<parameter>iter_count</parameter>
    parameter is omitted, the default iteration count is used.
    Allowed values for <parameter>iter_count</parameter> depend on the algorithm and
    are shown in <xref linkend="pgcrypto-icfc-table"/>.
   </para>

   <table id="pgcrypto-icfc-table">
    <title>Iteration Counts for <function>crypt()</function></title>
    <tgroup cols="4">
     <thead>
      <row>
       <entry>Algorithm</entry>
       <entry>Default</entry>
       <entry>Min</entry>
       <entry>Max</entry>
      </row>
     </thead>
     <tbody>
      <row>
       <entry><literal>xdes</literal></entry>
       <entry>725</entry>
       <entry>1</entry>
       <entry>16777215</entry>
      </row>
      <row>
       <entry><literal>bf</literal></entry>
       <entry>6</entry>
       <entry>4</entry>
       <entry>31</entry>
      </row>
      <row>
       <entry><literal>sha256crypt, sha512crypt</literal></entry>
       <entry>5000</entry>
       <entry>1000</entry>
       <entry>999999999</entry>
      </row>
     </tbody>
    </tgroup>
   </table>

   <para>
    For <literal>xdes</literal> there is an additional limitation that the
    iteration count must be an odd number.
   </para>

   <para>
    To pick an appropriate iteration count, consider that
    the original DES crypt was designed to have the speed of 4 hashes per
    second on the hardware of that time.
    Slower than 4 hashes per second would probably dampen usability.
    Faster than 100 hashes per second is probably too fast.
   </para>

   <para>
    <xref linkend="pgcrypto-hash-speed-table"/> gives an overview of the relative slowness
    of different hashing algorithms.
    The table shows how much time it would take to try all
    combinations of characters in an 8-character password, assuming
    that the password contains either only lower case letters, or
    upper- and lower-case letters and numbers.
    In the <literal>crypt-bf</literal> entries, the number after a slash is
    the <parameter>iter_count</parameter> parameter of
    <function>gen_salt</function>.
   </para>

   <para>
   The default <parameter>iter_count</parameter> for <literal>sha256crypt</literal> and
   <literal>sha512crypt</literal> of <literal>5000</literal> is considered too low for modern
   hardware, but can be adjusted to generate stronger password hashes.
   Otherwise both hashes, <literal>sha256crypt</literal> and <literal>sha512crypt</literal> are
   considered safe.
   </para>

   <table id="pgcrypto-hash-speed-table">
    <title>Hash Algorithm Speeds</title>
    <tgroup cols="5">
     <thead>
      <row>
       <entry>Algorithm</entry>
       <entry>Hashes/sec</entry>
       <entry>For <literal>[a-z]</literal></entry>
       <entry>For <literal>[A-Za-z0-9]</literal></entry>
       <entry>Duration relative to <literal>md5 hash</literal></entry>
      </row>
     </thead>
     <tbody>
      <row>
       <entry><literal>crypt-bf/8</literal></entry>
       <entry>1792</entry>
       <entry>4 years</entry>
       <entry>3927 years</entry>
       <entry>100k</entry>
      </row>
      <row>
       <entry><literal>crypt-bf/7</literal></entry>
       <entry>3648</entry>
       <entry>2 years</entry>
       <entry>1929 years</entry>
       <entry>50k</entry>
      </row>
      <row>
       <entry><literal>crypt-bf/6</literal></entry>
       <entry>7168</entry>
       <entry>1 year</entry>
       <entry>982 years</entry>
       <entry>25k</entry>
      </row>
      <row>
       <entry><literal>crypt-bf/5</literal></entry>
       <entry>13504</entry>
       <entry>188 days</entry>
       <entry>521 years</entry>
       <entry>12.5k</entry>
      </row>
      <row>
       <entry><literal>crypt-md5</literal></entry>
       <entry>171584</entry>
       <entry>15 days</entry>
       <entry>41 years</entry>
       <entry>1k</entry>
      </row>
      <row>
       <entry><literal>crypt-des</literal></entry>
       <entry>23221568</entry>
       <entry>157.5 minutes</entry>
       <entry>108