key-gen.c   [plain text]

/* key-gen.c --- manufacturing sequential keys for some db tables
 *
 * ====================================================================
 * Copyright (c) 2000-2004 CollabNet.  All rights reserved.
 *
 * This software is licensed as described in the file COPYING, which
 * you should have received as part of this distribution.  The terms
 * are also available at http://subversion.tigris.org/license-1.html.
 * If newer versions of this license are posted there, you may use a
 * newer version instead, at your option.
 *
 * This software consists of voluntary contributions made by many
 * individuals.  For exact contribution history, see the revision
 * history and logs, available at http://subversion.tigris.org/.
 * ====================================================================
 */

#include <assert.h>
#include <string.h>

#define APR_WANT_STRFUNC
#include <apr_want.h>
#include <stdlib.h>
#include <apr.h>
#include "key-gen.h"


/* Converting text to numbers.  */

apr_size_t
svn_fs_base__getsize(const char *data, apr_size_t len,
                     const char **endptr, apr_size_t max)
{
  /* We can't detect overflow by simply comparing value against max,
     since multiplying value by ten can overflow in strange ways if
     max is close to the limits of apr_size_t.  For example, suppose
     that max is 54, and apr_size_t is six bits long; its range is
     0..63.  If we're parsing the number "502", then value will be 50
     after parsing the first two digits.  50 * 10 = 500.  But 500
     doesn't fit in an apr_size_t, so it'll be truncated to 500 mod 64
     = 52, which is less than max, so we'd fail to recognize the
     overflow.  Furthermore, it *is* greater than 50, so you can't
     detect overflow by checking whether value actually increased
     after each multiplication --- sometimes it does increase, but
     it's still wrong.

     So we do the check for overflow before we multiply value and add
     in the new digit.  */
  apr_size_t max_prefix = max / 10;
  apr_size_t max_digit = max % 10;
  apr_size_t i;
  apr_size_t value = 0;

  for (i = 0; i < len && '0' <= data[i] && data[i] <= '9'; i++)
    {
      apr_size_t digit = data[i] - '0';

      /* Check for overflow.  */
      if (value > max_prefix
          || (value == max_prefix && digit > max_digit))
        {
          *endptr = 0;
          return 0;
        }

      value = (value * 10) + digit;
    }

  /* There must be at least one digit there.  */
  if (i == 0)
    {
      *endptr = 0;
      return 0;
    }
  else
    {
      *endptr = data + i;
      return value;
    }
}



/* Converting numbers to text.  */

int
svn_fs_base__putsize(char *data, apr_size_t len, apr_size_t value)
{
  apr_size_t i = 0;

  /* Generate the digits, least-significant first.  */
  do
    {
      if (i >= len)
        return 0;

      data[i] = (value % 10) + '0';
      value /= 10;
      i++;
    }
  while (value > 0);

  /* Put the digits in most-significant-first order.  */
  {
    int left, right;

    for (left = 0, right = i-1; left < right; left++, right--)
      {
        char t = data[left];
        data[left] = data[right];
        data[right] = t;
      }
  }

  return i;
}



/*** Keys for reps and strings. ***/


void
svn_fs_base__next_key(const char *this, apr_size_t *len, char *next)
{
  apr_size_t olen = *len;     /* remember the first length */
  int i = olen - 1;           /* initial index; we work backwards */
  char c;                     /* current char */
  svn_boolean_t carry = TRUE; /* boolean: do we have a carry or not?
                                 We start with a carry, because we're
                                 incrementing the number, after all. */

  /* Leading zeros are not allowed, except for the string "0". */
  if ((*len > 1) && (this[0] == '0'))
    {
      *len = 0;
      return;
    }

  for (i = (olen - 1); i >= 0; i--)
    {
      c = this[i];

      /* Validate as we go. */
      if (! (((c >= '0') && (c <= '9')) || ((c >= 'a') && (c <= 'z'))))
        {
          *len = 0;
          return;
        }

      if (carry)
        {
          if (c == 'z')
            next[i] = '0';
          else
            {
              carry = FALSE;

              if (c == '9')
                next[i] = 'a';
              else
                next[i] = c + 1;
            }
        }
      else
        next[i] = c;
    }

  /* The new length is OLEN, plus 1 if there's a carry out of the
     leftmost digit. */
  *len = olen + (carry ? 1 : 0);

  /* Ensure that we haven't overrun the (ludicrous) bound on key length.
     Note that MAX_KEY_SIZE is a bound on the size *including*
     the trailing null byte. */
  assert(*len < MAX_KEY_SIZE);

  /* Now we know it's safe to add the null terminator. */
  next[*len] = '\0';

  /* Handle any leftover carry. */
  if (carry)
    {
      memmove(next+1, next, olen);
      next[0] = '1';
    }
}


int
svn_fs_base__key_compare(const char *a, const char *b)
{
  int a_len = strlen(a);
  int b_len = strlen(b);
  int cmp;

  if (a_len > b_len)
    return 1;
  if (b_len > a_len)
    return -1;
  cmp = strcmp(a, b);
  return (cmp ? (cmp / abs(cmp)) : 0);
}


svn_boolean_t
svn_fs_base__same_keys(const char *a, const char *b)
{
  if (! (a || b))
    return TRUE;
  if (a && (! b))
    return FALSE;
  if ((! a) && b)
    return FALSE;
  return (strcmp(a, b) == 0) ? TRUE : FALSE;
}