Patch #6441. Reviewed by John Darrington.

[pspp-builds.git] / src / libpspp / str.c

/* PSPP - a program for statistical analysis.
   Copyright (C) 1997-9, 2000, 2006 Free Software Foundation, Inc.

   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 3 of the License, 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/>. */

#include <config.h>

#include "str.h"

#include <ctype.h>
#include <errno.h>
#include <stdint.h>
#include <stdlib.h>

#include <libpspp/message.h>
#include <libpspp/pool.h>

#include "minmax.h"
#include "xalloc.h"
#include "xsize.h"
\f
/* Reverses the order of NBYTES bytes at address P, thus converting
   between little- and big-endian byte orders.  */
void
buf_reverse (char *p, size_t nbytes)
{
  char *h = p, *t = &h[nbytes - 1];
  char temp;

  nbytes /= 2;
  while (nbytes--)
    {
      temp = *h;
      *h++ = *t;
      *t-- = temp;
    }
}

/* Finds the last NEEDLE of length NEEDLE_LEN in a HAYSTACK of length
   HAYSTACK_LEN.  Returns a pointer to the needle found. */
char *
buf_find_reverse (const char *haystack, size_t haystack_len,
                 const char *needle, size_t needle_len)
{
  int i;
  for (i = haystack_len - needle_len; i >= 0; i--)
    if (!memcmp (needle, &haystack[i], needle_len))
      return (char *) &haystack[i];
  return 0;
}

/* Compares the SIZE bytes in A to those in B, disregarding case,
   and returns a strcmp()-type result. */
int
buf_compare_case (const char *a_, const char *b_, size_t size)
{
  const unsigned char *a = (unsigned char *) a_;
  const unsigned char *b = (unsigned char *) b_;

  while (size-- > 0)
    {
      unsigned char ac = toupper (*a++);
      unsigned char bc = toupper (*b++);

      if (ac != bc)
        return ac > bc ? 1 : -1;
    }

  return 0;
}

/* Compares A of length A_LEN to B of length B_LEN.  The shorter
   string is considered to be padded with spaces to the length of
   the longer. */
int
buf_compare_rpad (const char *a, size_t a_len, const char *b, size_t b_len)
{
  size_t min_len;
  int result;

  min_len = a_len < b_len ? a_len : b_len;
  result = memcmp (a, b, min_len);
  if (result != 0)
    return result;
  else
    {
      size_t idx;

      if (a_len < b_len)
        {
          for (idx = min_len; idx < b_len; idx++)
            if (' ' != b[idx])
              return ' ' > b[idx] ? 1 : -1;
        }
      else
        {
          for (idx = min_len; idx < a_len; idx++)
            if (a[idx] != ' ')
              return a[idx] > ' ' ? 1 : -1;
        }
      return 0;
    }
}

/* Compares strin A to string B.  The shorter string is
   considered to be padded with spaces to the length of the
   longer. */
int
str_compare_rpad (const char *a, const char *b)
{
  return buf_compare_rpad (a, strlen (a), b, strlen (b));
}

/* Copies string SRC to buffer DST, of size DST_SIZE bytes.
   DST is truncated to DST_SIZE bytes or padded on the right with
   spaces as needed. */
void
buf_copy_str_rpad (char *dst, size_t dst_size, const char *src)
{
  size_t src_len = strlen (src);
  if (src_len >= dst_size)
    memcpy (dst, src, dst_size);
  else
    {
      memcpy (dst, src, src_len);
      memset (&dst[src_len], ' ', dst_size - src_len);
    }
}

/* Copies string SRC to buffer DST, of size DST_SIZE bytes.
   DST is truncated to DST_SIZE bytes or padded on the left with
   spaces as needed. */
void
buf_copy_str_lpad (char *dst, size_t dst_size, const char *src)
{
  size_t src_len = strlen (src);
  if (src_len >= dst_size)
    memcpy (dst, src, dst_size);
  else
    {
      size_t pad_cnt = dst_size - src_len;
      memset (&dst[0], ' ', pad_cnt);
      memcpy (dst + pad_cnt, src, src_len);
    }
}

/* Copies buffer SRC, of SRC_SIZE bytes, to DST, of DST_SIZE bytes.
   DST is truncated to DST_SIZE bytes or padded on the left with
   spaces as needed. */
void
buf_copy_lpad (char *dst, size_t dst_size,
               const char *src, size_t src_size)
{
  if (src_size >= dst_size)
    memmove (dst, src, dst_size);
  else
    {
      memset (dst, ' ', dst_size - src_size);
      memmove (&dst[dst_size - src_size], src, src_size);
    }
}

/* Copies buffer SRC, of SRC_SIZE bytes, to DST, of DST_SIZE bytes.
   DST is truncated to DST_SIZE bytes or padded on the right with
   spaces as needed. */
void
buf_copy_rpad (char *dst, size_t dst_size,
               const char *src, size_t src_size)
{
  if (src_size >= dst_size)
    memmove (dst, src, dst_size);
  else
    {
      memmove (dst, src, src_size);
      memset (&dst[src_size], ' ', dst_size - src_size);
    }
}

/* Copies string SRC to string DST, which is in a buffer DST_SIZE
   bytes long.
   Truncates DST to DST_SIZE - 1 characters or right-pads with
   spaces to DST_SIZE - 1 characters if necessary. */
void
str_copy_rpad (char *dst, size_t dst_size, const char *src)
{
  size_t src_len = strlen (src);
  if (src_len < dst_size - 1)
    {
      memcpy (dst, src, src_len);
      memset (&dst[src_len], ' ', dst_size - 1 - src_len);
    }
  else
    memcpy (dst, src, dst_size - 1);
  dst[dst_size - 1] = 0;
}

/* Copies SRC to DST, which is in a buffer DST_SIZE bytes long.
   Truncates DST to DST_SIZE - 1 characters, if necessary. */
void
str_copy_trunc (char *dst, size_t dst_size, const char *src)
{
  size_t src_len = strlen (src);
  assert (dst_size > 0);
  if (src_len + 1 < dst_size)
    memcpy (dst, src, src_len + 1);
  else
    {
      memcpy (dst, src, dst_size - 1);
      dst[dst_size - 1] = '\0';
    }
}

/* Copies buffer SRC, of SRC_LEN bytes,
   to DST, which is in a buffer DST_SIZE bytes long.
   Truncates DST to DST_SIZE - 1 characters, if necessary. */
void
str_copy_buf_trunc (char *dst, size_t dst_size,
                    const char *src, size_t src_size)
{
  size_t dst_len;
  assert (dst_size > 0);

  dst_len = src_size < dst_size ? src_size : dst_size - 1;
  memcpy (dst, src, dst_len);
  dst[dst_len] = '\0';
}

/* Converts each character in S to uppercase. */
void
str_uppercase (char *s)
{
  for (; *s != '\0'; s++)
    *s = toupper ((unsigned char) *s);
}

/* Converts each character in S to lowercase. */
void
str_lowercase (char *s)
{
  for (; *s != '\0'; s++)
    *s = tolower ((unsigned char) *s);
}

/* Converts NUMBER into a string in 26-adic notation in BUFFER,
   which has room for SIZE bytes.  Returns true if successful,
   false if NUMBER, plus a trailing null, is too large to fit in
   the available space.

   26-adic notation is "spreadsheet column numbering": 1 = A, 2 =
   B, 3 = C, ... 26 = Z, 27 = AA, 28 = AB, 29 = AC, ...

   26-adic notation is the special case of a k-adic numeration
   system (aka bijective base-k numeration) with k=26.  In k-adic
   numeration, the digits are {1, 2, 3, ..., k} (there is no
   digit 0), and integer 0 is represented by the empty string.
   For more information, see
   http://en.wikipedia.org/wiki/Bijective_numeration. */
bool
str_format_26adic (unsigned long int number, char buffer[], size_t size)
{
  size_t length = 0;

  while (number-- > 0)
    {
      if (length >= size)
        return false;
      buffer[length++] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"[number % 26];
      number /= 26;
    }

  if (length >= size)
    return false;
  buffer[length] = '\0';

  buf_reverse (buffer, length);
  return true;
}

/* Formats FORMAT into DST, as with sprintf(), and returns the
   address of the terminating null written to DST. */
char *
spprintf (char *dst, const char *format, ...)
{
  va_list args;
  int count;

  va_start (args, format);
  count = vsprintf (dst, format, args);
  va_end (args);

  return dst + count;
}

/* Sets the SIZE bytes starting at BLOCK to C,
   and returns the byte following BLOCK. */
void *
mempset (void *block, int c, size_t size)
{
  memset (block, c, size);
  return (char *) block + size;
}
\f
/* Substrings. */

/* Returns an empty substring. */
struct substring
ss_empty (void)
{
  struct substring ss;
  ss.string = NULL;
  ss.length = 0;
  return ss;
}

/* Returns a substring whose contents are the given C-style
   string CSTR. */
struct substring
ss_cstr (const char *cstr)
{
  return ss_buffer (cstr, strlen (cstr));
}

/* Returns a substring whose contents are the CNT characters in
   BUFFER. */
struct substring
ss_buffer (const char *buffer, size_t cnt)
{
  struct substring ss;
  ss.string = (char *) buffer;
  ss.length = cnt;
  return ss;
}

/* Returns a substring whose contents are the CNT characters
   starting at the (0-based) position START in SS. */
struct substring
ss_substr (struct substring ss, size_t start, size_t cnt)
{
  if (start < ss.length)
    return ss_buffer (ss.string + start, MIN (cnt, ss.length - start));
  else
    return ss_buffer (ss.string + ss.length, 0);
}

/* Returns a substring whose contents are the first CNT
   characters in SS. */
struct substring
ss_head (struct substring ss, size_t cnt)
{
  return ss_buffer (ss.string, MIN (cnt, ss.length));
}

/* Returns a substring whose contents are the last CNT characters
   in SS. */
struct substring
ss_tail (struct substring ss, size_t cnt)
{
  if (cnt < ss.length)
    return ss_buffer (ss.string + (ss.length - cnt), cnt);
  else
    return ss;
}

/* Makes a malloc()'d copy of the contents of OLD
   and stores it in NEW. */
void
ss_alloc_substring (struct substring *new, struct substring old)
{
  new->string = xmalloc (old.length);
  new->length = old.length;
  memcpy (new->string, old.string, old.length);
}

/* Allocates room for a CNT-character string in NEW. */
void
ss_alloc_uninit (struct substring *new, size_t cnt)
{
  new->string = xmalloc (cnt);
  new->length = cnt;
}

/* Makes a pool_alloc_unaligned()'d copy of the contents of OLD
   in POOL, and stores it in NEW. */
void
ss_alloc_substring_pool (struct substring *new, struct substring old,
                         struct pool *pool)
{
  new->string = pool_alloc_unaligned (pool, old.length);
  new->length = old.length;
  memcpy (new->string, old.string, old.length);
}

/* Allocates room for a CNT-character string in NEW in POOL. */
void
ss_alloc_uninit_pool (struct substring *new, size_t cnt, struct pool *pool)
{
  new->string = pool_alloc_unaligned (pool, cnt);
  new->length = cnt;
}

/* Frees the string that SS points to. */
void
ss_dealloc (struct substring *ss)
{
  free (ss->string);
}

/* Truncates SS to at most CNT characters in length. */
void
ss_truncate (struct substring *ss, size_t cnt)
{
  if (ss->length > cnt)
    ss->length = cnt;
}

/* Removes trailing characters in TRIM_SET from SS.
   Returns number of characters removed. */
size_t
ss_rtrim (struct substring *ss, struct substring trim_set)
{
  size_t cnt = 0;
  while (cnt < ss->length
         && ss_find_char (trim_set,
                          ss->string[ss->length - cnt - 1]) != SIZE_MAX)
    cnt++;
  ss->length -= cnt;
  return cnt;
}

/* Removes leading characters in TRIM_SET from SS.
   Returns number of characters removed. */
size_t
ss_ltrim (struct substring *ss, struct substring trim_set)
{
  size_t cnt = ss_span (*ss, trim_set);
  ss_advance (ss, cnt);
  return cnt;
}

/* Trims leading and trailing characters in TRIM_SET from SS. */
void
ss_trim (struct substring *ss, struct substring trim_set)
{
  ss_ltrim (ss, trim_set);
  ss_rtrim (ss, trim_set);
}

/* If the last character in SS is C, removes it and returns true.
   Otherwise, returns false without changing the string. */
bool
ss_chomp (struct substring *ss, char c)
{
  if (ss_last (*ss) == c)
    {
      ss->length--;
      return true;
    }
  else
    return false;
}

/* Divides SS into tokens separated by any of the DELIMITERS.
   Each call replaces TOKEN by the next token in SS, or by an
   empty string if no tokens remain.  Returns true if a token was
   obtained, false otherwise.

   Before the first call, initialize *SAVE_IDX to 0.  Do not
   modify *SAVE_IDX between calls.

   SS divides into exactly one more tokens than it contains
   delimiters.  That is, a delimiter at the start or end of SS or
   a pair of adjacent delimiters yields an empty token, and the
   empty string contains a single token. */
bool
ss_separate (struct substring ss, struct substring delimiters,
             size_t *save_idx, struct substring *token)
{
  if (*save_idx <= ss_length (ss))
    {
      struct substring tmp = ss_substr (ss, *save_idx, SIZE_MAX);
      size_t length = ss_cspan (tmp, delimiters);
      *token = ss_head (tmp, length);
      *save_idx += length + 1;
      return true;
    }
  else
    {
      *token = ss_empty ();
      return false;
    }
}

/* Divides SS into tokens separated by any of the DELIMITERS,
   merging adjacent delimiters so that the empty string is never
   produced as a token.  Each call replaces TOKEN by the next
   token in SS, or by an empty string if no tokens remain, and
   then skips past the first delimiter following the token.
   Returns true if a token was obtained, false otherwise.

   Before the first call, initialize *SAVE_IDX to 0.  Do not
   modify *SAVE_IDX between calls. */
bool
ss_tokenize (struct substring ss, struct substring delimiters,
             size_t *save_idx, struct substring *token)
{
  ss_advance (&ss, *save_idx);
  *save_idx += ss_ltrim (&ss, delimiters);
  ss_get_chars (&ss, ss_cspan (ss, delimiters), token);
  *save_idx += ss_length (*token) + 1;
  return ss_length (*token) > 0;
}

/* Removes the first CNT characters from SS. */
void
ss_advance (struct substring *ss, size_t cnt)
{
  if (cnt > ss->length)
    cnt = ss->length;
  ss->string += cnt;
  ss->length -= cnt;
}

/* If the first character in SS is C, removes it and returns true.
   Otherwise, returns false without changing the string. */
bool
ss_match_char (struct substring *ss, char c)
{
  if (ss_first (*ss) == c)
    {
      ss->string++;
      ss->length--;
      return true;
    }
  else
    return false;
}

/* If the first character in SS is in MATCH, removes it and
   returns the character that was removed.
   Otherwise, returns EOF without changing the string. */
int
ss_match_char_in (struct substring *ss, struct substring match)
{
  int c = EOF;
  if (ss->length > 0
      && memchr (match.string, ss->string[0], match.length) != NULL)
    {
      c = ss->string[0];
      ss->string++;
      ss->length--;
    }
  return c;
}

/* If SS begins with TARGET, removes it and returns true.
   Otherwise, returns false without changing SS. */
bool
ss_match_string (struct substring *ss, const struct substring target)
{
  size_t length = ss_length (target);
  if (ss_equals (ss_head (*ss, length), target))
    {
      ss_advance (ss, length);
      return true;
    }
  else
    return false;
}

/* Removes the first character from SS and returns it.
   If SS is empty, returns EOF without modifying SS. */
int
ss_get_char (struct substring *ss)
{
  int c = ss_first (*ss);
  if (c != EOF)
    {
      ss->string++;
      ss->length--;
    }
  return c;
}

/* Stores the prefix of SS up to the first DELIMITER in OUT (if
   any).  Trims those same characters from SS.  DELIMITER is
   removed from SS but not made part of OUT.  Returns true if
   DELIMITER was found (and removed), false otherwise. */
bool
ss_get_until (struct substring *ss, char delimiter, struct substring *out)
{
  ss_get_chars (ss, ss_cspan (*ss, ss_buffer (&delimiter, 1)), out);
  return ss_match_char (ss, delimiter);
}

/* Stores the first CNT characters in SS in OUT (or fewer, if SS
   is shorter than CNT characters).  Trims the same characters
   from the beginning of SS.  Returns CNT. */
size_t
ss_get_chars (struct substring *ss, size_t cnt, struct substring *out)
{
  *out = ss_head (*ss, cnt);
  ss_advance (ss, cnt);
  return cnt;
}

/* Parses and removes an optionally signed decimal integer from
   the beginning of SS.  Returns 0 if an error occurred,
   otherwise the number of characters removed from SS.  Stores
   the integer's value into *VALUE. */
size_t
ss_get_long (struct substring *ss, long *value)
{
  char tmp[64];
  size_t length;

  length = ss_span (*ss, ss_cstr ("+-"));
  length += ss_span (ss_substr (*ss, length, SIZE_MAX), ss_cstr (CC_DIGITS));
  if (length > 0 && length < sizeof tmp)
    {
      char *tail;

      memcpy (tmp, ss_data (*ss), length);
      tmp[length] = '\0';

      *value = strtol (tmp, &tail, 10);
      if (tail - tmp == length)
        {
          ss_advance (ss, length);
          return length;
        }
    }
  *value = 0;
  return 0;
}

/* Returns true if SS is empty (contains no characters),
   false otherwise. */
bool
ss_is_empty (struct substring ss)
{
  return ss.length == 0;
}

/* Returns the number of characters in SS. */
size_t
ss_length (struct substring ss)
{
  return ss.length;
}

/* Returns a pointer to the characters in SS. */
char *
ss_data (struct substring ss)
{
  return ss.string;
}

/* Returns a pointer just past the last character in SS. */
char *
ss_end (struct substring ss)
{
  return ss.string + ss.length;
}

/* Returns the character in position IDX in SS, as a value in the
   range of unsigned char.  Returns EOF if IDX is out of the
   range of indexes for SS. */
int
ss_at (struct substring ss, size_t idx)
{
  return idx < ss.length ? (unsigned char) ss.string[idx] : EOF;
}

/* Returns the first character in SS as a value in the range of
   unsigned char.  Returns EOF if SS is the empty string. */
int
ss_first (struct substring ss)
{
  return ss_at (ss, 0);
}

/* Returns the last character in SS as a value in the range of
   unsigned char.  Returns EOF if SS is the empty string. */
int
ss_last (struct substring ss)
{
  return ss.length > 0 ? (unsigned char) ss.string[ss.length - 1] : EOF;
}

/* Returns the number of contiguous characters at the beginning
   of SS that are in SKIP_SET. */
size_t
ss_span (struct substring ss, struct substring skip_set)
{
  size_t i;
  for (i = 0; i < ss.length; i++)
    if (ss_find_char (skip_set, ss.string[i]) == SIZE_MAX)
      break;
  return i;
}

/* Returns the number of contiguous characters at the beginning
   of SS that are not in SKIP_SET. */
size_t
ss_cspan (struct substring ss, struct substring stop_set)
{
  size_t i;
  for (i = 0; i < ss.length; i++)
    if (ss_find_char (stop_set, ss.string[i]) != SIZE_MAX)
      break;
  return i;
}

/* Returns the offset in SS of the first instance of C,
   or SIZE_MAX if C does not occur in SS. */
size_t
ss_find_char (struct substring ss, char c)
{
  const char *p = memchr (ss.string, c, ss.length);
  return p != NULL ? p - ss.string : SIZE_MAX;
}

/* Compares A and B and returns a strcmp()-type comparison
   result. */
int
ss_compare (struct substring a, struct substring b)
{
  int retval = memcmp (a.string, b.string, MIN (a.length, b.length));
  if (retval == 0)
    retval = a.length < b.length ? -1 : a.length > b.length;
  return retval;
}

/* Compares A and B case-insensitively and returns a
   strcmp()-type comparison result. */
int
ss_compare_case (struct substring a, struct substring b)
{
  int retval = memcasecmp (a.string, b.string, MIN (a.length, b.length));
  if (retval == 0)
    retval = a.length < b.length ? -1 : a.length > b.length;
  return retval;
}

/* Compares A and B and returns true if their contents are
   identical, false otherwise. */
int
ss_equals (struct substring a, struct substring b)
{
  return a.length == b.length && !memcmp (a.string, b.string, a.length);
}

/* Compares A and B and returns true if their contents are
   identical except possibly for case differences, false
   otherwise. */
int
ss_equals_case (struct substring a, struct substring b)
{
  return a.length == b.length && !memcasecmp (a.string, b.string, a.length);
}

/* Returns the position in SS that the character at P occupies.
   P must point within SS or one past its end. */
size_t
ss_pointer_to_position (struct substring ss, const char *p)
{
  size_t pos = p - ss.string;
  assert (pos <= ss.length);
  return pos;
}

/* Allocates and returns a null-terminated string that contains
   SS. */
char *
ss_xstrdup (struct substring ss)
{
  char *s = xmalloc (ss.length + 1);
  memcpy (s, ss.string, ss.length);
  s[ss.length] = '\0';
  return s;
}
\f
/* Initializes ST as an empty string. */
void
ds_init_empty (struct string *st)
{
  st->ss = ss_empty ();
  st->capacity = 0;
}

/* Initializes ST with initial contents S. */
void
ds_init_string (struct string *st, const struct string *s)
{
  ds_init_substring (st, ds_ss (s));
}

/* Initializes ST with initial contents SS. */
void
ds_init_substring (struct string *st, struct substring ss)
{
  st->capacity = MAX (8, ss.length * 2);
  st->ss.string = xmalloc (st->capacity + 1);
  memcpy (st->ss.string, ss.string, ss.length);
  st->ss.length = ss.length;
}

/* Initializes ST with initial contents S. */
void
ds_init_cstr (struct string *st, const char *s)
{
  ds_init_substring (st, ss_cstr (s));
}

/* Frees ST. */
void
ds_destroy (struct string *st)
{
  if (st != NULL)
    {
      ss_dealloc (&st->ss);
      st->ss.string = NULL;
      st->ss.length = 0;
      st->capacity = 0;
    }
}

/* Swaps the contents of strings A and B. */
void
ds_swap (struct string *a, struct string *b)
{
  struct string tmp = *a;
  *a = *b;
  *b = tmp;
}

/* Helper function for ds_register_pool. */
static void
free_string (void *st_)
{
  struct string *st = st_;
  ds_destroy (st);
}

/* Arranges for ST to be destroyed automatically as part of
   POOL. */
void
ds_register_pool (struct string *st, struct pool *pool)
{
  pool_register (pool, free_string, st);
}

/* Cancels the arrangement for ST to be destroyed automatically
   as part of POOL. */
void
ds_unregister_pool (struct string *st, struct pool *pool)
{
  pool_unregister (pool, st);
}

/* Copies SRC into DST.
   DST and SRC may be the same string. */
void
ds_assign_string (struct string *dst, const struct string *src)
{
  ds_assign_substring (dst, ds_ss (src));
}

/* Replaces DST by SS.
   SS may be a substring of DST. */
void
ds_assign_substring (struct string *dst, struct substring ss)
{
  dst->ss.length = ss.length;
  ds_extend (dst, ss.length);
  memmove (dst->ss.string, ss.string, ss.length);
}

/* Replaces DST by null-terminated string SRC.  SRC may overlap
   with DST. */
void
ds_assign_cstr (struct string *dst, const char *src)
{
  ds_assign_substring (dst, ss_cstr (src));
}

/* Truncates ST to zero length. */
void
ds_clear (struct string *st)
{
  st->ss.length = 0;
}

/* Returns a substring that contains ST. */
struct substring
ds_ss (const struct string *st)
{
  return st->ss;
}

/* Returns a substring that contains CNT characters from ST
   starting at position START.

   If START is greater than or equal to the length of ST, then
   the substring will be the empty string.  If START + CNT
   exceeds the length of ST, then the substring will only be
   ds_length(ST) - START characters long. */
struct substring
ds_substr (const struct string *st, size_t start, size_t cnt)
{
  return ss_substr (ds_ss (st), start, cnt);
}

/* Returns a substring that contains the first CNT characters in
   ST.  If CNT exceeds the length of ST, then the substring will
   contain all of ST. */
struct substring
ds_head (const struct string *st, size_t cnt)
{
  return ss_head (ds_ss (st), cnt);
}

/* Returns a substring that contains the last CNT characters in
   ST.  If CNT exceeds the length of ST, then the substring will
   contain all of ST. */
struct substring
ds_tail (const struct string *st, size_t cnt)
{
  return ss_tail (ds_ss (st), cnt);
}

/* Ensures that ST can hold at least MIN_CAPACITY characters plus a null
   terminator. */
void
ds_extend (struct string *st, size_t min_capacity)
{
  if (min_capacity > st->capacity)
    {
      st->capacity *= 2;
      if (st->capacity < min_capacity)
        st->capacity = 2 * min_capacity;

      st->ss.string = xrealloc (st->ss.string, st->capacity + 1);
    }
}

/* Shrink ST to the minimum capacity need to contain its content. */
void
ds_shrink (struct string *st)
{
  if (st->capacity != st->ss.length)
    {
      st->capacity = st->ss.length;
      st->ss.string = xrealloc (st->ss.string, st->capacity + 1);
    }
}

/* Truncates ST to at most LENGTH characters long. */
void
ds_truncate (struct string *st, size_t length)
{
  ss_truncate (&st->ss, length);
}

/* Removes trailing characters in TRIM_SET from ST.
   Returns number of characters removed. */
size_t
ds_rtrim (struct string *st, struct substring trim_set)
{
  return ss_rtrim (&st->ss, trim_set);
}

/* Removes leading characters in TRIM_SET from ST.
   Returns number of characters removed. */
size_t
ds_ltrim (struct string *st, struct substring trim_set)
{
  size_t cnt = ds_span (st, trim_set);
  if (cnt > 0)
    ds_assign_substring (st, ds_substr (st, cnt, SIZE_MAX));
  return cnt;
}

/* Trims leading and trailing characters in TRIM_SET from ST.
   Returns number of charactesr removed. */
size_t
ds_trim (struct string *st, struct substring trim_set)
{
  size_t cnt = ds_rtrim (st, trim_set);
  return cnt + ds_ltrim (st, trim_set);
}

/* If the last character in ST is C, removes it and returns true.
   Otherwise, returns false without modifying ST. */
bool
ds_chomp (struct string *st, char c)
{
  return ss_chomp (&st->ss, c);
}

/* Divides ST into tokens separated by any of the DELIMITERS.
   Each call replaces TOKEN by the next token in ST, or by an
   empty string if no tokens remain.  Returns true if a token was
   obtained, false otherwise.

   Before the first call, initialize *SAVE_IDX to 0.  Do not
   modify *SAVE_IDX between calls.

   ST divides into exactly one more tokens than it contains
   delimiters.  That is, a delimiter at the start or end of ST or
   a pair of adjacent delimiters yields an empty token, and the
   empty string contains a single token. */
bool
ds_separate (const struct string *st, struct substring delimiters,
             size_t *save_idx, struct substring *token)
{
  return ss_separate (ds_ss (st), delimiters, save_idx, token);
}

/* Divides ST into tokens separated by any of the DELIMITERS,
   merging adjacent delimiters so that the empty string is never
   produced as a token.  Each call replaces TOKEN by the next
   token in ST, or by an empty string if no tokens remain.
   Returns true if a token was obtained, false otherwise.

   Before the first call, initialize *SAVE_IDX to 0.  Do not
   modify *SAVE_IDX between calls. */
bool
ds_tokenize (const struct string *st, struct substring delimiters,
             size_t *save_idx, struct substring *token)
{
  return ss_tokenize (ds_ss (st), delimiters, save_idx, token);
}

/* Pad ST on the right with copies of PAD until ST is at least
   LENGTH characters in size.  If ST is initially LENGTH
   characters or longer, this is a no-op. */
void
ds_rpad (struct string *st, size_t length, char pad)
{
  if (length > st->ss.length)
    ds_put_char_multiple (st, pad, length - st->ss.length);
}

/* Sets the length of ST to exactly NEW_LENGTH,
   either by truncating characters from the end,
   or by padding on the right with PAD. */
void
ds_set_length (struct string *st, size_t new_length, char pad)
{
  if (st->ss.length < new_length)
    ds_rpad (st, new_length, pad);
  else
    st->ss.length = new_length;
}

/* Returns true if ST is empty, false otherwise. */
bool
ds_is_empty (const struct string *st)
{
  return ss_is_empty (st->ss);
}

/* Returns the length of ST. */
size_t
ds_length (const struct string *st)
{
  return ss_length (ds_ss (st));
}

/* Returns the string data inside ST. */
char *
ds_data (const struct string *st)
{
  return ss_data (ds_ss (st));
}

/* Returns a pointer to the null terminator ST.
   This might not be an actual null character unless ds_c_str() has
   been called since the last modification to ST. */
char *
ds_end (const struct string *st)
{
  return ss_end (ds_ss (st));
}

/* Returns the character in position IDX in ST, as a value in the
   range of unsigned char.  Returns EOF if IDX is out of the
   range of indexes for ST. */
int
ds_at (const struct string *st, size_t idx)
{
  return ss_at (ds_ss (st), idx);
}

/* Returns the first character in ST as a value in the range of
   unsigned char.  Returns EOF if ST is the empty string. */
int
ds_first (const struct string *st)
{
  return ss_first (ds_ss (st));
}

/* Returns the last character in ST as a value in the range of
   unsigned char.  Returns EOF if ST is the empty string. */
int
ds_last (const struct string *st)
{
  return ss_last (ds_ss (st));
}

/* Returns the number of consecutive characters at the beginning
   of ST that are in SKIP_SET. */
size_t
ds_span (const struct string *st, struct substring skip_set)
{
  return ss_span (ds_ss (st), skip_set);
}

/* Returns the number of consecutive characters at the beginning
   of ST that are not in STOP_SET.  */
size_t
ds_cspan (const struct string *st, struct substring stop_set)
{
  return ss_cspan (ds_ss (st), stop_set);
}

/* Returns the position of the first occurrence of character C in
   ST at or after position OFS, or SIZE_MAX if there is no such
   occurrence. */
size_t
ds_find_char (const struct string *st, char c)
{
  return ss_find_char (ds_ss (st), c);
}

/* Compares A and B and returns a strcmp()-type comparison
   result. */
int
ds_compare (const struct string *a, const struct string *b)
{
  return ss_compare (ds_ss (a), ds_ss (b));
}

/* Returns the position in ST that the character at P occupies.
   P must point within ST or one past its end. */
size_t
ds_pointer_to_position (const struct string *st, const char *p)
{
  return ss_pointer_to_position (ds_ss (st), p);
}

/* Allocates and returns a null-terminated string that contains
   ST. */
char *
ds_xstrdup (const struct string *st)
{
  return ss_xstrdup (ds_ss (st));
}

/* Returns the allocation size of ST. */
size_t
ds_capacity (const struct string *st)
{
  return st->capacity;
}

/* Returns the value of ST as a null-terminated string. */
char *
ds_cstr (const struct string *st_)
{
  struct string *st = (struct string *) st_;
  if (st->ss.string == NULL)
    ds_extend (st, 1);
  st->ss.string[st->ss.length] = '\0';
  return st->ss.string;
}

/* Appends to ST a newline-terminated line read from STREAM, but
   no more than MAX_LENGTH characters.
   Newline is the last character of ST on return, if encountering
   a newline was the reason for terminating.
   Returns true if at least one character was read from STREAM
   and appended to ST, false if no characters at all were read
   before an I/O error or end of file was encountered (or
   MAX_LENGTH was 0). */
bool
ds_read_line (struct string *st, FILE *stream, size_t max_length)
{
  if (!st->ss.length && max_length == SIZE_MAX)
    {
      size_t capacity = st->capacity ? st->capacity + 1 : 0;
      ssize_t n = getline (&st->ss.string, &capacity, stream);
      if (capacity)
        st->capacity = capacity - 1;
      if (n > 0)
        {
          st->ss.length = n;
          return true;
        }
      else
        return false;
    }
  else
    {
      size_t length;

      for (length = 0; length < max_length; length++)
        {
          int c = getc (stream);
          if (c == EOF)
            break;

          ds_put_char (st, c);
          if (c == '\n')
            return true;
        }

      return length > 0;
    }
}

/* Removes a comment introduced by `#' from ST,
   ignoring occurrences inside quoted strings. */
static void
remove_comment (struct string *st)
{
  char *cp;
  int quote = 0;

  for (cp = ds_data (st); cp < ds_end (st); cp++)
    if (quote)
      {
        if (*cp == quote)
          quote = 0;
        else if (*cp == '\\')
          cp++;
      }
    else if (*cp == '\'' || *cp == '"')
      quote = *cp;
    else if (*cp == '#')
      {
        ds_truncate (st, cp - ds_cstr (st));
        break;
      }
}

/* Reads a line from STREAM into ST, then preprocesses as follows:

   - Splices lines terminated with `\'.

   - Deletes comments introduced by `#' outside of single or double
     quotes.

   - Deletes trailing white space.

   Returns true if a line was successfully read, false on
   failure.  If LINE_NUMBER is non-null, then *LINE_NUMBER is
   incremented by the number of lines read. */
bool
ds_read_config_line (struct string *st, int *line_number, FILE *stream)
{
  ds_clear (st);
  do
    {
      if (!ds_read_line (st, stream, SIZE_MAX))
        return false;
      (*line_number)++;
      ds_rtrim (st, ss_cstr (CC_SPACES));
    }
  while (ds_chomp (st, '\\'));

  remove_comment (st);
  return true;
}

/* Attempts to read SIZE * CNT bytes from STREAM and append them
   to ST.
   Returns true if all the requested data was read, false otherwise. */
bool
ds_read_stream (struct string *st, size_t size, size_t cnt, FILE *stream)
{
  if (size != 0)
    {
      size_t try_bytes = xtimes (cnt, size);
      if (size_in_bounds_p (xsum (ds_length (st), try_bytes)))
        {
          char *buffer = ds_put_uninit (st, try_bytes);
          size_t got_bytes = fread (buffer, 1, try_bytes, stream);
          ds_truncate (st, ds_length (st) - (try_bytes - got_bytes));
          return got_bytes == try_bytes;
        }
      else
        {
          errno = ENOMEM;
          return false;
        }
    }
  else
    return true;
}

/* Concatenates S onto ST. */
void
ds_put_cstr (struct string *st, const char *s)
{
  if (s != NULL)
    ds_put_substring (st, ss_cstr (s));
}

/* Concatenates SS to ST. */
void
ds_put_substring (struct string *st, struct substring ss)
{
  memcpy (ds_put_uninit (st, ss_length (ss)), ss_data (ss), ss_length (ss));
}

/* Returns ds_end(ST) and THEN increases the length by INCR. */
char *
ds_put_uninit (struct string *st, size_t incr)
{
  char *end;
  ds_extend (st, ds_length (st) + incr);
  end = ds_end (st);
  st->ss.length += incr;
  return end;
}

/* Formats FORMAT as a printf string and appends the result to ST. */
void
ds_put_format (struct string *st, const char *format, ...)
{
  va_list args;

  va_start (args, format);
  ds_put_vformat (st, format, args);
  va_end (args);
}

/* Formats FORMAT as a printf string and appends the result to ST. */
void
ds_put_vformat (struct string *st, const char *format, va_list args_)
{
  int avail, needed;
  va_list args;

  va_copy (args, args_);
  avail = st->ss.string != NULL ? st->capacity - st->ss.length + 1 : 0;
  needed = vsnprintf (st->ss.string + st->ss.length, avail, format, args);
  va_end (args);

  if (needed >= avail)
    {
      va_copy (args, args_);
      vsprintf (ds_put_uninit (st, needed), format, args);
      va_end (args);
    }
  else
    {
      /* Some old libc's returned -1 when the destination string
         was too short. */
      while (needed == -1)
        {
          ds_extend (st, (st->capacity + 1) * 2);
          avail = st->capacity - st->ss.length + 1;

          va_copy (args, args_);
          needed = vsnprintf (ds_end (st), avail, format, args);
          va_end (args);
        }
      st->ss.length += needed;
    }
}

/* Appends character CH to ST. */
void
ds_put_char (struct string *st, int ch)
{
  ds_put_uninit (st, 1)[0] = ch;
}

/* Appends CNT copies of character CH to ST. */
void
ds_put_char_multiple (struct string *st, int ch, size_t cnt)
{
  memset (ds_put_uninit (st, cnt), ch, cnt);
}