1 //===-- lib/extendsfdf2.c - single -> double conversion -----------*- C -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is dual licensed under the MIT and the University of Illinois Open
6 // Source Licenses. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implements a fairly generic conversion from a narrower to a wider
11 // IEEE-754 floating-point type. The constants and types defined following the
12 // includes below parameterize the conversion.
14 // This routine can be trivially adapted to support conversions from
15 // half-precision or to quad-precision. It does not support types that don't
16 // use the usual IEEE-754 interchange formats; specifically, some work would be
17 // needed to adapt it to (for example) the Intel 80-bit format or PowerPC
18 // double-double format.
20 // Note please, however, that this implementation is only intended to support
21 // *widening* operations; if you need to convert to a *narrower* floating-point
22 // type (e.g. double -> float), then this routine will not do what you want it
25 // It also requires that integer types at least as large as both formats
26 // are available on the target platform; this may pose a problem when trying
27 // to add support for quad on some 32-bit systems, for example. You also may
28 // run into trouble finding an appropriate CLZ function for wide source types;
29 // you will likely need to roll your own on some platforms.
31 // Finally, the following assumptions are made:
33 // 1. floating-point types and integer types have the same endianness on the
36 // 2. quiet NaNs, if supported, are indicated by the leading bit of the
37 // significand field being set
39 //===----------------------------------------------------------------------===//
44 typedef uint32_t src_rep_t
;
45 #define SRC_REP_C UINT32_C
46 static const int srcSigBits
= 23;
47 #define src_rep_t_clz __builtin_clz
50 typedef uint64_t dst_rep_t
;
51 #define DST_REP_C UINT64_C
52 static const int dstSigBits
= 52;
54 // End of specialization parameters. Two helper routines for conversion to and
55 // from the representation of floating-point data as integer values follow.
57 static inline src_rep_t
srcToRep(src_t x
) {
58 const union { src_t f
; src_rep_t i
; } rep
= {.f
= x
};
62 static inline dst_t
dstFromRep(dst_rep_t x
) {
63 const union { dst_t f
; dst_rep_t i
; } rep
= {.i
= x
};
67 // End helper routines. Conversion implementation follows.
69 ARM_EABI_FNALIAS(f2d
, extendsfdf2
)
71 dst_t
__extendsfdf2(src_t a
) {
73 // Various constants whose values follow from the type parameters.
74 // Any reasonable optimizer will fold and propagate all of these.
75 const int srcBits
= sizeof(src_t
)*CHAR_BIT
;
76 const int srcExpBits
= srcBits
- srcSigBits
- 1;
77 const int srcInfExp
= (1 << srcExpBits
) - 1;
78 const int srcExpBias
= srcInfExp
>> 1;
80 const src_rep_t srcMinNormal
= SRC_REP_C(1) << srcSigBits
;
81 const src_rep_t srcInfinity
= (src_rep_t
)srcInfExp
<< srcSigBits
;
82 const src_rep_t srcSignMask
= SRC_REP_C(1) << (srcSigBits
+ srcExpBits
);
83 const src_rep_t srcAbsMask
= srcSignMask
- 1;
84 const src_rep_t srcQNaN
= SRC_REP_C(1) << (srcSigBits
- 1);
85 const src_rep_t srcNaNCode
= srcQNaN
- 1;
87 const int dstBits
= sizeof(dst_t
)*CHAR_BIT
;
88 const int dstExpBits
= dstBits
- dstSigBits
- 1;
89 const int dstInfExp
= (1 << dstExpBits
) - 1;
90 const int dstExpBias
= dstInfExp
>> 1;
92 const dst_rep_t dstMinNormal
= DST_REP_C(1) << dstSigBits
;
94 // Break a into a sign and representation of the absolute value
95 const src_rep_t aRep
= srcToRep(a
);
96 const src_rep_t aAbs
= aRep
& srcAbsMask
;
97 const src_rep_t sign
= aRep
& srcSignMask
;
100 if (aAbs
- srcMinNormal
< srcInfinity
- srcMinNormal
) {
101 // a is a normal number.
102 // Extend to the destination type by shifting the significand and
103 // exponent into the proper position and rebiasing the exponent.
104 absResult
= (dst_rep_t
)aAbs
<< (dstSigBits
- srcSigBits
);
105 absResult
+= (dst_rep_t
)(dstExpBias
- srcExpBias
) << dstSigBits
;
108 else if (aAbs
>= srcInfinity
) {
109 // a is NaN or infinity.
110 // Conjure the result by beginning with infinity, then setting the qNaN
111 // bit (if needed) and right-aligning the rest of the trailing NaN
113 absResult
= (dst_rep_t
)dstInfExp
<< dstSigBits
;
114 absResult
|= (dst_rep_t
)(aAbs
& srcQNaN
) << (dstSigBits
- srcSigBits
);
115 absResult
|= aAbs
& srcNaNCode
;
120 // renormalize the significand and clear the leading bit, then insert
121 // the correct adjusted exponent in the destination type.
122 const int scale
= src_rep_t_clz(aAbs
) - src_rep_t_clz(srcMinNormal
);
123 absResult
= (dst_rep_t
)aAbs
<< (dstSigBits
- srcSigBits
+ scale
);
124 absResult
^= dstMinNormal
;
125 const int resultExponent
= dstExpBias
- srcExpBias
- scale
+ 1;
126 absResult
|= (dst_rep_t
)resultExponent
<< dstSigBits
;
134 // Apply the signbit to (dst_t)abs(a).
135 const dst_rep_t result
= absResult
| (dst_rep_t
)sign
<< (dstBits
- srcBits
);
136 return dstFromRep(result
);