xref: /netbsd-src/external/lgpl3/mpfr/dist/src/gmp_op.c (revision ba125506a622fe649968631a56eba5d42ff57863)
1 /* Implementations of operations between mpfr and mpz/mpq data
2 
3 Copyright 2001, 2003-2023 Free Software Foundation, Inc.
4 Contributed by the AriC and Caramba projects, INRIA.
5 
6 This file is part of the GNU MPFR Library.
7 
8 The GNU MPFR Library is free software; you can redistribute it and/or modify
9 it under the terms of the GNU Lesser General Public License as published by
10 the Free Software Foundation; either version 3 of the License, or (at your
11 option) any later version.
12 
13 The GNU MPFR Library is distributed in the hope that it will be useful, but
14 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
15 or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
16 License for more details.
17 
18 You should have received a copy of the GNU Lesser General Public License
19 along with the GNU MPFR Library; see the file COPYING.LESSER.  If not, see
20 https://www.gnu.org/licenses/ or write to the Free Software Foundation, Inc.,
21 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA. */
22 
23 #define MPFR_NEED_LONGLONG_H
24 #include "mpfr-impl.h"
25 
26 /* TODO: for functions with mpz_srcptr, check whether mpz_fits_slong_p
27    is really useful in all cases. For instance, concerning the addition,
28    one now has mpz_t -> long -> unsigned long -> mpfr_t then mpfr_add
29    instead of mpz_t -> mpfr_t then mpfr_add. */
30 
31 /* Init and set a mpfr_t with enough precision to store a mpz.
32    This function should be called in the extended exponent range. */
33 static void
init_set_z(mpfr_ptr t,mpz_srcptr z)34 init_set_z (mpfr_ptr t, mpz_srcptr z)
35 {
36   mpfr_prec_t p;
37   int i;
38 
39   if (mpz_size (z) <= 1)
40     p = GMP_NUMB_BITS;
41   else
42     MPFR_MPZ_SIZEINBASE2 (p, z);
43   mpfr_init2 (t, p);
44   i = mpfr_set_z (t, z, MPFR_RNDN);
45   /* Possible assertion failure in case of overflow. Such cases,
46      which imply that z is huge (if the function is called in
47      the extended exponent range), are currently not supported,
48      just like precisions around MPFR_PREC_MAX. */
49   MPFR_ASSERTN (i == 0);  (void) i; /* use i to avoid a warning */
50 }
51 
52 /* Init, set a mpfr_t with enough precision to store a mpz_t without round,
53    call the function, and clear the allocated mpfr_t  */
54 static int
foo(mpfr_ptr x,mpfr_srcptr y,mpz_srcptr z,mpfr_rnd_t r,int (* f)(mpfr_ptr,mpfr_srcptr,mpfr_srcptr,mpfr_rnd_t))55 foo (mpfr_ptr x, mpfr_srcptr y, mpz_srcptr z, mpfr_rnd_t r,
56      int (*f)(mpfr_ptr, mpfr_srcptr, mpfr_srcptr, mpfr_rnd_t))
57 {
58   mpfr_t t;
59   int i;
60   MPFR_SAVE_EXPO_DECL (expo);
61 
62   MPFR_SAVE_EXPO_MARK (expo);
63   init_set_z (t, z);  /* There should be no exceptions. */
64   i = (*f) (x, y, t, r);
65   MPFR_SAVE_EXPO_UPDATE_FLAGS (expo, __gmpfr_flags);
66   mpfr_clear (t);
67   MPFR_SAVE_EXPO_FREE (expo);
68   return mpfr_check_range (x, i, r);
69 }
70 
71 static int
foo2(mpfr_ptr x,mpz_srcptr y,mpfr_srcptr z,mpfr_rnd_t r,int (* f)(mpfr_ptr,mpfr_srcptr,mpfr_srcptr,mpfr_rnd_t))72 foo2 (mpfr_ptr x, mpz_srcptr y, mpfr_srcptr z, mpfr_rnd_t r,
73      int (*f)(mpfr_ptr, mpfr_srcptr, mpfr_srcptr, mpfr_rnd_t))
74 {
75   mpfr_t t;
76   int i;
77   MPFR_SAVE_EXPO_DECL (expo);
78 
79   MPFR_SAVE_EXPO_MARK (expo);
80   init_set_z (t, y);  /* There should be no exceptions. */
81   i = (*f) (x, t, z, r);
82   MPFR_SAVE_EXPO_UPDATE_FLAGS (expo, __gmpfr_flags);
83   mpfr_clear (t);
84   MPFR_SAVE_EXPO_FREE (expo);
85   return mpfr_check_range (x, i, r);
86 }
87 
88 int
mpfr_mul_z(mpfr_ptr y,mpfr_srcptr x,mpz_srcptr z,mpfr_rnd_t r)89 mpfr_mul_z (mpfr_ptr y, mpfr_srcptr x, mpz_srcptr z, mpfr_rnd_t r)
90 {
91   if (mpz_fits_slong_p (z))
92     return mpfr_mul_si (y, x, mpz_get_si (z), r);
93   else
94     return foo (y, x, z, r, mpfr_mul);
95 }
96 
97 int
mpfr_div_z(mpfr_ptr y,mpfr_srcptr x,mpz_srcptr z,mpfr_rnd_t r)98 mpfr_div_z (mpfr_ptr y, mpfr_srcptr x, mpz_srcptr z, mpfr_rnd_t r)
99 {
100   if (mpz_fits_slong_p (z))
101     return mpfr_div_si (y, x, mpz_get_si (z), r);
102   else
103     return foo (y, x, z, r, mpfr_div);
104 }
105 
106 int
mpfr_add_z(mpfr_ptr y,mpfr_srcptr x,mpz_srcptr z,mpfr_rnd_t r)107 mpfr_add_z (mpfr_ptr y, mpfr_srcptr x, mpz_srcptr z, mpfr_rnd_t r)
108 {
109   if (mpz_fits_slong_p (z))
110     return mpfr_add_si (y, x, mpz_get_si (z), r);
111   else
112     return foo (y, x, z, r, mpfr_add);
113 }
114 
115 int
mpfr_sub_z(mpfr_ptr y,mpfr_srcptr x,mpz_srcptr z,mpfr_rnd_t r)116 mpfr_sub_z (mpfr_ptr y, mpfr_srcptr x, mpz_srcptr z, mpfr_rnd_t r)
117 {
118   if (mpz_fits_slong_p (z))
119     return mpfr_sub_si (y, x, mpz_get_si (z), r);
120   else
121     return foo (y, x, z, r, mpfr_sub);
122 }
123 
124 int
mpfr_z_sub(mpfr_ptr y,mpz_srcptr x,mpfr_srcptr z,mpfr_rnd_t r)125 mpfr_z_sub (mpfr_ptr y, mpz_srcptr x, mpfr_srcptr z, mpfr_rnd_t r)
126 {
127   if (mpz_fits_slong_p (x))
128     return mpfr_si_sub (y, mpz_get_si (x), z, r);
129   else
130     return foo2 (y, x, z, r, mpfr_sub);
131 }
132 
133 int
mpfr_cmp_z(mpfr_srcptr x,mpz_srcptr z)134 mpfr_cmp_z (mpfr_srcptr x, mpz_srcptr z)
135 {
136   mpfr_t t;
137   int res;
138   mpfr_prec_t p;
139   mpfr_flags_t flags;
140 
141   if (MPFR_UNLIKELY (MPFR_IS_SINGULAR (x)))
142     return mpfr_cmp_si (x, mpz_sgn (z));
143 
144   if (mpz_fits_slong_p (z))
145     return mpfr_cmp_si (x, mpz_get_si (z));
146 
147   if (mpz_size (z) <= 1)
148     p = GMP_NUMB_BITS;
149   else
150     MPFR_MPZ_SIZEINBASE2 (p, z);
151   mpfr_init2 (t, p);
152   flags = __gmpfr_flags;
153   if (mpfr_set_z (t, z, MPFR_RNDN))
154     {
155       /* overflow (t is an infinity) or underflow: z does not fit in the
156          current exponent range.
157          If overflow, then z is larger than the largest *integer* < +Inf
158          (if z > 0), thus we get t = +Inf (or -Inf), and the value of
159          mpfr_cmp (x, t) below is correct.
160          If underflow, then z is smaller than the smallest number > 0,
161          which is necessarily an integer, say xmin.
162          If z > xmin/2, then t is xmin, and we divide t by 2 to ensure t
163          is zero, and then the value of mpfr_cmp (x, t) below is correct. */
164       mpfr_div_2ui (t, t, 2, MPFR_RNDZ);  /* if underflow, set t to zero */
165       __gmpfr_flags = flags;  /* restore the flags */
166       /* The real value of t (= z), which falls outside the exponent range,
167          has been replaced by an equivalent value for the comparison: zero
168          or an infinity. */
169     }
170   res = mpfr_cmp (x, t);
171   mpfr_clear (t);
172   return res;
173 }
174 
175 #ifndef MPFR_USE_MINI_GMP
176 /* Compute y = RND(x*n/d), where n and d are mpz integers.
177    An integer 0 is assumed to have a positive sign.
178    This function is used by mpfr_mul_q and mpfr_div_q.
179    Note: the status of the rational 0/(-1) is not clear (if there is
180    a signed infinity, there should be a signed zero). But infinities
181    are not currently supported/documented in GMP, and if the rational
182    is canonicalized as it should be, the case 0/(-1) cannot occur. */
183 static int
mpfr_muldiv_z(mpfr_ptr y,mpfr_srcptr x,mpz_srcptr n,mpz_srcptr d,mpfr_rnd_t rnd_mode)184 mpfr_muldiv_z (mpfr_ptr y, mpfr_srcptr x, mpz_srcptr n, mpz_srcptr d,
185                mpfr_rnd_t rnd_mode)
186 {
187   if (MPFR_UNLIKELY (mpz_sgn (n) == 0))
188     {
189       if (MPFR_UNLIKELY (mpz_sgn (d) == 0))
190         MPFR_SET_NAN (y);
191       else
192         {
193           mpfr_mul_ui (y, x, 0, MPFR_RNDN);  /* exact: +0, -0 or NaN */
194           if (MPFR_UNLIKELY (mpz_sgn (d) < 0))
195             MPFR_CHANGE_SIGN (y);
196         }
197       return 0;
198     }
199   else if (MPFR_UNLIKELY (mpz_sgn (d) == 0))
200     {
201       mpfr_div_ui (y, x, 0, MPFR_RNDN);  /* exact: +Inf, -Inf or NaN */
202       if (MPFR_UNLIKELY (mpz_sgn (n) < 0))
203         MPFR_CHANGE_SIGN (y);
204       return 0;
205     }
206   else
207     {
208       mpfr_prec_t p;
209       mpfr_t tmp;
210       int inexact;
211       MPFR_SAVE_EXPO_DECL (expo);
212 
213       MPFR_SAVE_EXPO_MARK (expo);
214 
215       /* With the current MPFR code, using mpfr_mul_z and mpfr_div_z
216          for the general case should be faster than doing everything
217          in mpn, mpz and/or mpq. MPFR_SAVE_EXPO_MARK could be avoided
218          here, but it would be more difficult to handle corner cases. */
219       MPFR_MPZ_SIZEINBASE2 (p, n);
220       mpfr_init2 (tmp, MPFR_PREC (x) + p);
221       inexact = mpfr_mul_z (tmp, x, n, MPFR_RNDN);
222       /* Since |n| >= 1, an underflow is not possible. And the precision of
223          tmp has been chosen so that inexact != 0 iff there's an overflow. */
224       if (MPFR_UNLIKELY (inexact != 0))
225         {
226           mpfr_t x0;
227           mpfr_exp_t ex;
228           MPFR_BLOCK_DECL (flags);
229 
230           /* intermediate overflow case */
231           MPFR_ASSERTD (mpfr_inf_p (tmp));
232           ex = MPFR_GET_EXP (x);  /* x is a pure FP number */
233           MPFR_ALIAS (x0, x, MPFR_SIGN(x), 0);  /* x0 = x / 2^ex */
234           MPFR_BLOCK (flags,
235                       inexact = mpfr_mul_z (tmp, x0, n, MPFR_RNDN);
236                       MPFR_ASSERTD (inexact == 0);
237                       inexact = mpfr_div_z (y, tmp, d, rnd_mode);
238                       /* Just in case the division underflows
239                          (highly unlikely, not supported)... */
240                       MPFR_ASSERTN (!MPFR_BLOCK_EXCEP));
241           MPFR_EXP (y) += ex;
242           /* Detect highly unlikely, not supported corner cases... */
243           MPFR_ASSERTN (MPFR_EXP (y) >= __gmpfr_emin);
244           MPFR_ASSERTN (! MPFR_IS_SINGULAR (y));
245           /* The potential overflow will be detected by mpfr_check_range. */
246         }
247       else
248         inexact = mpfr_div_z (y, tmp, d, rnd_mode);
249 
250       mpfr_clear (tmp);
251 
252       MPFR_SAVE_EXPO_FREE (expo);
253       return mpfr_check_range (y, inexact, rnd_mode);
254     }
255 }
256 
257 int
mpfr_mul_q(mpfr_ptr y,mpfr_srcptr x,mpq_srcptr z,mpfr_rnd_t rnd_mode)258 mpfr_mul_q (mpfr_ptr y, mpfr_srcptr x, mpq_srcptr z, mpfr_rnd_t rnd_mode)
259 {
260   return mpfr_muldiv_z (y, x, mpq_numref (z), mpq_denref (z), rnd_mode);
261 }
262 
263 int
mpfr_div_q(mpfr_ptr y,mpfr_srcptr x,mpq_srcptr z,mpfr_rnd_t rnd_mode)264 mpfr_div_q (mpfr_ptr y, mpfr_srcptr x, mpq_srcptr z, mpfr_rnd_t rnd_mode)
265 {
266   return mpfr_muldiv_z (y, x, mpq_denref (z), mpq_numref (z), rnd_mode);
267 }
268 
269 int
mpfr_add_q(mpfr_ptr y,mpfr_srcptr x,mpq_srcptr z,mpfr_rnd_t rnd_mode)270 mpfr_add_q (mpfr_ptr y, mpfr_srcptr x, mpq_srcptr z, mpfr_rnd_t rnd_mode)
271 {
272   mpfr_t      t,q;
273   mpfr_prec_t p;
274   mpfr_exp_t  err;
275   int res;
276   MPFR_SAVE_EXPO_DECL (expo);
277   MPFR_ZIV_DECL (loop);
278 
279   if (MPFR_UNLIKELY (MPFR_IS_SINGULAR (x)))
280     {
281       if (MPFR_IS_NAN (x))
282         {
283           MPFR_SET_NAN (y);
284           MPFR_RET_NAN;
285         }
286       else if (MPFR_IS_INF (x))
287         {
288           if (MPFR_UNLIKELY (mpz_sgn (mpq_denref (z)) == 0 &&
289                              MPFR_MULT_SIGN (mpz_sgn (mpq_numref (z)),
290                                              MPFR_SIGN (x)) <= 0))
291             {
292               MPFR_SET_NAN (y);
293               MPFR_RET_NAN;
294             }
295           MPFR_SET_INF (y);
296           MPFR_SET_SAME_SIGN (y, x);
297           MPFR_RET (0);
298         }
299       else
300         {
301           MPFR_ASSERTD (MPFR_IS_ZERO (x));
302           if (MPFR_UNLIKELY (mpq_sgn (z) == 0))
303             return mpfr_set (y, x, rnd_mode); /* signed 0 - Unsigned 0 */
304           else
305             return mpfr_set_q (y, z, rnd_mode);
306         }
307     }
308 
309   MPFR_SAVE_EXPO_MARK (expo);
310 
311   p = MPFR_PREC (y) + 10;
312   mpfr_init2 (t, p);
313   mpfr_init2 (q, p);
314 
315   MPFR_ZIV_INIT (loop, p);
316   for (;;)
317     {
318       MPFR_BLOCK_DECL (flags);
319 
320       res = mpfr_set_q (q, z, MPFR_RNDN);  /* Error <= 1/2 ulp(q) */
321       /* If z if @INF@ (1/0), res = 0, so it quits immediately */
322       if (MPFR_UNLIKELY (res == 0))
323         /* Result is exact so we can add it directly! */
324         {
325           res = mpfr_add (y, x, q, rnd_mode);
326           break;
327         }
328       MPFR_BLOCK (flags, mpfr_add (t, x, q, MPFR_RNDN));
329       /* Error on t is <= 1/2 ulp(t), except in case of overflow/underflow,
330          but such an exception is very unlikely as it would be possible
331          only if q has a huge numerator or denominator. Not supported! */
332       MPFR_ASSERTN (! (MPFR_OVERFLOW (flags) || MPFR_UNDERFLOW (flags)));
333       /* Error / ulp(t)      <= 1/2 + 1/2 * 2^(EXP(q)-EXP(t))
334          If EXP(q)-EXP(t)>0, <= 2^(EXP(q)-EXP(t)-1)*(1+2^-(EXP(q)-EXP(t)))
335                              <= 2^(EXP(q)-EXP(t))
336          If EXP(q)-EXP(t)<0, <= 2^0 */
337       /* We can get 0, but we can't round since q is inexact */
338       if (MPFR_LIKELY (!MPFR_IS_ZERO (t)))
339         {
340           err = (mpfr_exp_t) p - 1 - MAX (MPFR_GET_EXP(q)-MPFR_GET_EXP(t), 0);
341           if (MPFR_LIKELY (MPFR_CAN_ROUND (t, err, MPFR_PREC (y), rnd_mode)))
342             {
343               res = mpfr_set (y, t, rnd_mode);
344               break;
345             }
346         }
347       MPFR_ZIV_NEXT (loop, p);
348       mpfr_set_prec (t, p);
349       mpfr_set_prec (q, p);
350     }
351   MPFR_ZIV_FREE (loop);
352   mpfr_clear (t);
353   mpfr_clear (q);
354 
355   MPFR_SAVE_EXPO_FREE (expo);
356   return mpfr_check_range (y, res, rnd_mode);
357 }
358 
359 int
mpfr_sub_q(mpfr_ptr y,mpfr_srcptr x,mpq_srcptr z,mpfr_rnd_t rnd_mode)360 mpfr_sub_q (mpfr_ptr y, mpfr_srcptr x, mpq_srcptr z,mpfr_rnd_t rnd_mode)
361 {
362   mpfr_t t,q;
363   mpfr_prec_t p;
364   int res;
365   mpfr_exp_t err;
366   MPFR_SAVE_EXPO_DECL (expo);
367   MPFR_ZIV_DECL (loop);
368 
369   if (MPFR_UNLIKELY (MPFR_IS_SINGULAR (x)))
370     {
371       if (MPFR_IS_NAN (x))
372         {
373           MPFR_SET_NAN (y);
374           MPFR_RET_NAN;
375         }
376       else if (MPFR_IS_INF (x))
377         {
378           if (MPFR_UNLIKELY (mpz_sgn (mpq_denref (z)) == 0 &&
379                              MPFR_MULT_SIGN (mpz_sgn (mpq_numref (z)),
380                                              MPFR_SIGN (x)) >= 0))
381             {
382               MPFR_SET_NAN (y);
383               MPFR_RET_NAN;
384             }
385           MPFR_SET_INF (y);
386           MPFR_SET_SAME_SIGN (y, x);
387           MPFR_RET (0);
388         }
389       else
390         {
391           MPFR_ASSERTD (MPFR_IS_ZERO (x));
392 
393           if (MPFR_UNLIKELY (mpq_sgn (z) == 0))
394             return mpfr_set (y, x, rnd_mode); /* signed 0 - Unsigned 0 */
395           else
396             {
397               res =  mpfr_set_q (y, z, MPFR_INVERT_RND (rnd_mode));
398               MPFR_CHANGE_SIGN (y);
399               return -res;
400             }
401         }
402     }
403 
404   MPFR_SAVE_EXPO_MARK (expo);
405 
406   p = MPFR_PREC (y) + 10;
407   mpfr_init2 (t, p);
408   mpfr_init2 (q, p);
409 
410   MPFR_ZIV_INIT (loop, p);
411   for(;;)
412     {
413       MPFR_BLOCK_DECL (flags);
414 
415       res = mpfr_set_q(q, z, MPFR_RNDN);  /* Error <= 1/2 ulp(q) */
416       /* If z if @INF@ (1/0), res = 0, so it quits immediately */
417       if (MPFR_UNLIKELY (res == 0))
418         /* Result is exact so we can add it directly!*/
419         {
420           res = mpfr_sub (y, x, q, rnd_mode);
421           break;
422         }
423       MPFR_BLOCK (flags, mpfr_sub (t, x, q, MPFR_RNDN));
424       /* Error on t is <= 1/2 ulp(t), except in case of overflow/underflow,
425          but such an exception is very unlikely as it would be possible
426          only if q has a huge numerator or denominator. Not supported! */
427       MPFR_ASSERTN (! (MPFR_OVERFLOW (flags) || MPFR_UNDERFLOW (flags)));
428       /* Error / ulp(t)      <= 1/2 + 1/2 * 2^(EXP(q)-EXP(t))
429          If EXP(q)-EXP(t)>0, <= 2^(EXP(q)-EXP(t)-1)*(1+2^-(EXP(q)-EXP(t)))
430                              <= 2^(EXP(q)-EXP(t))
431                              If EXP(q)-EXP(t)<0, <= 2^0 */
432       /* We can get 0, but we can't round since q is inexact */
433       if (MPFR_LIKELY (!MPFR_IS_ZERO (t)))
434         {
435           err = (mpfr_exp_t) p - 1 - MAX (MPFR_GET_EXP(q)-MPFR_GET_EXP(t), 0);
436           res = MPFR_CAN_ROUND (t, err, MPFR_PREC (y), rnd_mode);
437           if (MPFR_LIKELY (res != 0))  /* We can round! */
438             {
439               res = mpfr_set (y, t, rnd_mode);
440               break;
441             }
442         }
443       MPFR_ZIV_NEXT (loop, p);
444       mpfr_set_prec (t, p);
445       mpfr_set_prec (q, p);
446     }
447   MPFR_ZIV_FREE (loop);
448   mpfr_clear (t);
449   mpfr_clear (q);
450 
451   MPFR_SAVE_EXPO_FREE (expo);
452   return mpfr_check_range (y, res, rnd_mode);
453 }
454 
455 int
mpfr_cmp_q(mpfr_srcptr x,mpq_srcptr q)456 mpfr_cmp_q (mpfr_srcptr x, mpq_srcptr q)
457 {
458   mpfr_t t;
459   int res;
460   mpfr_prec_t p;
461   MPFR_SAVE_EXPO_DECL (expo);
462 
463   /* GMP allows the user to set the denominator to 0. This is interpreted
464      by MPFR as the value being an infinity or NaN (probably better than
465      an assertion failure). */
466   if (MPFR_UNLIKELY (mpz_sgn (mpq_denref (q)) == 0))
467     {
468       /* q is an infinity or NaN */
469       mpfr_flags_t old_flags;
470 
471       mpfr_init2 (t, MPFR_PREC_MIN);
472       old_flags = __gmpfr_flags;
473       mpfr_set_q (t, q, MPFR_RNDN);
474       __gmpfr_flags = old_flags;
475       res = mpfr_cmp (x, t);
476       mpfr_clear (t);
477       return res;
478     }
479 
480   if (MPFR_UNLIKELY (MPFR_IS_SINGULAR (x)))
481     return mpfr_cmp_si (x, mpq_sgn (q));
482 
483   MPFR_SAVE_EXPO_MARK (expo);
484 
485   /* x < a/b ? <=> x*b < a */
486   MPFR_MPZ_SIZEINBASE2 (p, mpq_denref (q));
487   mpfr_init2 (t, MPFR_PREC(x) + p);
488   res = mpfr_mul_z (t, x, mpq_denref (q), MPFR_RNDN);
489   MPFR_ASSERTD (res == 0);
490   res = mpfr_cmp_z (t, mpq_numref (q));
491   mpfr_clear (t);
492 
493   MPFR_SAVE_EXPO_FREE (expo);
494   return res;
495 }
496 #endif
497 
498 #ifndef MPFR_USE_MINI_GMP
499 int
mpfr_cmp_f(mpfr_srcptr x,mpf_srcptr z)500 mpfr_cmp_f (mpfr_srcptr x, mpf_srcptr z)
501 {
502   mpfr_t t;
503   int res;
504   MPFR_SAVE_EXPO_DECL (expo);
505 
506   if (MPFR_UNLIKELY (MPFR_IS_SINGULAR (x)))
507     return mpfr_cmp_si (x, mpf_sgn (z));
508 
509   MPFR_SAVE_EXPO_MARK (expo);
510 
511   mpfr_init2 (t, MPFR_PREC_MIN + ABSIZ(z) * GMP_NUMB_BITS);
512   res = mpfr_set_f (t, z, MPFR_RNDN);
513   MPFR_ASSERTD (res == 0);
514   res = mpfr_cmp (x, t);
515   mpfr_clear (t);
516 
517   MPFR_SAVE_EXPO_FREE (expo);
518   return res;
519 }
520 #endif
521