1 /* mpfr_get_flt -- convert a mpfr_t to a machine single precision float
3 Copyright 2009-2015 Free Software Foundation, Inc.
4 Contributed by the AriC and Caramel projects, INRIA.
6 This file is part of the GNU MPFR Library.
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.
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.
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 http://www.gnu.org/licenses/ or write to the Free Software Foundation, Inc.,
21 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA. */
23 #include <float.h> /* for FLT_MIN */
25 #define MPFR_NEED_LONGLONG_H
26 #include "mpfr-impl.h"
28 #include "ieee_floats.h"
30 #define FLT_NEG_ZERO ((float) DBL_NEG_ZERO)
31 #define MPFR_FLT_INFM ((float) MPFR_DBL_INFM)
32 #define MPFR_FLT_INFP ((float) MPFR_DBL_INFP)
35 mpfr_get_flt (mpfr_srcptr src
, mpfr_rnd_t rnd_mode
)
41 /* in case of NaN, +Inf, -Inf, +0, -0, the conversion from double to float
43 if (MPFR_UNLIKELY (MPFR_IS_SINGULAR (src
)))
44 return (float) mpfr_get_d (src
, rnd_mode
);
46 e
= MPFR_GET_EXP (src
);
47 negative
= MPFR_IS_NEG (src
);
49 if (MPFR_UNLIKELY(rnd_mode
== MPFR_RNDA
))
50 rnd_mode
= negative
? MPFR_RNDD
: MPFR_RNDU
;
52 /* the smallest positive normal float number is 2^(-126) = 0.5*2^(-125),
53 and the smallest positive subnormal number is 2^(-149) = 0.5*2^(-148) */
54 if (MPFR_UNLIKELY (e
< -148))
56 /* |src| < 2^(-149), i.e., |src| is smaller than the smallest positive
58 In round-to-nearest mode, 2^(-150) is rounded to zero.
61 (rnd_mode
== MPFR_RNDD
||
62 (rnd_mode
== MPFR_RNDN
&& mpfr_cmp_si_2exp (src
, -1, -150) < 0)
63 ? -FLT_MIN
: FLT_NEG_ZERO
) :
64 (rnd_mode
== MPFR_RNDU
||
65 (rnd_mode
== MPFR_RNDN
&& mpfr_cmp_si_2exp (src
, 1, -150) > 0)
67 if (d
!= 0.0) /* we multiply FLT_MIN = 2^(-126) by FLT_EPSILON = 2^(-23)
71 /* the largest normal number is 2^128*(1-2^(-24)) = 0.111...111e128 */
72 else if (MPFR_UNLIKELY (e
> 128))
75 (rnd_mode
== MPFR_RNDZ
|| rnd_mode
== MPFR_RNDU
?
76 -FLT_MAX
: MPFR_FLT_INFM
) :
77 (rnd_mode
== MPFR_RNDZ
|| rnd_mode
== MPFR_RNDD
?
78 FLT_MAX
: MPFR_FLT_INFP
);
80 else /* -148 <= e <= 127 */
84 mp_limb_t tp
[MPFR_LIMBS_PER_FLT
];
88 nbits
= IEEE_FLT_MANT_DIG
; /* 24 */
89 if (MPFR_UNLIKELY (e
< -125))
90 /*In the subnormal case, compute the exact number of significant bits*/
93 MPFR_ASSERTD (nbits
>= 1);
95 np
= MPFR_PREC2LIMBS (nbits
);
96 MPFR_ASSERTD(np
<= MPFR_LIMBS_PER_FLT
);
97 carry
= mpfr_round_raw_4 (tp
, MPFR_MANT(src
), MPFR_PREC(src
), negative
,
99 /* we perform the reconstruction using the 'double' type here,
100 knowing the result is exactly representable as 'float' */
101 if (MPFR_UNLIKELY(carry
))
105 /* The following computations are exact thanks to the previous
107 dd
= (double) tp
[0] / MP_BASE_AS_DOUBLE
;
108 for (i
= 1 ; i
< np
; i
++)
109 dd
= (dd
+ tp
[i
]) / MP_BASE_AS_DOUBLE
;
110 /* dd is the mantissa (between 1/2 and 1) of the argument rounded
113 dd
= mpfr_scale2 (dd
, e
);
117 /* convert (exacly) to float */