text: /*
   * Copyright (c) 2008, 2009, 2010, 2011, 2012 Nicira, Inc.
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at:
   *
   *     http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  #include <config.h>
  #include "util.h"
  #include <assert.h>
  #include <errno.h>
  #include <limits.h>
  #include <stdarg.h>
  #include <stdint.h>
  #include <stdio.h>
  #include <stdlib.h>
  #include <string.h>
  #include <sys/stat.h>
  #include <unistd.h>
  #include "byte-order.h"
  #include "coverage.h"
  #include "openvswitch/types.h"
  #include "vlog.h"
  
  VLOG_DEFINE_THIS_MODULE(util);
  
  COVERAGE_DEFINE(util_xalloc);
  
  /* argv[0] without directory names. */
  const char *program_name;
  
  /* Ordinarily "" but set to "monitor" for a monitor process or "worker" for a
   * worker process. */
  const char *subprogram_name = "";
  
  /* --version option output. */
  static char *program_version;
  
  void
  out_of_memory(void)
  {
      ovs_abort(0, "virtual memory exhausted");
  }
  
  void *
  xcalloc(size_t count, size_t size)
  {
      void *p = count && size ? calloc(count, size) : malloc(1);
      COVERAGE_INC(util_xalloc);
      if (p == NULL) {
          out_of_memory();
      }
      return p;
  }
  
  void *
  xzalloc(size_t size)
  {
      return xcalloc(1, size);
  }
  
  void *
  xmalloc(size_t size)
  {
      void *p = malloc(size ? size : 1);
      COVERAGE_INC(util_xalloc);
      if (p == NULL) {
          out_of_memory();
      }
      return p;
  }
  
  void *
  xrealloc(void *p, size_t size)
  {
      p = realloc(p, size ? size : 1);
      COVERAGE_INC(util_xalloc);
      if (p == NULL) {
          out_of_memory();
      }
      return p;
  }
  
  void *
  xmemdup(const void *p_, size_t size)
  {
      void *p = xmalloc(size);
      memcpy(p, p_, size);
      return p;
  }
  
  char *
  xmemdup0(const char *p_, size_t length)
  {
      char *p = xmalloc(length + 1);
      memcpy(p, p_, length);
      p[length] = '\0';
      return p;
  }
  
  char *
  xstrdup(const char *s)
  {
      return xmemdup0(s, strlen(s));
  }
  
  char *
  xvasprintf(const char *format, va_list args)
  {
      va_list args2;
      size_t needed;
      char *s;
  
      va_copy(args2, args);
      needed = vsnprintf(NULL, 0, format, args);
  
      s = xmalloc(needed + 1);
  
      vsnprintf(s, needed + 1, format, args2);
      va_end(args2);
  
      return s;
  }
  
  void *
  x2nrealloc(void *p, size_t *n, size_t s)
  {
      *n = *n == 0 ? 1 : 2 * *n;
      return xrealloc(p, *n * s);
  }
  
  char *
  xasprintf(const char *format, ...)
  {
      va_list args;
      char *s;
  
      va_start(args, format);
      s = xvasprintf(format, args);
      va_end(args);
  
      return s;
  }
  
  /* Similar to strlcpy() from OpenBSD, but it never reads more than 'size - 1'
   * bytes from 'src' and doesn't return anything. */
  void
  ovs_strlcpy(char *dst, const char *src, size_t size)
  {
      if (size > 0) {
          size_t len = strnlen(src, size - 1);
          memcpy(dst, src, len);
          dst[len] = '\0';
      }
  }
  
  /* Copies 'src' to 'dst'.  Reads no more than 'size - 1' bytes from 'src'.
   * Always null-terminates 'dst' (if 'size' is nonzero), and writes a zero byte
   * to every otherwise unused byte in 'dst'.
   *
   * Except for performance, the following call:
   *     ovs_strzcpy(dst, src, size);
   * is equivalent to these two calls:
   *     memset(dst, '\0', size);
   *     ovs_strlcpy(dst, src, size);
   *
   * (Thus, ovs_strzcpy() is similar to strncpy() without some of the pitfalls.)
   */
  void
  ovs_strzcpy(char *dst, const char *src, size_t size)
  {
      if (size > 0) {
          size_t len = strnlen(src, size - 1);
          memcpy(dst, src, len);
          memset(dst + len, '\0', size - len);
      }
  }
  
  /* Prints 'format' on stderr, formatting it like printf() does.  If 'err_no' is
   * nonzero, then it is formatted with ovs_retval_to_string() and appended to
   * the message inside parentheses.  Then, terminates with abort().
   *
   * This function is preferred to ovs_fatal() in a situation where it would make
   * sense for a monitoring process to restart the daemon.
   *
   * 'format' should not end with a new-line, because this function will add one
   * itself. */
  void
  ovs_abort(int err_no, const char *format, ...)
  {
      va_list args;
  
      va_start(args, format);
      ovs_abort_valist(err_no, format, args);
  }
  
  /* Same as ovs_abort() except that the arguments are supplied as a va_list. */
  void
  ovs_abort_valist(int err_no, const char *format, va_list args)
  {
      ovs_error_valist(err_no, format, args);
      abort();
  }
  
  /* Prints 'format' on stderr, formatting it like printf() does.  If 'err_no' is
   * nonzero, then it is formatted with ovs_retval_to_string() and appended to
   * the message inside parentheses.  Then, terminates with EXIT_FAILURE.
   *
   * 'format' should not end with a new-line, because this function will add one
   * itself. */
  void
  ovs_fatal(int err_no, const char *format, ...)
  {
      va_list args;
  
      va_start(args, format);
      ovs_fatal_valist(err_no, format, args);
  }
  
  /* Same as ovs_fatal() except that the arguments are supplied as a va_list. */
  void
  ovs_fatal_valist(int err_no, const char *format, va_list args)
  {
      ovs_error_valist(err_no, format, args);
      exit(EXIT_FAILURE);
  }
  
  /* Prints 'format' on stderr, formatting it like printf() does.  If 'err_no' is
   * nonzero, then it is formatted with ovs_retval_to_string() and appended to
   * the message inside parentheses.
   *
   * 'format' should not end with a new-line, because this function will add one
   * itself. */
  void
  ovs_error(int err_no, const char *format, ...)
  {
      va_list args;
  
      va_start(args, format);
      ovs_error_valist(err_no, format, args);
      va_end(args);
  }
  
  /* Same as ovs_error() except that the arguments are supplied as a va_list. */
  void
  ovs_error_valist(int err_no, const char *format, va_list args)
  {
      int save_errno = errno;
  
      if (subprogram_name[0]) {
          fprintf(stderr, "%s(%s): ", program_name, subprogram_name);
      } else {
          fprintf(stderr, "%s: ", program_name);
      }
  
      vfprintf(stderr, format, args);
      if (err_no != 0) {
          fprintf(stderr, " (%s)", ovs_retval_to_string(err_no));
      }
      putc('\n', stderr);
  
      errno = save_errno;
  }
  
  /* Many OVS functions return an int which is one of:
   * - 0: no error yet
   * - >0: errno value
   * - EOF: end of file (not necessarily an error; depends on the function called)
   *
   * Returns the appropriate human-readable string. The caller must copy the
   * string if it wants to hold onto it, as the storage may be overwritten on
   * subsequent function calls.
   */
  const char *
  ovs_retval_to_string(int retval)
  {
      static char unknown[48];
  
      if (!retval) {
          return "";
      }
      if (retval > 0) {
          return strerror(retval);
      }
      if (retval == EOF) {
          return "End of file";
      }
      snprintf(unknown, sizeof unknown, "***unknown return value: %d***", retval);
      return unknown;
  }
  
  /* Sets global "program_name" and "program_version" variables.  Should
   * be called at the beginning of main() with "argv[0]" as the argument
   * to 'argv0'.
   *
   * 'version' should contain the version of the caller's program.  If 'version'
   * is the same as the VERSION #define, the caller is assumed to be part of Open
   * vSwitch.  Otherwise, it is assumed to be an external program linking against
   * the Open vSwitch libraries.
   *
   * The 'date' and 'time' arguments should likely be called with
   * "__DATE__" and "__TIME__" to use the time the binary was built.
   * Alternatively, the "set_program_name" macro may be called to do this
   * automatically.
   */
  void
  set_program_name__(const char *argv0, const char *version, const char *date,
                     const char *time)
  {
      const char *slash = strrchr(argv0, '/');
      program_name = slash ? slash + 1 : argv0;
  
      free(program_version);
  
      if (!strcmp(version, VERSION)) {
          program_version = xasprintf("%s (Open vSwitch) "VERSION"\n"
                                      "Compiled %s %s\n",
                                      program_name, date, time);
      } else {
          program_version = xasprintf("%s %s\n"
                                      "Open vSwitch Library "VERSION"\n"
                                      "Compiled %s %s\n",
                                      program_name, version, date, time);
      }
  }
  
  /* Returns a pointer to a string describing the program version.  The
   * caller must not modify or free the returned string.
   */
  const char *
  get_program_version(void)
  {
      return program_version;
  }
  
  /* Print the version information for the program.  */
  void
  ovs_print_version(uint8_t min_ofp, uint8_t max_ofp)
  {
      printf("%s", program_version);
      if (min_ofp || max_ofp) {
          printf("OpenFlow versions %#x:%#x\n", min_ofp, max_ofp);
      }
  }
  
  /* Writes the 'size' bytes in 'buf' to 'stream' as hex bytes arranged 16 per
   * line.  Numeric offsets are also included, starting at 'ofs' for the first
   * byte in 'buf'.  If 'ascii' is true then the corresponding ASCII characters
   * are also rendered alongside. */
  void
  ovs_hex_dump(FILE *stream, const void *buf_, size_t size,
               uintptr_t ofs, bool ascii)
  {
    const uint8_t *buf = buf_;
    const size_t per_line = 16; /* Maximum bytes per line. */
  
    while (size > 0)
      {
        size_t start, end, n;
        size_t i;
  
        /* Number of bytes on this line. */
        start = ofs % per_line;
        end = per_line;
        if (end - start > size)
          end = start + size;
        n = end - start;
  
        /* Print line. */
        fprintf(stream, "%08jx  ", (uintmax_t) ROUND_DOWN(ofs, per_line));
        for (i = 0; i < start; i++)
          fprintf(stream, "   ");
        for (; i < end; i++)
          fprintf(stream, "%02hhx%c",
                  buf[i - start], i == per_line / 2 - 1? '-' : ' ');
        if (ascii)
          {
            for (; i < per_line; i++)
              fprintf(stream, "   ");
            fprintf(stream, "|");
            for (i = 0; i < start; i++)
              fprintf(stream, " ");
            for (; i < end; i++) {
                int c = buf[i - start];
                putc(c >= 32 && c < 127 ? c : '.', stream);
            }
            for (; i < per_line; i++)
              fprintf(stream, " ");
            fprintf(stream, "|");
          }
        fprintf(stream, "\n");
  
        ofs += n;
        buf += n;
        size -= n;
      }
  }
  
  bool
  str_to_int(const char *s, int base, int *i)
  {
      long long ll;
      bool ok = str_to_llong(s, base, &ll);
      *i = ll;
      return ok;
  }
  
  bool
  str_to_long(const char *s, int base, long *li)
  {
      long long ll;
      bool ok = str_to_llong(s, base, &ll);
      *li = ll;
      return ok;
  }
  
  bool
  str_to_llong(const char *s, int base, long long *x)
  {
      int save_errno = errno;
      char *tail;
      errno = 0;
      *x = strtoll(s, &tail, base);
      if (errno == EINVAL || errno == ERANGE || tail == s || *tail != '\0') {
          errno = save_errno;
          *x = 0;
          return false;
      } else {
          errno = save_errno;
          return true;
      }
  }
  
  bool
  str_to_uint(const char *s, int base, unsigned int *u)
  {
      return str_to_int(s, base, (int *) u);
  }
  
  bool
  str_to_ulong(const char *s, int base, unsigned long *ul)
  {
      return str_to_long(s, base, (long *) ul);
  }
  
  bool
  str_to_ullong(const char *s, int base, unsigned long long *ull)
  {
      return str_to_llong(s, base, (long long *) ull);
  }
  
  /* Converts floating-point string 's' into a double.  If successful, stores
   * the double in '*d' and returns true; on failure, stores 0 in '*d' and
   * returns false.
   *
   * Underflow (e.g. "1e-9999") is not considered an error, but overflow
   * (e.g. "1e9999)" is. */
  bool
  str_to_double(const char *s, double *d)
  {
      int save_errno = errno;
      char *tail;
      errno = 0;
      *d = strtod(s, &tail);
      if (errno == EINVAL || (errno == ERANGE && *d != 0)
          || tail == s || *tail != '\0') {
          errno = save_errno;
          *d = 0;
          return false;
      } else {
          errno = save_errno;
          return true;
      }
  }
  
  /* Returns the value of 'c' as a hexadecimal digit. */
  int
  hexit_value(int c)
  {
      switch (c) {
      case '0': case '1': case '2': case '3': case '4':
      case '5': case '6': case '7': case '8': case '9':
          return c - '0';
  
      case 'a': case 'A':
          return 0xa;
  
      case 'b': case 'B':
          return 0xb;
  
      case 'c': case 'C':
          return 0xc;
  
      case 'd': case 'D':
          return 0xd;
  
      case 'e': case 'E':
          return 0xe;
  
      case 'f': case 'F':
          return 0xf;
  
      default:
          return -1;
      }
  }
  
  /* Returns the integer value of the 'n' hexadecimal digits starting at 's', or
   * UINT_MAX if one of those "digits" is not really a hex digit.  If 'ok' is
   * nonnull, '*ok' is set to true if the conversion succeeds or to false if a
   * non-hex digit is detected. */
  unsigned int
  hexits_value(const char *s, size_t n, bool *ok)
  {
      unsigned int value;
      size_t i;
  
      value = 0;
      for (i = 0; i < n; i++) {
          int hexit = hexit_value(s[i]);
          if (hexit < 0) {
              if (ok) {
                  *ok = false;
              }
              return UINT_MAX;
          }
          value = (value << 4) + hexit;
      }
      if (ok) {
          *ok = true;
      }
      return value;
  }
  
  /* Returns the current working directory as a malloc()'d string, or a null
   * pointer if the current working directory cannot be determined. */
  char *
  get_cwd(void)
  {
      long int path_max;
      size_t size;
  
      /* Get maximum path length or at least a reasonable estimate. */
      path_max = pathconf(".", _PC_PATH_MAX);
      size = (path_max < 0 ? 1024
              : path_max > 10240 ? 10240
              : path_max);
  
      /* Get current working directory. */
      for (;;) {
          char *buf = xmalloc(size);
          if (getcwd(buf, size)) {
              return xrealloc(buf, strlen(buf) + 1);
          } else {
              int error = errno;
              free(buf);
              if (error != ERANGE) {
                  VLOG_WARN("getcwd failed (%s)", strerror(error));
                  return NULL;
              }
              size *= 2;
          }
      }
  }
  
  static char *
  all_slashes_name(const char *s)
  {
      return xstrdup(s[0] == '/' && s[1] == '/' && s[2] != '/' ? "//"
                     : s[0] == '/' ? "/"
                     : ".");
  }
  
  /* Returns the directory name portion of 'file_name' as a malloc()'d string,
   * similar to the POSIX dirname() function but thread-safe. */
  char *
  dir_name(const char *file_name)
  {
      size_t len = strlen(file_name);
      while (len > 0 && file_name[len - 1] == '/') {
          len--;
      }
      while (len > 0 && file_name[len - 1] != '/') {
          len--;
      }
      while (len > 0 && file_name[len - 1] == '/') {
          len--;
      }
      return len ? xmemdup0(file_name, len) : all_slashes_name(file_name);
  }
  
  /* Returns the file name portion of 'file_name' as a malloc()'d string,
   * similar to the POSIX basename() function but thread-safe. */
  char *
  base_name(const char *file_name)
  {
      size_t end, start;
  
      end = strlen(file_name);
      while (end > 0 && file_name[end - 1] == '/') {
          end--;
      }
  
      if (!end) {
          return all_slashes_name(file_name);
      }
  
      start = end;
      while (start > 0 && file_name[start - 1] != '/') {
          start--;
      }
  
      return xmemdup0(file_name + start, end - start);
  }
  
  /* If 'file_name' starts with '/', returns a copy of 'file_name'.  Otherwise,
   * returns an absolute path to 'file_name' considering it relative to 'dir',
   * which itself must be absolute.  'dir' may be null or the empty string, in
   * which case the current working directory is used.
   *
   * Returns a null pointer if 'dir' is null and getcwd() fails. */
  char *
  abs_file_name(const char *dir, const char *file_name)
  {
      if (file_name[0] == '/') {
          return xstrdup(file_name);
      } else if (dir && dir[0]) {
          char *separator = dir[strlen(dir) - 1] == '/' ? "" : "/";
          return xasprintf("%s%s%s", dir, separator, file_name);
      } else {
          char *cwd = get_cwd();
          if (cwd) {
              char *abs_name = xasprintf("%s/%s", cwd, file_name);
              free(cwd);
              return abs_name;
          } else {
              return NULL;
          }
      }
  }
  
  /* Like readlink(), but returns the link name as a null-terminated string in
   * allocated memory that the caller must eventually free (with free()).
   * Returns NULL on error, in which case errno is set appropriately. */
  char *
  xreadlink(const char *filename)
  {
      size_t size;
  
      for (size = 64; ; size *= 2) {
          char *buf = xmalloc(size);
          ssize_t retval = readlink(filename, buf, size);
          int error = errno;
  
          if (retval >= 0 && retval < size) {
              buf[retval] = '\0';
              return buf;
          }
  
          free(buf);
          if (retval < 0) {
              errno = error;
              return NULL;
          }
      }
  }
  
  /* Returns a version of 'filename' with symlinks in the final component
   * dereferenced.  This differs from realpath() in that:
   *
   *     - 'filename' need not exist.
   *
   *     - If 'filename' does exist as a symlink, its referent need not exist.
   *
   *     - Only symlinks in the final component of 'filename' are dereferenced.
   *
   * The caller must eventually free the returned string (with free()). */
  char *
  follow_symlinks(const char *filename)
  {
      struct stat s;
      char *fn;
      int i;
  
      fn = xstrdup(filename);
      for (i = 0; i < 10; i++) {
          char *linkname;
          char *next_fn;
  
          if (lstat(fn, &s) != 0 || !S_ISLNK(s.st_mode)) {
              return fn;
          }
  
          linkname = xreadlink(fn);
          if (!linkname) {
              VLOG_WARN("%s: readlink failed (%s)", filename, strerror(errno));
              return fn;
          }
  
          if (linkname[0] == '/') {
              /* Target of symlink is absolute so use it raw. */
              next_fn = linkname;
          } else {
              /* Target of symlink is relative so add to 'fn''s directory. */
              char *dir = dir_name(fn);
  
              if (!strcmp(dir, ".")) {
                  next_fn = linkname;
              } else {
                  char *separator = dir[strlen(dir) - 1] == '/' ? "" : "/";
                  next_fn = xasprintf("%s%s%s", dir, separator, linkname);
                  free(linkname);
              }
  
              free(dir);
          }
  
          free(fn);
          fn = next_fn;
      }
  
      VLOG_WARN("%s: too many levels of symlinks", filename);
      free(fn);
      return xstrdup(filename);
  }
  
  /* Pass a value to this function if it is marked with
   * __attribute__((warn_unused_result)) and you genuinely want to ignore
   * its return value.  (Note that every scalar type can be implicitly
   * converted to bool.) */
  void ignore(bool x OVS_UNUSED) { }
  
  /* Returns an appropriate delimiter for inserting just before the 0-based item
   * 'index' in a list that has 'total' items in it. */
  const char *
  english_list_delimiter(size_t index, size_t total)
  {
      return (index == 0 ? ""
              : index < total - 1 ? ", "
              : total > 2 ? ", and "
              : " and ");
  }
  
  /* Given a 32 bit word 'n', calculates floor(log_2('n')).  This is equivalent
   * to finding the bit position of the most significant one bit in 'n'.  It is
   * an error to call this function with 'n' == 0. */
  int
  log_2_floor(uint32_t n)
  {
      assert(n);
  
  #if !defined(UINT_MAX) || !defined(UINT32_MAX)
  #error "Someone screwed up the #includes."
  #elif __GNUC__ >= 4 && UINT_MAX == UINT32_MAX
      return 31 - __builtin_clz(n);
  #else
      {
          int log = 0;
  
  #define BIN_SEARCH_STEP(BITS)                   \
          if (n >= (1 << BITS)) {                 \
              log += BITS;                        \
              n >>= BITS;                         \
          }
          BIN_SEARCH_STEP(16);
          BIN_SEARCH_STEP(8);
          BIN_SEARCH_STEP(4);
          BIN_SEARCH_STEP(2);
          BIN_SEARCH_STEP(1);
  #undef BIN_SEARCH_STEP
          return log;
      }
  #endif
  }
  
  /* Given a 32 bit word 'n', calculates ceil(log_2('n')).  It is an error to
   * call this function with 'n' == 0. */
  int
  log_2_ceil(uint32_t n)
  {
      return log_2_floor(n) + !IS_POW2(n);
  }
  
  /* Returns the number of trailing 0-bits in 'n', or 32 if 'n' is 0. */
  int
  ctz(uint32_t n)
  {
      if (!n) {
          return 32;
      } else {
  #if !defined(UINT_MAX) || !defined(UINT32_MAX)
  #error "Someone screwed up the #includes."
  #elif __GNUC__ >= 4 && UINT_MAX == UINT32_MAX
          return __builtin_ctz(n);
  #else
          unsigned int k;
          int count = 31;
  
  #define CTZ_STEP(X)                             \
          k = n << (X);                           \
          if (k) {                                \
              count -= X;                         \
              n = k;                              \
          }
          CTZ_STEP(16);
          CTZ_STEP(8);
          CTZ_STEP(4);
          CTZ_STEP(2);
          CTZ_STEP(1);
  #undef CTZ_STEP
  
          return count;
  #endif
      }
  }
  
  /* Returns true if the 'n' bytes starting at 'p' are zeros. */
  bool
  is_all_zeros(const uint8_t *p, size_t n)
  {
      size_t i;
  
      for (i = 0; i < n; i++) {
          if (p[i] != 0x00) {
              return false;
          }
      }
      return true;
  }
  
  /* Returns true if the 'n' bytes starting at 'p' are 0xff. */
  bool
  is_all_ones(const uint8_t *p, size_t n)
  {
      size_t i;
  
      for (i = 0; i < n; i++) {
          if (p[i] != 0xff) {
              return false;
          }
      }
      return true;
  }
  
  /* Copies 'n_bits' bits starting from bit 'src_ofs' in 'src' to the 'n_bits'
   * starting from bit 'dst_ofs' in 'dst'.  'src' is 'src_len' bytes long and
   * 'dst' is 'dst_len' bytes long.
   *
   * If you consider all of 'src' to be a single unsigned integer in network byte
   * order, then bit N is the bit with value 2**N.  That is, bit 0 is the bit
   * with value 1 in src[src_len - 1], bit 1 is the bit with value 2, bit 2 is
   * the bit with value 4, ..., bit 8 is the bit with value 1 in src[src_len -
   * 2], and so on.  Similarly for 'dst'.
   *
   * Required invariants:
   *   src_ofs + n_bits <= src_len * 8
   *   dst_ofs + n_bits <= dst_len * 8
   *   'src' and 'dst' must not overlap.
   */
  void
  bitwise_copy(const void *src_, unsigned int src_len, unsigned int src_ofs,
               void *dst_, unsigned int dst_len, unsigned int dst_ofs,
               unsigned int n_bits)
  {
      const uint8_t *src = src_;
      uint8_t *dst = dst_;
  
      src += src_len - (src_ofs / 8 + 1);
      src_ofs %= 8;
  
      dst += dst_len - (dst_ofs / 8 + 1);
      dst_ofs %= 8;
  
      if (src_ofs == 0 && dst_ofs == 0) {
          unsigned int n_bytes = n_bits / 8;
          if (n_bytes) {
              dst -= n_bytes - 1;
              src -= n_bytes - 1;
              memcpy(dst, src, n_bytes);
  
              n_bits %= 8;
              src--;
              dst--;
          }
          if (n_bits) {
              uint8_t mask = (1 << n_bits) - 1;
              *dst = (*dst & ~mask) | (*src & mask);
          }
      } else {
          while (n_bits > 0) {
              unsigned int max_copy = 8 - MAX(src_ofs, dst_ofs);
              unsigned int chunk = MIN(n_bits, max_copy);
              uint8_t mask = ((1 << chunk) - 1) << dst_ofs;
  
              *dst &= ~mask;
              *dst |= ((*src >> src_ofs) << dst_ofs) & mask;
  
              src_ofs += chunk;
              if (src_ofs == 8) {
                  src--;
                  src_ofs = 0;
              }
              dst_ofs += chunk;
              if (dst_ofs == 8) {
                  dst--;
                  dst_ofs = 0;
              }
              n_bits -= chunk;
          }
      }
  }
  
  /* Zeros the 'n_bits' bits starting from bit 'dst_ofs' in 'dst'.  'dst' is
   * 'dst_len' bytes long.
   *
   * If you consider all of 'dst' to be a single unsigned integer in network byte
   * order, then bit N is the bit with value 2**N.  That is, bit 0 is the bit
   * with value 1 in dst[dst_len - 1], bit 1 is the bit with value 2, bit 2 is
   * the bit with value 4, ..., bit 8 is the bit with value 1 in dst[dst_len -
   * 2], and so on.
   *
   * Required invariant:
   *   dst_ofs + n_bits <= dst_len * 8
   */
  void
  bitwise_zero(void *dst_, unsigned int dst_len, unsigned dst_ofs,
               unsigned int n_bits)
  {
      uint8_t *dst = dst_;
  
      if (!n_bits) {
          return;
      }
  
      dst += dst_len - (dst_ofs / 8 + 1);
      dst_ofs %= 8;
  
      if (dst_ofs) {
          unsigned int chunk = MIN(n_bits, 8 - dst_ofs);
  
          *dst &= ~(((1 << chunk) - 1) << dst_ofs);
  
          n_bits -= chunk;
          if (!n_bits) {
              return;
          }
  
          dst--;
      }
  
      while (n_bits >= 8) {
          *dst-- = 0;
          n_bits -= 8;
      }
  
      if (n_bits) {
          *dst &= ~((1 << n_bits) - 1);
      }
  }
  
  /* Sets to 1 all of the 'n_bits' bits starting from bit 'dst_ofs' in 'dst'.
   * 'dst' is 'dst_len' bytes long.
   *
   * If you consider all of 'dst' to be a single unsigned integer in network byte
   * order, then bit N is the bit with value 2**N.  That is, bit 0 is the bit
   * with value 1 in dst[dst_len - 1], bit 1 is the bit with value 2, bit 2 is
   * the bit with value 4, ..., bit 8 is the bit with value 1 in dst[dst_len -
   * 2], and so on.
   *
   * Required invariant:
   *   dst_ofs + n_bits <= dst_len * 8
   */
  void
  bitwise_one(void *dst_, unsigned int dst_len, unsigned dst_ofs,
              unsigned int n_bits)
  {
      uint8_t *dst = dst_;
  
      if (!n_bits) {
          return;
      }
  
      dst += dst_len - (dst_ofs / 8 + 1);
      dst_ofs %= 8;
  
      if (dst_ofs) {
          unsigned int chunk = MIN(n_bits, 8 - dst_ofs);
  
          *dst |= ((1 << chunk) - 1) << dst_ofs;
  
          n_bits -= chunk;
          if (!n_bits) {
              return;
          }
  
          dst--;
      }
  
      while (n_bits >= 8) {
          *dst-- = 0xff;
          n_bits -= 8;
      }
  
      if (n_bits) {
          *dst |= (1 << n_bits) - 1;
      }
  }
  
  /* Scans the 'n_bits' bits starting from bit 'dst_ofs' in 'dst' for 1-bits.
   * Returns false if any 1-bits are found, otherwise true.  'dst' is 'dst_len'
   * bytes long.
   *
   * If you consider all of 'dst' to be a single unsigned integer in network byte
   * order, then bit N is the bit with value 2**N.  That is, bit 0 is the bit
   * with value 1 in dst[dst_len - 1], bit 1 is the bit with value 2, bit 2 is
   * the bit with value 4, ..., bit 8 is the bit with value 1 in dst[dst_len -
   * 2], and so on.
   *
   * Required invariant:
   *   dst_ofs + n_bits <= dst_len * 8
   */
  bool
  bitwise_is_all_zeros(const void *p_, unsigned int len, unsigned int ofs,
                       unsigned int n_bits)
  {
      const uint8_t *p = p_;
  
      if (!n_bits) {
          return true;
      }
  
      p += len - (ofs / 8 + 1);
      ofs %= 8;
  
      if (ofs) {
          unsigned int chunk = MIN(n_bits, 8 - ofs);
  
          if (*p & (((1 << chunk) - 1) << ofs)) {
              return false;
          }
  
          n_bits -= chunk;
          if (!n_bits) {
              return true;
          }
  
          p--;
      }
  
      while (n_bits >= 8) {
          if (*p) {
              return false;
          }
          n_bits -= 8;
          p--;
      }
  
      if (n_bits && *p & ((1 << n_bits) - 1)) {
          return false;
      }
  
      return true;
  }
  
  /* Copies the 'n_bits' low-order bits of 'value' into the 'n_bits' bits
   * starting at bit 'dst_ofs' in 'dst', which is 'dst_len' bytes long.
   *
   * If you consider all of 'dst' to be a single unsigned integer in network byte
   * order, then bit N is the bit with value 2**N.  That is, bit 0 is the bit
   * with value 1 in dst[dst_len - 1], bit 1 is the bit with value 2, bit 2 is
   * the bit with value 4, ..., bit 8 is the bit with value 1 in dst[dst_len -
   * 2], and so on.
   *
   * Required invariants:
   *   dst_ofs + n_bits <= dst_len * 8
   *   n_bits <= 64
   */
  void
  bitwise_put(uint64_t value,
              void *dst, unsigned int dst_len, unsigned int dst_ofs,
              unsigned int n_bits)
  {
      ovs_be64 n_value = htonll(value);
      bitwise_copy(&n_value, sizeof n_value, 0,
                   dst, dst_len, dst_ofs,
                   n_bits);
  }
  
  /* Returns the value of the 'n_bits' bits starting at bit 'src_ofs' in 'src',
   * which is 'src_len' bytes long.
   *
   * If you consider all of 'src' to be a single unsigned integer in network byte
   * order, then bit N is the bit with value 2**N.  That is, bit 0 is the bit
   * with value 1 in src[src_len - 1], bit 1 is the bit with value 2, bit 2 is
   * the bit with value 4, ..., bit 8 is the bit with value 1 in src[src_len -
   * 2], and so on.
   *
   * Required invariants:
   *   src_ofs + n_bits <= src_len * 8
   *   n_bits <= 64
   */
  uint64_t
  bitwise_get(const void *src, unsigned int src_len,
              unsigned int src_ofs, unsigned int n_bits)
  {
      ovs_be64 value = htonll(0);
  
      bitwise_copy(src, src_len, src_ofs,
                   &value, sizeof value, 0,
                   n_bits);
      return ntohll(value);
  }
  