fp_lib.h revision 9ad441ffec97db647fee3725b3424284fb913e14 
1//===-- lib/fp_lib.h - Floating-point utilities -------------------*- C -*-===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is dual licensed under the MIT and the University of Illinois Open
6// Source Licenses. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// This file is a configuration header for soft-float routines in compiler-rt.
11// This file does not provide any part of the compiler-rt interface, but defines
12// many useful constants and utility routines that are used in the
13// implementation of the soft-float routines in compiler-rt.
14//
15// Assumes that float and double correspond to the IEEE-754 binary32 and
16// binary64 types, respectively, and that integer endianness matches floating
17// point endianness on the target platform.
18//
19//===----------------------------------------------------------------------===//
20
21#ifndef FP_LIB_HEADER
22#define FP_LIB_HEADER
23
24#include <stdint.h>
25#include <stdbool.h>
26#include <limits.h>
27
28#if defined SINGLE_PRECISION
29
30typedef uint32_t rep_t;
31typedef int32_t srep_t;
32typedef float fp_t;
33#define REP_C UINT32_C
34#define significandBits 23
35
36static inline int rep_clz(rep_t a) {
37    return __builtin_clz(a);
38}
39
40// 32x32 --> 64 bit multiply
41static inline void wideMultiply(rep_t a, rep_t b, rep_t *hi, rep_t *lo) {
42    const uint64_t product = (uint64_t)a*b;
43    *hi = product >> 32;
44    *lo = product;
45}
46
47#elif defined DOUBLE_PRECISION
48
49typedef uint64_t rep_t;
50typedef int64_t srep_t;
51typedef double fp_t;
52#define REP_C UINT64_C
53#define significandBits 52
54
55static inline int rep_clz(rep_t a) {
56#if defined __LP64__
57    return __builtin_clzl(a);
58#else
59    if (a & REP_C(0xffffffff00000000))
60        return __builtin_clz(a >> 32);
61    else
62        return 32 + __builtin_clz(a & REP_C(0xffffffff));
63#endif
64}
65
66#define loWord(a) (a & 0xffffffffU)
67#define hiWord(a) (a >> 32)
68
69// 64x64 -> 128 wide multiply for platforms that don't have such an operation;
70// many 64-bit platforms have this operation, but they tend to have hardware
71// floating-point, so we don't bother with a special case for them here.
72static inline void wideMultiply(rep_t a, rep_t b, rep_t *hi, rep_t *lo) {
73    // Each of the component 32x32 -> 64 products
74    const uint64_t plolo = loWord(a) * loWord(b);
75    const uint64_t plohi = loWord(a) * hiWord(b);
76    const uint64_t philo = hiWord(a) * loWord(b);
77    const uint64_t phihi = hiWord(a) * hiWord(b);
78    // Sum terms that contribute to lo in a way that allows us to get the carry
79    const uint64_t r0 = loWord(plolo);
80    const uint64_t r1 = hiWord(plolo) + loWord(plohi) + loWord(philo);
81    *lo = r0 + (r1 << 32);
82    // Sum terms contributing to hi with the carry from lo
83    *hi = hiWord(plohi) + hiWord(philo) + hiWord(r1) + phihi;
84}
85
86#else
87#error Either SINGLE_PRECISION or DOUBLE_PRECISION must be defined.
88#endif
89
90#define typeWidth       (sizeof(rep_t)*CHAR_BIT)
91#define exponentBits    (typeWidth - significandBits - 1)
92#define maxExponent     ((1 << exponentBits) - 1)
93#define exponentBias    (maxExponent >> 1)
94
95#define implicitBit     (REP_C(1) << significandBits)
96#define significandMask (implicitBit - 1U)
97#define signBit         (REP_C(1) << (significandBits + exponentBits))
98#define absMask         (signBit - 1U)
99#define exponentMask    (absMask ^ significandMask)
100#define oneRep          ((rep_t)exponentBias << significandBits)
101#define infRep          exponentMask
102#define quietBit        (implicitBit >> 1)
103#define qnanRep         (exponentMask | quietBit)
104
105static inline rep_t toRep(fp_t x) {
106    const union { fp_t f; rep_t i; } rep = {.f = x};
107    return rep.i;
108}
109
110static inline fp_t fromRep(rep_t x) {
111    const union { fp_t f; rep_t i; } rep = {.i = x};
112    return rep.f;
113}
114
115static inline int normalize(rep_t *significand) {
116    const int shift = rep_clz(*significand) - rep_clz(implicitBit);
117    *significand <<= shift;
118    return 1 - shift;
119}
120
121static inline void wideLeftShift(rep_t *hi, rep_t *lo, int count) {
122    *hi = *hi << count | *lo >> (typeWidth - count);
123    *lo = *lo << count;
124}
125
126static inline void wideRightShiftWithSticky(rep_t *hi, rep_t *lo, int count) {
127    if (count < typeWidth) {
128        const bool sticky = *lo << (typeWidth - count);
129        *lo = *hi << (typeWidth - count) | *lo >> count | sticky;
130        *hi = *hi >> count;
131    }
132    else if (count < 2*typeWidth) {
133        const bool sticky = *hi << (2*typeWidth - count) | *lo;
134        *lo = *hi >> (count - typeWidth) | sticky;
135        *hi = 0;
136    } else {
137        const bool sticky = *hi | *lo;
138        *lo = sticky;
139        *hi = 0;
140    }
141}
142
143#endif // FP_LIB_HEADER
144