFIG_MEMMEM */
+
 #ifdef _WIN32
 static inline void qemu_timersub(const struct timeval *val1,
                                  const struct timeval *val2,
diff --git a/util/Makefile.objs b/util/Makefile.objs
index ceaba30..628242f 100644
--- a/util/Makefile.objs
+++ b/util/Makefile.objs
@@ -1,6 +1,7 @@
 util-obj-y = osdep.o cutils.o unicode.o qemu-timer-common.o
 util-obj-$(CONFIG_WIN32) += oslib-win32.o qemu-thread-win32.o 
event_notifier-win32.o
 util-obj-$(CONFIG_POSIX) += oslib-posix.o qemu-thread-posix.o 
event_notifier-posix.o qemu-openpty.o
+util-obj-$(call lnot,$(CONFIG_MEMMEM)) += memmem.o
 util-obj-y += envlist.o path.o module.o
 util-obj-$(call lnot,$(CONFIG_INT128)) += host-utils.o
 util-obj-y += bitmap.o bitops.o hbitmap.o
diff --git a/util/memmem.c b/util/memmem.c
new file mode 100644
index 0000000..951d0ec
--- /dev/null
+++ b/util/memmem.c
@@ -0,0 +1,73 @@
+/* Copyright (C) 1991-1994, 1996-1998, 2000, 2004, 2007-2015 Free Software
+   Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   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, see <http://www.gnu.org/licenses/>.  */
+
+/* This particular implementation was written by Eric Blake, 2008.  */
+
+/* QEMU notes:
+ * slighly modified for integration into QEMU, Claudio Fontana, 2015:
+ *  - use qemu-common.h
+ *  - removed check for CHAR_BIT for setting LONG_NEEDLE_THRESHOLD.
+ */
+
+#include <qemu-common.h>
+
+#define RETURN_TYPE void *
+#define AVAILABLE(h, h_l, j, n_l) ((j) <= (h_l) - (n_l))
+#define LONG_NEEDLE_THRESHOLD 32U
+#include "str-two-way.h"
+
+/* Return the first occurrence of NEEDLE in HAYSTACK.  Return HAYSTACK
+   if NEEDLE_LEN is 0, otherwise NULL if NEEDLE is not found in
+   HAYSTACK.  */
+void *
+memmem (const void *haystack_start, size_t haystack_len,
+        const void *needle_start, size_t needle_len)
+{
+  /* Abstract memory is considered to be an array of 'unsigned char' values,
+     not an array of 'char' values.  See ISO C 99 section 6.2.6.1.  */
+  const unsigned char *haystack = (const unsigned char *) haystack_start;
+  const unsigned char *needle = (const unsigned char *) needle_start;
+
+  if (needle_len == 0)
+    /* The first occurrence of the empty string is deemed to occur at
+       the beginning of the string.  */
+    return (void *) haystack;
+
+  /* Sanity check, otherwise the loop might search through the whole
+     memory.  */
+  if (__builtin_expect (haystack_len < needle_len, 0))
+    return NULL;
+
+  /* Use optimizations in memchr when possible, to reduce the search
+     size of haystack using a linear algorithm with a smaller
+     coefficient.  However, avoid memchr for long needles, since we
+     can often achieve sublinear performance.  */
+  if (needle_len < LONG_NEEDLE_THRESHOLD)
+    {
+      haystack = memchr (haystack, *needle, haystack_len);
+      if (!haystack || __builtin_expect (needle_len == 1, 0))
+        return (void *) haystack;
+      haystack_len -= haystack - (const unsigned char *) haystack_start;
+      if (haystack_len < needle_len)
+        return NULL;
+      return two_way_short_needle (haystack, haystack_len, needle, needle_len);
+    }
+  else
+    return two_way_long_needle (haystack, haystack_len, needle, needle_len);
+}
+
+#undef LONG_NEEDLE_THRESHOLD
diff --git a/util/str-two-way.h b/util/str-two-way.h
new file mode 100644
index 0000000..d8741dd
--- /dev/null
+++ b/util/str-two-way.h
@@ -0,0 +1,452 @@
+/* Byte-wise substring search, using the Two-Way algorithm.
+   Copyright (C) 2008-2015 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+   Written by Eric Blake <address@hidden>, 2008.
+
+   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, see <http://www.gnu.org/licenses/>.  */
+
+/* QEMU notes:
+ * slighly modified for integration into QEMU, Claudio Fontana, 2015:
+ *  - removed check for CHAR_BIT for setting LONG_NEEDLE_THRESHOLD.
+ *  - adjust comments accordingly.
+ */
+
+/* Before including this file, you need to include qemu-common.h and define:
+     RESULT_TYPE             A macro that expands to the return type.
+     AVAILABLE(h, h_l, j, n_l)
+                             A macro that returns nonzero if there are
+                             at least N_L bytes left starting at H[J].
+                             H is 'unsigned char *', H_L, J, and N_L
+                             are 'size_t'; H_L is an lvalue.  For
+                             NUL-terminated searches, H_L can be
+                             modified each iteration to avoid having
+                             to compute the end of H up front.
+
+  For case-insensitivity, you may optionally define:
+     CMP_FUNC(p1, p2, l)     A macro that returns 0 iff the first L
+                             characters of P1 and P2 are equal.
+     CANON_ELEMENT(c)        A macro that canonicalizes an element right after
+                             it has been fetched from one of the two strings.
+                             The argument is an 'unsigned char'; the result
+                             must be an 'unsigned char' as well.
+     LONG_NEEDLE_THRESHOLD   Point at which computing a bad-byte shift table
+                             is likely to be worthwhile (default is 32 bytes).
+*/
+
+#include <limits.h>
+#include <stdint.h>
+
+/* We use the Two-Way string matching algorithm (also known as
+   Chrochemore-Perrin), which guarantees linear complexity with
+   constant space.  Additionally, for long needles, we also use a bad
+   character shift table similar to the Boyer-Moore algorithm to
+   achieve improved (potentially sub-linear) performance.
+
+   See http://www-igm.univ-mlv.fr/~lecroq/string/node26.html#SECTION00260,
+   http://en.wikipedia.org/wiki/Boyer-Moore_string_search_algorithm,
+   
http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.34.6641&rep=rep1&type=pdf
+*/
+
+/* Point at which computing a bad-byte shift table is likely to be
+   worthwhile.  Small needles should not compute a table, since it
+   adds (1 << CHAR_BIT) + NEEDLE_LEN computations of preparation for a
+   speedup no greater than a factor of NEEDLE_LEN.  The larger the
+   needle, the better the potential performance gain. */
+#ifndef LONG_NEEDLE_THRESHOLD
+# define LONG_NEEDLE_THRESHOLD 32U
+#endif
+
+#ifndef MAX
+# define MAX(a, b) ((a < b) ? (b) : (a))
+#endif
+
+#ifndef CANON_ELEMENT
+# define CANON_ELEMENT(c) c
+#endif
+#ifndef CMP_FUNC
+# define CMP_FUNC memcmp
+#endif
+
+/* Perform a critical factorization of NEEDLE, of length NEEDLE_LEN.
+   Return the index of the first byte in the right half, and set
+   *PERIOD to the global period of the right half.
+
+   The global period of a string is the smallest index (possibly its
+   length) at which all remaining bytes in the string are repetitions
+   of the prefix (the last repetition may be a subset of the prefix).
+
+   When NEEDLE is factored into two halves, a local period is the
+   length of the smallest word that shares a suffix with the left half
+   and shares a prefix with the right half.  All factorizations of a
+   non-empty NEEDLE have a local period of at least 1 and no greater
+   than NEEDLE_LEN.
+
+   A critical factorization has the property that the local period
+   equals the global period.  All strings have at least one critical
+   factorization with the left half smaller than the global period.
+   And while some strings have more than one critical factorization,
+   it is provable that with an ordered alphabet, at least one of the
+   critical factorizations corresponds to a maximal suffix.
+
+   Given an ordered alphabet, a critical factorization can be computed
+   in linear time, with 2 * NEEDLE_LEN comparisons, by computing the
+   shorter of two ordered maximal suffixes.  The ordered maximal
+   suffixes are determined by lexicographic comparison while tracking
+   periodicity.  */
+static size_t
+critical_factorization (const unsigned char *needle, size_t needle_len,
+                        size_t *period)
+{
+  /* Index of last byte of left half, or SIZE_MAX.  */
+  size_t max_suffix, max_suffix_rev;
+  size_t j; /* Index into NEEDLE for current candidate suffix.  */
+  size_t k; /* Offset into current period.  */
+  size_t p; /* Intermediate period.  */
+  unsigned char a, b; /* Current comparison bytes.  */
+
+  /* Special case NEEDLE_LEN of 1 or 2 (all callers already filtered
+     out 0-length needles.  */
+  if (needle_len < 3)
+    {
+      *period = 1;
+      return needle_len - 1;
+    }
+
+  /* Invariants:
+     0 <= j < NEEDLE_LEN - 1
+     -1 <= max_suffix{,_rev} < j (treating SIZE_MAX as if it were signed)
+     min(max_suffix, max_suffix_rev) < global period of NEEDLE
+     1 <= p <= global period of NEEDLE
+     p == global period of the substring NEEDLE[max_suffix{,_rev}+1...j]
+     1 <= k <= p
+  */
+
+  /* Perform lexicographic search.  */
+  max_suffix = SIZE_MAX;
+  j = 0;
+  k = p = 1;
+  while (j + k < needle_len)
+    {
+      a = CANON_ELEMENT (needle[j + k]);
+      b = CANON_ELEMENT (needle[max_suffix + k]);
+      if (a < b)
+        {
+          /* Suffix is smaller, period is entire prefix so far.  */
+          j += k;
+          k = 1;
+          p = j - max_suffix;
+        }
+      else if (a == b)
+        {
+          /* Advance through repetition of the current period.  */
+          if (k != p)
+            ++k;
+          else
+            {
+              j += p;
+              k = 1;
+            }
+        }
+      else /* b < a */
+        {
+          /* Suffix is larger, start over from current location.  */
+          max_suffix = j++;
+          k = p = 1;
+        }
+    }
+  *period = p;
+
+  /* Perform reverse lexicographic search.  */
+  max_suffix_rev = SIZE_MAX;
+  j = 0;
+  k = p = 1;
+  while (j + k < needle_len)
+    {
+      a = CANON_ELEMENT (needle[j + k]);
+      b = CANON_ELEMENT (needle[max_suffix_rev + k]);
+      if (b < a)
+        {
+          /* Suffix is smaller, period is entire prefix so far.  */
+          j += k;
+          k = 1;
+          p = j - max_suffix_rev;
+        }
+      else if (a == b)
+        {
+          /* Advance through repetition of the current period.  */
+          if (k != p)
+            ++k;
+          else
+            {
+              j += p;
+              k = 1;
+            }
+        }
+      else /* a < b */
+        {
+          /* Suffix is larger, start over from current location.  */
+          max_suffix_rev = j++;
+          k = p = 1;
+        }
+    }
+
+  /* Choose the shorter suffix.  Return the index of the first byte of
+     the right half, rather than the last byte of the left half.
+
+     For some examples, 'banana' has two critical factorizations, both
+     exposed by the two lexicographic extreme suffixes of 'anana' and
+     'nana', where both suffixes have a period of 2.  On the other
+     hand, with 'aab' and 'bba', both strings have a single critical
+     factorization of the last byte, with the suffix having a period
+     of 1.  While the maximal lexicographic suffix of 'aab' is 'b',
+     the maximal lexicographic suffix of 'bba' is 'ba', which is not a
+     critical factorization.  Conversely, the maximal reverse
+     lexicographic suffix of 'a' works for 'bba', but not 'ab' for
+     'aab'.  The shorter suffix of the two will always be a critical
+     factorization.  */
+  if (max_suffix_rev + 1 < max_suffix + 1)
+    return max_suffix + 1;
+  *period = p;
+  return max_suffix_rev + 1;
+}
+
+/* Return the first location of non-empty NEEDLE within HAYSTACK, or
+   NULL.  HAYSTACK_LEN is the minimum known length of HAYSTACK.  This
+   method is optimized for NEEDLE_LEN < LONG_NEEDLE_THRESHOLD.
+   Performance is guaranteed to be linear, with an initialization cost
+   of 2 * NEEDLE_LEN comparisons.
+
+   If AVAILABLE does not modify HAYSTACK_LEN (as in memmem), then at
+   most 2 * HAYSTACK_LEN - NEEDLE_LEN comparisons occur in searching.
+   If AVAILABLE modifies HAYSTACK_LEN (as in strstr), then at most 3 *
+   HAYSTACK_LEN - NEEDLE_LEN comparisons occur in searching.  */
+static RETURN_TYPE
+two_way_short_needle (const unsigned char *haystack, size_t haystack_len,
+                      const unsigned char *needle, size_t needle_len)
+{
+  size_t i; /* Index into current byte of NEEDLE.  */
+  size_t j; /* Index into current window of HAYSTACK.  */
+  size_t period; /* The period of the right half of needle.  */
+  size_t suffix; /* The index of the right half of needle.  */
+
+  /* Factor the needle into two halves, such that the left half is
+     smaller than the global period, and the right half is
+     periodic (with a period as large as NEEDLE_LEN - suffix).  */
+  suffix = critical_factorization (needle, needle_len, &period);
+
+  /* Perform the search.  Each iteration compares the right half
+     first.  */
+  if (CMP_FUNC (needle, needle + period, suffix) == 0)
+    {
+      /* Entire needle is periodic; a mismatch in the left half can
+         only advance by the period, so use memory to avoid rescanning
+         known occurrences of the period in the right half.  */
+      size_t memory = 0;
+      j = 0;
+      while (AVAILABLE (haystack, haystack_len, j, needle_len))
+        {
+          /* Scan for matches in right half.  */
+          i = MAX (suffix, memory);
+          while (i < needle_len && (CANON_ELEMENT (needle[i])
+                                    == CANON_ELEMENT (haystack[i + j])))
+            ++i;
+          if (needle_len <= i)
+            {
+              /* Scan for matches in left half.  */
+              i = suffix - 1;
+              while (memory < i + 1 && (CANON_ELEMENT (needle[i])
+                                        == CANON_ELEMENT (haystack[i + j])))
+                --i;
+              if (i + 1 < memory + 1)
+                return (RETURN_TYPE) (haystack + j);
+              /* No match, so remember how many repetitions of period
+                 on the right half were scanned.  */
+              j += period;
+              memory = needle_len - period;
+            }
+          else
+            {
+              j += i - suffix + 1;
+              memory = 0;
+            }
+        }
+    }
+  else
+    {
+      /* The two halves of needle are distinct; no extra memory is
+         required, and any mismatch results in a maximal shift.  */
+      period = MAX (suffix, needle_len - suffix) + 1;
+      j = 0;
+      while (AVAILABLE (haystack, haystack_len, j, needle_len))
+        {
+          /* Scan for matches in right half.  */
+          i = suffix;
+          while (i < needle_len && (CANON_ELEMENT (needle[i])
+                                    == CANON_ELEMENT (haystack[i + j])))
+            ++i;
+          if (needle_len <= i)
+            {
+              /* Scan for matches in left half.  */
+              i = suffix - 1;
+              while (i != SIZE_MAX && (CANON_ELEMENT (needle[i])
+                                       == CANON_ELEMENT (haystack[i + j])))
+                --i;
+              if (i == SIZE_MAX)
+                return (RETURN_TYPE) (haystack + j);
+              j += period;
+            }
+          else
+            j += i - suffix + 1;
+        }
+    }
+  return NULL;
+}
+
+/* Return the first location of non-empty NEEDLE within HAYSTACK, or
+   NULL.  HAYSTACK_LEN is the minimum known length of HAYSTACK.  This
+   method is optimized for LONG_NEEDLE_THRESHOLD <= NEEDLE_LEN.
+   Performance is guaranteed to be linear, with an initialization cost
+   of 3 * NEEDLE_LEN + (1 << CHAR_BIT) operations.
+
+   If AVAILABLE does not modify HAYSTACK_LEN (as in memmem), then at
+   most 2 * HAYSTACK_LEN - NEEDLE_LEN comparisons occur in searching,
+   and sublinear performance O(HAYSTACK_LEN / NEEDLE_LEN) is possible.
+   If AVAILABLE modifies HAYSTACK_LEN (as in strstr), then at most 3 *
+   HAYSTACK_LEN - NEEDLE_LEN comparisons occur in searching, and
+   sublinear performance is not possible.  */
+static RETURN_TYPE
+two_way_long_needle (const unsigned char *haystack, size_t haystack_len,
+                     const unsigned char *needle, size_t needle_len)
+{
+  size_t i; /* Index into current byte of NEEDLE.  */
+  size_t j; /* Index into current window of HAYSTACK.  */
+  size_t period; /* The period of the right half of needle.  */
+  size_t suffix; /* The index of the right half of needle.  */
+  size_t shift_table[1U << CHAR_BIT]; /* See below.  */
+
+  /* Factor the needle into two halves, such that the left half is
+     smaller than the global period, and the right half is
+     periodic (with a period as large as NEEDLE_LEN - suffix).  */
+  suffix = critical_factorization (needle, needle_len, &period);
+
+  /* Populate shift_table.  For each possible byte value c,
+     shift_table[c] is the distance from the last occurrence of c to
+     the end of NEEDLE, or NEEDLE_LEN if c is absent from the NEEDLE.
+     shift_table[NEEDLE[NEEDLE_LEN - 1]] contains the only 0.  */
+  for (i = 0; i < 1U << CHAR_BIT; i++)
+    shift_table[i] = needle_len;
+  for (i = 0; i < needle_len; i++)
+    shift_table[CANON_ELEMENT (needle[i])] = needle_len - i - 1;
+
+  /* Perform the search.  Each iteration compares the right half
+     first.  */
+  if (CMP_FUNC (needle, needle + period, suffix) == 0)
+    {
+      /* Entire needle is periodic; a mismatch in the left half can
+         only advance by the period, so use memory to avoid rescanning
+         known occurrences of the period in the right half.  */
+      size_t memory = 0;
+      size_t shift;
+      j = 0;
+      while (AVAILABLE (haystack, haystack_len, j, needle_len))
+        {
+          /* Check the last byte first; if it does not match, then
+             shift to the next possible match location.  */
+          shift = shift_table[CANON_ELEMENT (haystack[j + needle_len - 1])];
+          if (0 < shift)
+            {
+              if (memory && shift < period)
+                {
+                  /* Since needle is periodic, but the last period has
+                     a byte out of place, there can be no match until
+                     after the mismatch.  */
+                  shift = needle_len - period;
+                }
+              memory = 0;
+              j += shift;
+              continue;
+            }
+          /* Scan for matches in right half.  The last byte has
+             already been matched, by virtue of the shift table.  */
+          i = MAX (suffix, memory);
+          while (i < needle_len - 1 && (CANON_ELEMENT (needle[i])
+                                        == CANON_ELEMENT (haystack[i + j])))
+            ++i;
+          if (needle_len - 1 <= i)
+            {
+              /* Scan for matches in left half.  */
+              i = suffix - 1;
+              while (memory < i + 1 && (CANON_ELEMENT (needle[i])
+                                        == CANON_ELEMENT (haystack[i + j])))
+                --i;
+              if (i + 1 < memory + 1)
+                return (RETURN_TYPE) (haystack + j);
+              /* No match, so remember how many repetitions of period
+                 on the right half were scanned.  */
+              j += period;
+              memory = needle_len - period;
+            }
+          else
+            {
+              j += i - suffix + 1;
+              memory = 0;
+            }
+        }
+    }
+  else
+    {
+      /* The two halves of needle are distinct; no extra memory is
+         required, and any mismatch results in a maximal shift.  */
+      size_t shift;
+      period = MAX (suffix, needle_len - suffix) + 1;
+      j = 0;
+      while (AVAILABLE (haystack, haystack_len, j, needle_len))
+        {
+          /* Check the last byte first; if it does not match, then
+             shift to the next possible match location.  */
+          shift = shift_table[CANON_ELEMENT (haystack[j + needle_len - 1])];
+          if (0 < shift)
+            {
+              j += shift;
+              continue;
+            }
+          /* Scan for matches in right half.  The last byte has
+             already been matched, by virtue of the shift table.  */
+          i = suffix;
+          while (i < needle_len - 1 && (CANON_ELEMENT (needle[i])
+                                        == CANON_ELEMENT (haystack[i + j])))
+            ++i;
+          if (needle_len - 1 <= i)
+            {
+              /* Scan for matches in left half.  */
+              i = suffix - 1;
+              while (i != SIZE_MAX && (CANON_ELEMENT (needle[i])
+                                       == CANON_ELEMENT (haystack[i + j])))
+                --i;
+              if (i == SIZE_MAX)
+                return (RETURN_TYPE) (haystack + j);
+              j += period;
+            }
+          else
+            j += i - suffix + 1;
+        }
+    }
+  return NULL;
+}
+
+#undef AVAILABLE
+#undef CANON_ELEMENT
+#undef CMP_FUNC
+#undef MAX
+#undef RETURN_TYPE
-- 
1.8.5.3