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<title>Integer Special Functions (GNU MP 6.1.0)</title>
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<a name="Integer-Special-Functions"></a>
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<p>
Previous: <a href="Miscellaneous-Integer-Functions.html#Miscellaneous-Integer-Functions" accesskey="p" rel="prev">Miscellaneous Integer Functions</a>, Up: <a href="Integer-Functions.html#Integer-Functions" accesskey="u" rel="up">Integer Functions</a> [<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
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<hr>
<a name="Special-Functions"></a>
<h3 class="section">5.16 Special Functions</h3>
<a name="index-Special-integer-functions"></a>
<a name="index-Integer-special-functions"></a>
<p>The functions in this section are for various special purposes. Most
applications will not need them.
</p>
<dl>
<dt><a name="index-mpz_005farray_005finit"></a>Function: <em>void</em> <strong>mpz_array_init</strong> <em>(mpz_t <var>integer_array</var>, mp_size_t <var>array_size</var>, <span class="nolinebreak">mp_size_t</span> <var><span class="nolinebreak">fixed_num_bits</span></var><!-- /@w -->)</em></dt>
<dd><p><strong>This is an obsolete function. Do not use it.</strong>
</p></dd></dl>
<dl>
<dt><a name="index-_005fmpz_005frealloc"></a>Function: <em>void *</em> <strong>_mpz_realloc</strong> <em>(mpz_t <var>integer</var>, mp_size_t <var>new_alloc</var>)</em></dt>
<dd><p>Change the space for <var>integer</var> to <var>new_alloc</var> limbs. The value in
<var>integer</var> is preserved if it fits, or is set to 0 if not. The return
value is not useful to applications and should be ignored.
</p>
<p><code>mpz_realloc2</code> is the preferred way to accomplish allocation changes like
this. <code>mpz_realloc2</code> and <code>_mpz_realloc</code> are the same except that
<code>_mpz_realloc</code> takes its size in limbs.
</p></dd></dl>
<dl>
<dt><a name="index-mpz_005fgetlimbn"></a>Function: <em>mp_limb_t</em> <strong>mpz_getlimbn</strong> <em>(const mpz_t <var>op</var>, mp_size_t <var>n</var>)</em></dt>
<dd><p>Return limb number <var>n</var> from <var>op</var>. The sign of <var>op</var> is ignored,
just the absolute value is used. The least significant limb is number 0.
</p>
<p><code>mpz_size</code> can be used to find how many limbs make up <var>op</var>.
<code>mpz_getlimbn</code> returns zero if <var>n</var> is outside the range 0 to
<code>mpz_size(<var>op</var>)-1</code>.
</p></dd></dl>
<dl>
<dt><a name="index-mpz_005fsize"></a>Function: <em>size_t</em> <strong>mpz_size</strong> <em>(const mpz_t <var>op</var>)</em></dt>
<dd><p>Return the size of <var>op</var> measured in number of limbs. If <var>op</var> is zero,
the returned value will be zero.
</p></dd></dl>
<dl>
<dt><a name="index-mpz_005flimbs_005fread"></a>Function: <em>const mp_limb_t *</em> <strong>mpz_limbs_read</strong> <em>(const mpz_t <var>x</var>)</em></dt>
<dd><p>Return a pointer to the limb array representing the absolute value of <var>x</var>.
The size of the array is <code>mpz_size(<var>x</var>)</code>. Intended for read access
only.
</p></dd></dl>
<dl>
<dt><a name="index-mpz_005flimbs_005fwrite"></a>Function: <em>mp_limb_t *</em> <strong>mpz_limbs_write</strong> <em>(mpz_t <var>x</var>, mp_size_t <var>n</var>)</em></dt>
<dt><a name="index-mpz_005flimbs_005fmodify"></a>Function: <em>mp_limb_t *</em> <strong>mpz_limbs_modify</strong> <em>(mpz_t <var>x</var>, mp_size_t <var>n</var>)</em></dt>
<dd><p>Return a pointer to the limb array, intended for write access. The array is
reallocated as needed, to make room for <var>n</var> limbs. Requires <em><var>n</var>
> 0</em>. The <code>mpz_limbs_modify</code> function returns an array that holds the old
absolute value of <var>x</var>, while <code>mpz_limbs_write</code> may destroy the old
value and return an array with unspecified contents.
</p></dd></dl>
<dl>
<dt><a name="index-mpz_005flimbs_005ffinish"></a>Function: <em>void</em> <strong>mpz_limbs_finish</strong> <em>(mpz_t <var>x</var>, mp_size_t <var>s</var>)</em></dt>
<dd><p>Updates the internal size field of <var>x</var>. Used after writing to the limb
array pointer returned by <code>mpz_limbs_write</code> or <code>mpz_limbs_modify</code> is
completed. The array should contain <em>abs(<var>s</var>)</em> valid limbs,
representing the new absolute value for <var>x</var>, and the sign of <var>x</var> is
taken from the sign of <var>s</var>. This function never reallocates <var>x</var>, so
the limb pointer remains valid.
</p></dd></dl>
<div class="example">
<pre class="example">void foo (mpz_t x)
{
mp_size_t n, i;
mp_limb_t *xp;
n = mpz_size (x);
xp = mpz_limbs_modify (x, 2*n);
for (i = 0; i < n; i++)
xp[n+i] = xp[n-1-i];
mpz_limbs_finish (x, mpz_sgn (x) < 0 ? - 2*n : 2*n);
}
</pre></div>
<dl>
<dt><a name="index-mpz_005froinit_005fn"></a>Function: <em>mpz_srcptr</em> <strong>mpz_roinit_n</strong> <em>(mpz_t <var>x</var>, const mp_limb_t *<var>xp</var>, mp_size_t <var>xs</var>)</em></dt>
<dd><p>Special initialization of <var>x</var>, using the given limb array and size.
<var>x</var> should be treated as read-only: it can be passed safely as input to
any mpz function, but not as an output. The array <var>xp</var> must point to at
least a readable limb, its size is
<em>abs(<var>xs</var>)</em>, and the sign of <var>x</var> is the sign of <var>xs</var>. For
convenience, the function returns <var>x</var>, but cast to a const pointer type.
</p></dd></dl>
<div class="example">
<pre class="example">void foo (mpz_t x)
{
static const mp_limb_t y[3] = { 0x1, 0x2, 0x3 };
mpz_t tmp;
mpz_add (x, x, mpz_roinit_n (tmp, y, 3));
}
</pre></div>
<dl>
<dt><a name="index-MPZ_005fROINIT_005fN"></a>Macro: <em>mpz_t</em> <strong>MPZ_ROINIT_N</strong> <em>(mp_limb_t *<var>xp</var>, mp_size_t <var>xs</var>)</em></dt>
<dd><p>This macro expands to an initializer which can be assigned to an mpz_t
variable. The limb array <var>xp</var> must point to at least a readable limb,
moreover, unlike the <code>mpz_roinit_n</code> function, the array must be
normalized: if <var>xs</var> is non-zero, then
<code><var>xp</var>[<em>abs(<var>xs</var>)-1</em>]</code> must be non-zero. Intended
primarily for constant values. Using it for non-constant values requires a C
compiler supporting C99.
</p></dd></dl>
<div class="example">
<pre class="example">void foo (mpz_t x)
{
static const mp_limb_t ya[3] = { 0x1, 0x2, 0x3 };
static const mpz_t y = MPZ_ROINIT_N ((mp_limb_t *) ya, 3);
mpz_add (x, x, y);
}
</pre></div>
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